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diff --git a/31627-h/31627-h.htm b/31627-h/31627-h.htm new file mode 100644 index 0000000..a8b2e7e --- /dev/null +++ b/31627-h/31627-h.htm @@ -0,0 +1,10702 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" /> +<title>The Project Gutenberg eBook of Volcanoes: Past and Present, by Edward Hull</title> + <style type="text/css"> + +body { + margin-left: 10%; + margin-right: 10%; +} + + h1,h2,h3,h4,h5,h6 { + text-align: center; /* all headings centered */ + clear: both; +} + +p { + margin-top: .75em; + text-align: justify; + margin-bottom: .75em; +} + +hr { + width: 33%; + margin-top: 2em; + margin-bottom: 2em; + margin-left: auto; + margin-right: auto; + clear: both; +} + +hr.major { + width: 65%; +} + +hr.tb { + width: 45%; +} + +table { + margin-left: auto; + margin-right: auto; +} + +.pagenum { /* uncomment the next line for invisible page numbers */ + /* visibility: hidden; */ + position: absolute; + left: 92%; + font-size: smaller; + text-align: right; +} /* page numbers */ + +.linenum { + position: absolute; + top: auto; + left: 4%; +} /* poetry number */ + +.blockquot { + margin-left: 5%; + margin-right: 10%; +} + +.sidenote { + width: 20%; + padding-bottom: .5em; + padding-top: .5em; + padding-left: .5em; + padding-right: .5em; + margin-left: 1em; + float: right; + clear: right; + margin-top: 1em; + font-size: smaller; + color: black; + background: #eeeeee; + border: dashed 1px; +} + +.bb {border-bottom: solid 2px;} + +.bl {border-left: solid 2px;} + +.bt {border-top: solid 2px;} + +.br {border-right: solid 2px;} + +.bbox {border: solid 2px;} + +.center {text-align: center;} + +.smcap {font-variant: small-caps;} + +.u {text-decoration: underline;} + +.caption {font-weight: bold;} + +/* Images */ +.figcenter { + margin: auto; + text-align: center; +} + +.figcaption { + margin-left:10%; + margin-right:10%; +} + +.figleft { + float: left; + clear: left; + margin-left: 0; + margin-bottom: 1em; + margin-top: 1em; + margin-right: 1em; + padding: 0; + text-align: center; +} + +.figright { + float: right; + clear: right; + margin-left: 1em; + margin-bottom: + 1em; + margin-top: 1em; + margin-right: 0; + padding: 0; + text-align: center; +} + +/* Footnotes */ +.footnotes {border: dashed 1px;} + +.footnote {margin-left: 10%; margin-right: 10%; font-size: 0.9em;} + +.footnote .label {position: absolute; right: 84%; text-align: right;} + +.fnanchor { + vertical-align: super; + font-size: .8em; + text-decoration: + none; +} + +/* Poetry */ +.poem { + margin-left:10%; + margin-right:10%; + text-align: left; +} + +.poem br {display: none;} + +.poem .stanza {margin: 1em 0em 1em 0em;} + +.poem span.i0 { + display: block; + margin-left: 0em; + padding-left: 3em; + text-indent: -3em; +} + +.poem span.i2 { + display: block; + margin-left: 2em; + padding-left: 3em; + text-indent: -3em; +} + +.poem span.i4 { + display: block; + margin-left: 4em; + padding-left: 3em; + text-indent: -3em; +} + +.closing { + margin-left: 60%; +} + +.greek { + border-bottom: 1px dashed gray; +} + + hr.full { width: 100%; + margin-top: 3em; + margin-bottom: 0em; + margin-left: auto; + margin-right: auto; + height: 4px; + border-width: 4px 0 0 0; /* remove all borders except the top one */ + border-style: solid; + border-color: #000000; + clear: both; } + pre {font-size: 85%;} + </style> +</head> +<body> +<h1>The Project Gutenberg eBook, Volcanoes: Past and Present, by Edward Hull</h1> +<pre> +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at <a href = "http://www.gutenberg.org">www.gutenberg.org</a></pre> +<p>Title: Volcanoes: Past and Present</p> +<p>Author: Edward Hull</p> +<p>Release Date: March 13, 2010 [eBook #31627]</p> +<p>Language: English</p> +<p>Character set encoding: ISO-8859-1</p> +<p>***START OF THE PROJECT GUTENBERG EBOOK VOLCANOES: PAST AND PRESENT***</p> +<p> </p> +<h3>E-text prepared by Steven Gibbs, Stephen H. Sentoff,<br /> + and the Project Gutenberg Online Distributed Proofreading Team<br /> + (http://www.pgdp.net)</h3> +<p> </p> +<hr class="full" /> +<p> </p> +<p> </p> +<p> </p> + +<p class="center"><span class="pagenum"><a name="Page_i" id="Page_i">[Pg i]</a></span> +<i>THE CONTEMPORARY SCIENCE SERIES.</i></p> + +<p class="center"><span class="smcap">Edited by</span> HAVELOCK ELLIS.</p> + +<hr /> + + +<h1>VOLCANOES:<br /> + +PAST AND PRESENT.</h1> + +<p><span class="pagenum"><a name="Page_ii" id="Page_ii">[Pg ii]</a></span></p> +<hr class="major" /> +<div class="figcenter"> +<a name="FIGURE_1"> + <img src="images/figure1.jpg" alt="Eruption of Vesuvius" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 1.</span>—Eruption of Vesuvius, 1872-1873 +<br /><i>(From a Photograph by Negretti and Zambra).</i> +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></p> +<hr class="major" /> +<h1>VOLCANOES:<br /> +PAST AND PRESENT. +</h1> +<hr /> +<h3>BY</h3> +<h2>EDWARD HULL, M.A., LL.D., F.R.S.</h2> +<p class="center"><i>Examiner in Geology to the University of London.</i></p> +<hr /> + +<p class="center">WITH 41 ILLUSTRATIONS AND 4 PLATES +OF ROCK-SECTIONS.</p> +<hr /> + +<p class="center">LONDON:<br/> +WALTER SCOTT, <span class="smcap">Limited</span>,<br /> +24, WARWICK LANE, PATERNOSTER ROW.</p> + +<p class="center">1892. +</p> + + + +<p><span class="pagenum"><a name="Page_v" id="Page_v">[Pg v]</a></span></p> +<hr class="major" /> +<p><i>By THE SAME AUTHOR.</i></p> + +<blockquote><p><b>The Coal-fields of Great Britain: their +History, Structure, and Resources.</b> 4th edit. (1881.) E. +Stanford.</p> + +<p><b>The Physical History of the British Isles.</b> +With a Dissertation on the Origin of Western Europe and of +the Atlantic Ocean. (1882.) E. Stanford.</p> + +<p><b>The Physical Geology and Geography of +Ireland.</b> 2nd edit. (1891.) E. Stanford.</p> + +<p><b>Treatise on the Building and Ornamental +Stones of Great Britain and Foreign Countries.</b> (1872.) +Macmillan and Co.</p> + +<p><b>Memoir on the Physical Geology and +Geography of Arabia-Petræa, Palestine, and adjoining Districts.</b> +(1886.) Committee of the Palestine Exploration Fund.</p> + +<p><b>Mount Seir, Sinai, and Western Palestine.</b> +Being a Narrative of a Scientific Expedition, 1883-84. (1885.) +Committee of the Palestine Exploration Fund.</p> + +<p><b>Text-book of Physiography.</b> (1888.) C. W. +Deacon and Co.</p> + +<p><b>Sketch of Geological History.</b> (1887.) C. W. +Deacon and Co.</p></blockquote> + +<p><span class="pagenum"><a name="Page_vii" id="Page_vii">[Pg vii]</a></span></p> + +<hr class="major" /> +<h2><a name="PREFACE" id="PREFACE"></a>PREFACE.</h2> + + +<p>It has not been my object to present in the following +pages even an approximately complete description +of the volcanic and seismic phenomena of the globe; +such an undertaking would involve an amount of +labour which few would be bold enough to attempt; +nor would it be compatible with the aims of the +<i>Contemporary Science Series</i>.</p> + +<p>I have rather chosen to illustrate the most recent +conclusions regarding the phenomena and origin of +volcanic action, by the selection of examples drawn +from the districts where these phenomena have been +most carefully observed and recorded under the light +of modern geological science. I have also endeavoured +to show, by illustrations carried back into later geological +epochs, how the volcanic phenomena of the +present day do not differ in kind, though they may +in degree, from those of the past history of our globe. +For not only do the modes of eruption of volcanic +materials in past geological times resemble those of +the present or human epoch, but the materials themselves +<span class="pagenum"><a name="Page_viii" id="Page_viii">[Pg viii]</a></span>are so similar in character that it is only in +consequence of alterations in structure or composition +which the original materials have undergone, since +their extrusion, that any important distinctions can +be recognised between the volcanic products of recent +times and those of earlier periods.</p> + +<p>I have, finally, endeavoured to find an answer to +two interesting and important questions: (1) Are we +now living in an epoch of extraordinary volcanic +energy?—a question which such terrible outbursts +as we have recently witnessed in Japan, the Malay +Archipelago, and even in Italy, naturally suggest; +and (2) What is the ultimate cause of volcanic +action? On this latter point I am gratified to find +that my conclusions are in accordance with those +expounded by one who has been appropriately +designated "the Nestor of Modern Geology," Professor +Prestwich.</p> + +<p>Within the last few years the study of the structure +and composition of volcanic rocks, by means of the +microscope brought to bear on their translucent +sections, has added wonderfully to our knowledge +of such rocks, and has become a special branch of +petrological investigation. Commenced by Sorby, +and carried on by Allport, Zirkel, Rosenbusch, Von +Lasaulx, Teall, and many more enthusiastic students, +it has thrown a flood of light upon our knowledge of +the mutual relations of the component minerals of +igneous masses, the alteration these minerals have +undergone in some cases, and the conditions under +<span class="pagenum"><a name="Page_ix" id="Page_ix">[Pg ix]</a></span>which they have been erupted and consolidated. But +nothing that has been observed has tended materially +to alter conclusions arrived at by other processes of +reasoning regarding volcanic phenomena, and for +these we have to fall back upon observations conducted +in the field on a more or less large scale, +and carried on before, during, and after eruptions. +Macroscopic and microscopic observations have to +go hand in hand in the study of volcanic phenomena.</p> + +<p class="closing"> +E. H. +</p> + +<p><span class="pagenum"><a name="Page_xi" id="Page_xi">[Pg xi]</a></span></p> + +<hr class="major" /> +<h2><a name="CONTENTS" id="CONTENTS"></a>CONTENTS.</h2> + + + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="center" colspan="3"><b>PART I.</b></td></tr> +<tr><td align="center" colspan="3"><i>INTRODUCTION.</i></td></tr> +<tr><td align="right"></td><td align="left"></td><td align="right">PAGE</td></tr> +<tr><td align="right"><span class="smcap">Chap. I.</span></td> + <td align="left"><a href="#PART_I_CHAPTER_I"><span class="smcap">Historic Notices of Volcanic Action</span></a></td><td align="right">1-9</td></tr> +<tr><td align="right"> " II.</td> + <td align="left"><a href="#PART_I_CHAPTER_II"><span class="smcap">Form, Structure, and Composition of Volcanic Mountains</span></a></td><td align="right">10-19</td></tr> +<tr><td align="right"> " III.</td> + <td align="left"><a href="#PART_I_CHAPTER_III"><span class="smcap">Lines and Groups of Active Volcanic Vents</span></a></td><td align="right">20-29</td></tr> +<tr><td align="right"> " IV.</td> + <td align="left"><a href="#PART_I_CHAPTER_IV"><span class="smcap">Mid-ocean Volcanic Islands</span></a></td><td align="right">30-40</td></tr> +<tr><td align="center" colspan="3"><b>PART II.</b></td></tr> +<tr><td align="center" colspan="3"><i>EUROPEAN VOLCANOES.</i></td></tr> +<tr><td align="right"><span class="smcap">Chap. I.</span></td> + <td align="left"><a href="#PART_II_CHAPTER_I"><span class="smcap">Vesuvius</span></a></td><td align="right">41-60</td></tr> +<tr><td align="right">" II.</td> + <td align="left"><a href="#PART_II_CHAPTER_II"><span class="smcap">Etna</span></a></td><td align="right">61-68</td></tr> +<tr><td align="right">" III.</td> + <td align="left"><a href="#PART_II_CHAPTER_III"><span class="smcap">The Lipari Islands, Stromboli</span></a></td><td align="right">69-75</td></tr> +<tr><td align="right">" IV.</td> + <td align="left"><a href="#PART_II_CHAPTER_IV"><span class="smcap">The Santorin Group</span></a></td><td align="right">76-83</td></tr> +<tr><td align="right">" V.</td> + <td align="left"><a href="#PART_II_CHAPTER_V"><span class="smcap">European Extinct or Dormant Volcanoes</span></a></td><td align="right">84-91</td></tr> +<tr><td align="right">" VI.</td> + <td align="left"><a href="#PART_II_CHAPTER_VI"><span class="smcap">Extinct Volcanoes of Central France</span></a></td><td align="right">92-112</td></tr> +<tr><td align="right">" VII.</td> + <td align="left"><a href="#PART_II_CHAPTER_VII"><span class="smcap">The Volcanic District of the Rhine Valley</span></a></td><td align="right">13-125</td></tr> +<tr><td align="center" colspan="3"><b>PART III.</b></td></tr> +<tr><td align="center" colspan="3"><i>DORMANT OR MORIBUND VOLCANOES OF OTHER PARTS OF THE WORLD.</i></td></tr> +<tr><td align="right"><span class="smcap">Chap. I.</span></td> + <td align="left"><a href="#PART_III_CHAPTER_I"><span class="smcap">Dormant Volcanoes of Palestine and Arabia</span></a></td><td align="right">126-135</td></tr> +<tr><td align="right">" II.</td> + <td align="left"><a href="#PART_III_CHAPTER_II"><span class="smcap">The Volcanic Regions of North America</span></a></td><td align="left">136-145</td></tr> +<tr><td align="right">" III.</td> + <td align="left"><a href="#PART_III_CHAPTER_III"><span class="smcap">Volcanoes of New Zealand</span></a></td><td align="right">146-153</td></tr> +<tr><td align="center" colspan="3"><span class="pagenum"><a name="Page_xii" id="Page_xii">[Pg xii]</a></span><b>PART IV.</b></td></tr> +<tr><td align="center" colspan="3"><i>TERTIARY VOLCANIC DISTRICTS OF THE BRITISH ISLES.</i></td></tr> +<tr><td align="right"><span class="smcap">Chap. I.</span></td> + <td align="left"><a href="#PART_IV_CHAPTER_I"><span class="smcap">Antrim</span></a></td><td align="right">154-159</td></tr> +<tr><td align="right">" II.</td> + <td align="left"><a href="#PART_IV_CHAPTER_II"><span class="smcap">Succession of Volcanic Eruptions</span></a></td><td align="right">160-171</td></tr> +<tr><td align="right">" III.</td> + <td align="left"><a href="#PART_IV_CHAPTER_III"><span class="smcap">Island of Mull and Adjoining Coast</span></a></td><td align="right">172-176</td></tr> +<tr><td align="right">" IV.</td> + <td align="left"><a href="#PART_IV_CHAPTER_IV"><span class="smcap">Isle of Skye</span></a></td><td align="right">177-179</td></tr> +<tr><td align="right">" V.</td> + <td align="left"><a href="#PART_IV_CHAPTER_V"><span class="smcap">The Scuir of Eigg</span></a></td><td align="right">180-184</td></tr> +<tr><td align="right">" VI.</td> + <td align="left"><a href="#PART_IV_CHAPTER_VI"><span class="smcap">Isle of Staffa</span></a></td><td align="right">185-186</td></tr> +<tr><td align="center" colspan="3"><b>PART V.</b></td></tr> +<tr><td align="center" colspan="3"><i>PRE-TERTIARY VOLCANIC ROCKS.</i></td></tr> +<tr><td align="right"><span class="smcap">Chap. I.</span></td> + <td align="left"><a href="#PART_V_CHAPTER_I"><span class="smcap">The Deccan Trap-series of India</span></a></td><td align="left">187-189</td></tr> +<tr><td align="right">" II.</td> + <td align="left"><a href="#PART_V_CHAPTER_II"><span class="smcap">Abyssinian Table-lands</span></a></td><td align="right">190-193</td></tr> +<tr><td align="right">" III.</td> + <td align="left"><a href="#PART_V_CHAPTER_III"><span class="smcap">Cape Colony</span></a></td><td align="right">194-195</td></tr> +<tr><td align="right">" IV.</td> + <td align="left"><a href="#PART_V_CHAPTER_IV"><span class="smcap">Volcanic Rocks of Past Geological Periods of the British Isles</span></a></td><td align="left">196-199</td></tr> +<tr><td align="center" colspan="3"><b>PART VI.</b></td></tr> +<tr><td align="center" colspan="3"><i>SPECIAL VOLCANIC AND SEISMIC PHENOMENA.</i></td></tr> +<tr><td align="right"><span class="smcap">Chap. I.</span></td> + <td align="left"><a href="#PART_VI_CHAPTER_I"><span class="smcap">The Eruption of Krakatoa in 1883</span></a></td><td align="right">201-216</td></tr> +<tr><td align="right">" II.</td> + <td align="left"><a href="#PART_VI_CHAPTER_II"><span class="smcap">Earthquakes</span></a></td><td align="right">217-224</td></tr> +<tr><td align="center" colspan="3"><b>PART VII.</b></td></tr> +<tr><td align="center" colspan="3"><i>VOLCANIC AND SEISMIC PROBLEMS.</i></td></tr> +<tr><td align="right"><span class="smcap">Chap. I.</span></td> + <td align="left"><a href="#PART_VII_CHAPTER_I"><span class="smcap">The Ultimate Cause of Volcanic Action</span></a></td><td align="right">225-235</td></tr> +<tr><td align="right">" II.</td> + <td align="left"><a href="#PART_VII_CHAPTER_II"><span class="smcap">Lunar Volcanoes</span></a></td><td align="right">236-252</td></tr> +<tr><td align="right">" III.</td> + <td align="left"><a href="#PART_VII_CHAPTER_III"><span class="smcap">Are we Living in an Epoch of Special Volcanic Activity?</span></a></td><td align="right">253-257</td></tr> +<tr><td align="center" colspan="3"><b>APPENDIX.</b></td></tr> +<tr><td align="left" colspan="2"><a href="#APPENDIX"><span class="smcap">A Brief Account of the Principal Varieties of Volcanic Rocks</span></a></td><td align="right">259-265</td></tr> +<tr><td align="left" colspan="2"><a href="#INDEX"><span class="smcap">Index</span></a></td><td align="right">268</td></tr> +</table></div> + +<p><span class="pagenum"><a name="Page_xiii" id="Page_xiii">[Pg xiii]</a></span></p> + + +<hr class="major" /> +<h2><a name="ILLUSTRATIONS" id="ILLUSTRATIONS"></a>ILLUSTRATIONS.</h2> + + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr><td align="right"><span class="smcap">Fig. 1.</span></td> + <td align="left"><a href="#FIGURE_1"> + <span class="smcap">Eruption of Vesuvius, 1872-73</span></a></td> + <td align="right"><i>Frontispiece</i></td></tr> +<tr><td align="right">" 2.</td> + <td align="left"><a href="#FIGURE_2"> + <span class="smcap">Cotopaxi</span></a></td> + <td align="right"><i>Page</i> 16</td></tr> +<tr><td align="right">" 3.</td> + <td align="left"><a href="#FIGURE_3"> + <span class="smcap">Volcanic Cone of Orizaba</span></a></td> + <td align="right">" 21</td></tr> +<tr><td align="right"></td> + <td align="left"><a href="#MAP_1"> + <span class="smcap">Map of the World, showing Active and Extinct Volcanoes</span></a></td> + <td align="right">" 23</td></tr> +<tr><td align="right">" 4.</td> + <td align="left"><a href="#FIGURE_4"> + <span class="smcap">Teneriffe, seen from the Ocean</span></a></td> + <td align="right">" 31</td></tr> +<tr><td align="right">" 5.</td> + <td align="left"><a href="#FIGURE_5"> + <span class="smcap">View of the Summit of Teneriffe</span></a></td> + <td align="right">" 35</td></tr> +<tr><td align="right">" 6.</td> + <td align="left"><a href="#FIGURE_6"> + <span class="smcap">Probable Aspect of Vesuvius at Beginning of Christian Era</span></a></td> + <td align="right">" 43</td></tr> +<tr><td align="right">" 7.</td> + <td align="left"><a href="#FIGURE_7"> + <span class="smcap">View of Vesuvius before 1767</span></a></td> + <td align="right">" 50</td></tr> +<tr><td align="right">" 8.</td> + <td align="left"><a href="#FIGURE_8"> + <span class="smcap">Map of District bordering Bay of Naples</span></a></td> + <td align="right">" 52</td></tr> +<tr><td align="right">" 9.</td> + <td align="left"><a href="#FIGURE_9"> + <span class="smcap">View of Vesuvius in 1872</span></a></td> + <td align="right">" 53</td></tr> +<tr><td align="right">" 10.</td> + <td align="left"><a href="#FIGURE_10"> + <span class="smcap">Ideal Section through Etna</span></a></td> + <td align="right">" 63</td></tr> +<tr><td align="right">" 11.</td> + <td align="left"><a href="#FIGURE_11"> + <span class="smcap">Map of the Lipari Islands</span></a></td> + <td align="right">" 70</td></tr> +<tr><td align="right">" 12.</td> + <td align="left"><a href="#FIGURE_12"> + <span class="smcap">The Island of Vulcano in Eruption</span></a></td> + <td align="right">" 71</td></tr> +<tr><td align="right">" 13.</td> + <td align="left"><a href="#FIGURE_13"> + <span class="smcap">Ideal Section through Gulf of Santorin</span></a></td> + <td align="right">" 76</td></tr> +<tr><td align="right">" 14.</td> + <td align="left"><a href="#FIGURE_14"> + <span class="smcap">Bird's-eye View of Gulf of Santorin</span></a></td> + <td align="right">" 79</td></tr> +<tr><td align="right">" 15.</td> + <td align="left"><a href="#FIGURE_15"> + <span class="smcap">Ground Plan of Rocca Monfina</span></a></td> + <td align="right">" 80</td></tr> +<tr><td align="right">" 16.</td> + <td align="left"><a href="#FIGURE_16"> + <span class="smcap">Geological Section of Tiber Valley at Rome</span></a></td> + <td align="right">" 88</td></tr> +<tr><td align="right">" 17.</td> + <td align="left"><a href="#FIGURE_17"> + <span class="smcap">Generalised Section Through the Vale of Clermont</span></a></td> + <td align="right">" 93</td></tr> +<tr><td align="right"><span class="pagenum"><a name="Page_xiv" id="Page_xiv">[Pg xiv]</a></span><span class="smcap">Fig. 18.</span></td> + <td align="left"><a href="#FIGURE_18"> + <span class="smcap">View of Puy de Dôme and Neighbouring Volcanoes</span></a></td> + <td align="right"><i>Page</i> 95</td></tr> +<tr><td align="right">" 19.</td> + <td align="left"><a href="#FIGURE_19"> + <span class="smcap">Mont Demise, seen from the S.E.</span></a></td> + <td align="right">" 103</td></tr> +<tr><td align="right">" 20.</td> + <td align="left"><a href="#FIGURE_20"> + <span class="smcap">Sketch Map of Rhenish Area in the Miocene Epoch</span></a></td> + <td align="right">" 114</td></tr> +<tr><td align="right">" 21.</td> + <td align="left"><a href="#FIGURE_21"> + <span class="smcap">The Volcanic Range of the Siebengebirge</span></a></td> + <td align="right">" 117</td></tr> +<tr><td align="right">" 22.</td> + <td align="left"><a href="#FIGURE_22"> + <span class="smcap">Section of Extinct Crater of the Roderberg</span></a></td> + <td align="right">" 120</td></tr> +<tr><td align="right">" 23.</td> + <td align="left"><a href="#FIGURE_23"> + <span class="smcap">Plan and Section of the Laacher See</span></a></td> + <td align="right">" 122</td></tr> +<tr><td align="right">" 24.</td> + <td align="left"><a href="#FIGURE_24"> + <span class="smcap">Extinct Craters in the Jaulân</span></a></td> + <td align="right">" 130</td></tr> +<tr><td align="right">" 25.</td> + <td align="left"><a href="#FIGURE_25"> + <span class="smcap">Mount Shasta</span></a></td> + <td align="right">" 139</td></tr> +<tr><td align="right">" 26.</td> + <td align="left"><a href="#FIGURE_26"> + <span class="smcap">Forms of Volcanic Tuff-Cones, Auckland</span></a></td> + <td align="right">" 148</td></tr> +<tr><td align="right">" 27.</td> + <td align="left"><a href="#FIGURE_27"> + <span class="smcap">"The White Rocks," Portrush, Co. Antrim</span></a></td> + <td align="right">" 157</td></tr> +<tr><td align="right">" 28.</td> + <td align="left"><a href="#FIGURE_28"> + <span class="smcap">Section across the Volcanic Plateau of Antrim</span></a></td> + <td align="right">" 159</td></tr> +<tr><td align="right">" 29.</td> + <td align="left"><a href="#FIGURE_29"> + <span class="smcap">Section at Templepatrick</span></a></td> + <td align="right">" 161</td></tr> +<tr><td align="right">" 30.</td> + <td align="left"><a href="#FIGURE_30"> + <span class="smcap">Cliff above the Giant's Causeway</span></a></td> + <td align="right">" 163</td></tr> +<tr><td align="right">" 31.</td> + <td align="left"><a href="#FIGURE_31"> + <span class="smcap">The Giant's Causeway, Co. Antrim</span></a></td> + <td align="right">" 165</td></tr> +<tr><td align="right">" 32.</td> + <td align="left"><a href="#FIGURE_32"> + <span class="smcap">"The Chimneys," North Coast of Antrim</span></a></td> + <td align="right">" 166</td></tr> +<tr><td align="right">" 33.</td> + <td align="left"><a href="#FIGURE_33"> + <span class="smcap">Section at Alt na Searmoin, Mull</span></a></td> + <td align="right">" 175</td></tr> +<tr><td align="right">" 34.</td> + <td align="left"><a href="#FIGURE_34"> + <span class="smcap">View of the Scuir of Eigg from the East</span></a></td> + <td align="right">" 181</td></tr> +<tr><td align="right"></td> + <td align="left"><a href="#MAP_2"> + <span class="smcap">Map of Volcanic Band of the Moluccas</span></a></td> + <td align="right">" 200</td></tr> +<tr><td align="right">" 35.</td> + <td align="left"><a href="#FIGURE_35"> + <span class="smcap">Map of the Krakatoa Group of Islands</span></a></td> + <td align="right">" 203</td></tr> +<tr><td align="right">" 36.</td> + <td align="left"><a href="#FIGURE_36"> + <span class="smcap">Section from Verlaten Island through Krakatoa</span></a></td> + <td align="right">" 204</td></tr> +<tr><td align="right"><span class="pagenum"><a name="Page_xv" id="Page_xv">[Pg xv]</a></span><span class="smcap">Fig. 37.</span></td> + <td align="left"><a href="#FIGURE_37"> + <span class="smcap">Isoseismals of the Charleston Earthquake</span></a></td> + <td align="right"><i>Page</i> 223</td></tr> +<tr><td align="right">" 38.</td> + <td align="left"><a href="#FIGURE_38"> + <span class="smcap">Photograph of the Moon's Surface</span></a></td> + <td align="right">" 241</td></tr> +<tr><td align="right">" 39.</td> + <td align="left"><a href="#FIGURE_39"> + <span class="smcap">Portion of the Moon's Surface</span></a></td> + <td align="right">" 243</td></tr> +<tr><td align="right"><i>PLATES.</i></td></tr> +<tr><td align="right">I. & II.</td> + <td align="left"><a href="#PLATE_1"> + <span class="smcap">Magnified Sections of Vesuvian Lavas.</span></a></td> + </tr> +<tr><td align="right">III. & IV.</td> + <td align="left"><a href="#PLATE_3"> + <span class="smcap">Magnified Sections of Volcanic Rocks.</span></a></td> + </tr> +</table></div> + +<p><span class="pagenum"><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + +<hr class="major" /> +<h1>Volcanoes: Past and Present.</h1> + + + +<hr class="major" /> +<h1><a name="PART_I" id="PART_I"></a>PART I. +<br /><br /> +INTRODUCTION.</h1> + + + +<hr class="major" /> +<h2><a name="PART_I_CHAPTER_I" id="PART_I_CHAPTER_I"></a>CHAPTER I. +<br /><br /> +HISTORIC NOTICES OF VOLCANIC ACTION.</h2> + + +<p>There are no manifestations of the forces of Nature +more calculated to inspire us with feelings of awe +and admiration than volcanic eruptions preceded or +accompanied, as they generally are, by earthquake +shocks. Few agents have been so destructive in +their effects; and to the real dangers which follow +such terrestrial convulsions are to be added the +feelings of uncertainty and revulsion which arise from +the fact that the earth upon which we tread, and +which we have been accustomed to regard as the +emblem of stability, may become at any moment the +agent of our destruction. It is, therefore, not surprising +that the ancient Greeks, who, as well as the +Romans, were close observers of the phenomena of +Nature, should have investigated the causes of terrestrial +disturbances, and should have come to some +<span class="pagenum"><a name="Page_2" id="Page_2">[Pg 2]</a></span>conclusions upon them in accordance with the light +they possessed. These terrible forces presented to +the Greeks, who clothed all the operations of Nature +in poetic imagery and deified her forces, their poetical +and mystical side; and as there was a deity for every +natural force, so there was one for earthquakes and +volcanoes. Vulcan, the deformed son of Juno (whose +name bears so strange a resemblance to that of "the +first artificer in iron" of the Bible, Tubal Cain), is +condemned to pass his days under Mount Etna, +fabricating the thunderbolts of Jove, and arms for +the gods and great heroes of antiquity.</p> + +<p>The Pythagoreans appear to have held the doctrine +of a central fire +(<span title="Greek: meson pyr" class="greek">μέσον πῦρ</span>) +as the source of volcanic +phenomena; and in the Dialogues of Plato allusion +is made to a subterranean reservoir of lava, which, +according to Simplicius, was in accordance with +the doctrine of the Pythagoreans which Plato was +recounting.<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a> Thucydides clearly describes the effect +of earthquakes upon coast-lines of the Grecian Archipelago, +similar to that which took place in the case of +the earthquake of Lisbon, the sea first retiring and +afterwards inundating the shore. Pliny supposed +that it was by earthquake avulsion that islands were +naturally formed. Thus Sicily was torn from Italy, +Cyprus from Syria, Eubœa from Bœotia, and the rest; +but this view was previously enunciated by Aristotle +in his +"<span title="Greek: Peri kosmou" class="greek">Περι κοσμου</span>," +where he states that earthquakes +have torn to pieces many parts of the earth, while +lands have been converted into sea, and that tracts +once covered by the sea have been converted into +dry land.</p> + +<p><span class="pagenum"><a name="Page_3" id="Page_3">[Pg 3]</a></span></p><p>But the most philosophical views regarding terrestrial +phenomena are those given by Ovid as having +been held by Pythagoras (about <span class="smcap">B.C.</span> 580). In the +<i>Metamorphoses</i> his views regarding the interchange +of land and sea, the effects of running water in +eroding valleys, the growth of deltas, the effect of +earthquakes in burying cities and diverting streams +from their sources, are remarkable anticipations of +doctrines now generally held.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> But what most concerns +us at present are his views regarding the +changes which have come over volcanic mountains. In +his day Vesuvius was dormant, but Etna was active; +so his illustrations are drawn from the latter mountain; +and in this connection he observes that volcanic vents +shift their position. There was a time, he says, when +Etna was not a burning mountain, and the time will +come when it will cease to burn; whether it be that +some caverns become closed up by the movements +of the earth, or others opened, or whether the fuel +is finally exhausted.<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a> Strabo may be regarded as +<span class="pagenum"><a name="Page_4" id="Page_4">[Pg 4]</a></span>having originated the view, now generally held, that +active volcanoes are safety-valves to the regions in +which they are situated. Referring to the tradition +recorded by Pliny, that Sicily was torn from Italy by +an earthquake, he observes that the land near the sea +in those parts was rarely shaken by earthquakes, since +there are now orifices whereby fire and ignited matters +and waters escape; but formerly, when the volcanoes +of Etna, the Lipari Islands, Ischia, and others were +closed up, the imprisoned fire and wind might have +produced far more violent movements.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a></p> + +<p>The account of the first recorded eruption of +Vesuvius has been graphically related by the younger +Pliny in his two letters to Tacitus, to which I shall +have occasion to refer further on.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> These bring down +the references to volcanic phenomena amongst ancient +authors to the commencement of the Christian era; +from all of which we may infer that the more +enlightened philosophers of antiquity had a general +idea that eruptions had their origin in a central fire +within the interior of the earth, that volcanic mountains +were liable to become dormant for long periods, +and afterwards to break out into renewed activity, +that there existed a connection between volcanic +action and earthquakes, and that volcanoes are safety-valves +for the regions around.</p> + +<p>It is unnecessary that I should pursue the historical +sketch further. Those who wish to know the views +of writers of the Middle Ages will find them recorded +<span class="pagenum"><a name="Page_5" id="Page_5">[Pg 5]</a></span>by Sir Charles Lyell.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> The long controversy carried +on during the latter part of the eighteenth century +between "Neptunists," led by Werner on the one +side, and "Vulcanists," led by Hutton and Playfair +on the other, regarding the origin of such rocks as +granite and basalt, was finally brought to a close by the +triumph of the "Vulcanists," who demonstrated that +such rocks are the result of igneous fusion; and that +in the cases of basalt and its congeners, they are being +extruded from volcanic vents at the present day. +The general principles for the classification of rocks +as recognised in modern science may be regarded as +having been finally established by James Hutton, of +Edinburgh, in his <i>Theory of the Earth</i>,<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> while they +were illustrated and defended by Professor Playfair in +his work entitled, <i>Illustrations of the Huttonian Theory +of the Earth</i>,<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a> although other observers, such as +Desmarest, Collini, and Guettard, had in other +countries come to very clear views on this subject.</p> + +<p>The following are some of the more important +works on the phenomena of volcanoes and earthquakes +published during the present century:—<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a></p> + +<p>1. Poulett Scrope, F.R.S., <i>Considerations on Volcanoes</i> +(1825). This work is dedicated to Lyell, his +fellow-worker in the same department of science, and +was undertaken, as he says, "in order to help to +dispel that signal delusion as to the mode of action +of the subtelluric forces with which the Elevation-Crater +theory had mystified the geological world." +The second edition was published in 1872.</p> + +<p><span class="pagenum"><a name="Page_6" id="Page_6">[Pg 6]</a></span></p><p>2. This was followed by the admirable work, <i>On +the Extinct Volcanoes of Central France</i>, published in +1826 (2nd edition, 1858), and is one of the most complete +monographs on a special volcanic district ever +written.</p> + +<p>3. Dr. Samuel Hibbert, <i>History of the Extinct Volcanoes +of the Basin of Neuwied on the Lower Rhine</i> +(1832). Dr. Hibbert's work is one of remarkable +merit, if we consider the time at which it was written. +For not only does it give a clear and detailed account +of the volcanic phenomena of the Eifel and the Lower +Rhine, but it anticipates the principles upon which +modern writers account for the formation of river +valleys and other physical features; and in working +out the physical history of the Rhine valley below +Mainz, and its connection with the extinct volcanoes +which are found on both banks of that river, he has +taken very much the same line of reasoning which +was some years afterwards adopted by Sir A. Ramsay +when dealing with the same subject. It does not +appear that the latter writer was aware of Dr. +Hibbert's treatise.</p> + +<p>4. Leopold von Buch, <i>Description Physique des Iles +Canaries</i> (1825), translated from the original by C. +Boulanger (1836); <i>Geognostische Reise</i> (Berlin, 1809), +2 vols.; and <i>Reise durch Italien</i> (1809). From a large +number of writings on volcanoes by this distinguished +traveller, whom Alexander von Humboldt calls "dem +geistreichen Forscher der Natur," the above are +selected as being the most important. That on the +Canaries is accompanied by a large atlas, in which +the volcanoes of Teneriffe, Palma, and Lancerote, +with some others, are elaborately represented, and +are considered to bear out the author's views regarding +<span class="pagenum"><a name="Page_7" id="Page_7">[Pg 7]</a></span>the formation of volcanic cones by elevation or +upheaval. The works dealing with the volcanic +phenomena of Central and Southern Italy are also +written with the object, in part at least, of illustrating +and supporting the same theoretical views; with +these we have to deal in the next chapter.</p> + +<p>5. Dr. Charles Daubeny, F.R.S., <i>Description of Active +and Extinct Volcanoes, of Earthquakes, and of Thermal +Springs, with remarks on the causes of these phenomena, +the character of their respective products, and their +influence on the past and present condition of the globe</i> +(2nd edition, 1848). In this work the author gives +detailed descriptions of almost all the known volcanic +districts of the globe, and defends what is called "the +chemical theory of volcanic action"—a theory at one +time held by Sir Humphrey Davy.</p> + +<p>6. Wolfgang Sartorius von Waltershausen, <i>Der +Ætna</i>. This work possesses a melancholy interest +from the fact that its distinguished author did not +live to see its publication. Von Waltershausen, having +spent several years in making an elaborate survey of +Etna, produced an atlas containing numerous detailed +maps, views, and drawings of this mountain and its +surroundings, which were published at Weimar by +Engelmann in 1858. A description in MS. to accompany +the atlas was also prepared, but before it was +printed, the author died, on the 16th October 1876. +The MS. having been put into the hands of the late +Professor Arnold von Lasaulx by the publisher of +the atlas, it was subsequently brought out under the +care of this distinguished petrologist, who was so +fully fitted for an undertaking of this kind.</p> + +<p>7. Sir Charles Lyell in his <i>Principles of Geology</i><a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> +<span class="pagenum"><a name="Page_8" id="Page_8">[Pg 8]</a></span>devotes several chapters to the consideration of +volcanic phenomena, in which, being in harmony +with the views of his friend, Poulett Scrope, he combats +the "elevation theory" of Von Buch, as applied +to the formation of volcanic mountains, holding that +they are built up of ashes, stones, and scoriæ blown +out of the throat of the volcano and piled around +the orifice in a conical form. Together with these +materials are sheets of lava extruded in a molten +condition from the sides or throat of the crater itself.</p> + +<p>8. Professor J. W. Judd, F.R.S., in his able work +entitled, <i>Volcanoes: What they are, and what they +teach</i>,<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> has furnished the student of vulcanicity with a +very complete manual of a general character on the +subject. The author, having extensive personal +acquaintance with the volcanoes of the south of +Europe and the volcanic rocks of the British Isles, +was well equipped for undertaking a work of the +kind; and in it he supports the views of Lyell and +Scrope regarding the mode of formation of volcanic +mountains.</p> + +<p>9. Sir Archibald Geikie, F.R.S., in his elaborate +monograph<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> on the Tertiary Volcanic Rocks of the +British Isles, has recorded his views regarding the +origin and succession of the plateau basalts and +associated rocks over the region extending from the +north of Ireland to the Inner Hebrides; and in +dealing with these districts in the following pages I +have made extensive use of his observations and +conclusions.</p> + +<p>10. <i>Report published by the Royal Society on the +Eruption of Krakatoa</i><span class="pagenum"><a name="Page_9" id="Page_9">[Pg 9]</a></span>—drawn up by several authors +(1885)—and the work on the same subject by Chev. +Verbeek, and published by the Government of the +Netherlands (1886). In these works all the phenomena +connected with the extraordinary eruptions of +Krakatoa in 1883 are carefully noted and scientifically +discussed, and illustrated by maps and drawings.</p> + +<p>11. <i>The Charleston Earthquake of August 31, 1886</i>, +by Captain Clarence Edward Dutton, U.S. Ordnance +Corps. Ninth Annual Report of the United States +Geological Survey, 1887-88, with maps and illustrations.</p> + +<p>12. Amongst other works which may be consulted +with advantage is that of Mr. T. Mellard Reade on +<i>The Origin of Mountain Ranges</i>; the Rev. Osmond +Fisher's <i>Physics of the Earth</i>; Professor G. H. +Darwin and Mr. C. Davison on "The Internal Tension +of the Earth's Crust," <i>Philosophical Transactions of the +Royal Society</i>, vol. 178; Mr. R. Mallet, "On the +Dynamics of Earthquakes," <i>Trans. Roy. Irish Academy</i>, +vol. xxi.; Professor O'Reilly's "Catalogues of Earthquakes," +<i>Trans. Roy. Irish Academy</i>, vol. xxviii. +(1884 and 1888); and Mr. A. Ent. Gooch <i>On the Causes +of Volcanic Action</i> (London, 1890). These and other +authorities will be referred to in the text.</p> + +<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> See Julius Schwarez <i>On the Failure of Geological Attempts made by +the Greeks</i>. (Edition 1888.)</p></div> + +<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a></p> +<div class="poem"> +<span class="i0">"Vidi ego, quod fuerat quondam solidissima tellus,<br /></span> +<span class="i0">Esse fretum. Vidi factas ex æquore terras:<br /></span> +<span class="i0">Et procul à pelago conchæ jacuere marinæ;<br /></span> +<span class="i0">Et vetus inventa est in montibus anchora sumnis.<br /></span> +<span class="i0">Quodque fuit campus, vallem de cursus aquarum<br /></span> +<span class="i0">Fecit; et eluvie mons est deductus in æquor:<br /></span> +<span class="i0">Eque paludosa siccis humus aret arenis;<br /></span> +<span class="i0">Quæque sitim tulerant, stagnata paludibus hument.<br /></span> +<span class="i0">Hic fontes Natura novos emissit, at illuc<br /></span> +<span class="i0">Clausit: et antiquis concussa tremoribus orbis<br /></span> +<span class="i0">Fulmina prosiliunt...."<br /></span> +</div> +<p style="margin-top:0em;"><span class="closing">—Lib. xv. 262.</span> +</p></div> + +<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a></p> +<div class="poem"> +<span class="i0">"Nec, quæ sulfureis ardet fornacibus, Ætne<br /></span> +<span class="i0">Ignea semper erit; neque enim fuit ignea semper.<br /></span> +<span class="i0">Nam, sive est animal tellus, et vivit, habetque<br /></span> +<span class="i0">Spiramenta locis flammam exhalantia multis;<br /></span> +<span class="i0">Spirandi mutare vias, quotiesque movetur,<br /></span> +<span class="i0">Has finire potest, illas aperire cavernas:<br /></span> +<span class="i0">Sive leves imis venti cohibentur in antris;<br /></span> +<span class="i0">Saxaque cum saxis...."<br /></span> +</div> +<p style="margin-top:0em;"><span class="closing">—<i>Ibid.</i>, 340.</span> +</p></div> + +<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> Strabo, lib. vi.</p></div> + +<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> Tacitus, lib. vi. 16, 20.</p></div> + +<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> <i>Principles of Geology</i>, 11th edition, vol. i., ch. 3.</p></div> + +<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> 2 vols., Edin. (1795).</p></div> + +<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> Edin. (1802).</p></div> + +<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> A more extended list of early works will be found in Daubeny's +<i>Volcanoes</i> (1848).</p></div> + +<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> 11th edition (1872).</p></div> + +<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> 4th edition (1888).</p></div> + +<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> "The History of Volcanic Action during the Tertiary Period in +the British Isles," <i>Trans. Roy. Soc., Edin.</i> Vol. xxxv, (1888).</p></div> +<p><span class="pagenum"><a name="Page_10" id="Page_10">[Pg 10]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_I_CHAPTER_II" id="PART_I_CHAPTER_II"></a>CHAPTER II. +<br /><br /> +FORM, STRUCTURE, AND COMPOSITION OF +VOLCANIC MOUNTAINS.</h2> + + +<p>The conical form of a volcanic mountain is so +generally recognised, that many persons who have no +intelligent acquaintance with geological phenomena +are in the habit of attributing to all mountains having +a conical form, and especially if accompanied by a +truncated apex, a volcanic origin. Yet this is very far +from being the fact, as some varieties of rock, such as +quartzite, not unfrequently assume this shape. Of +such we have an example in the case of Errigal, +a quartzite mountain in Donegal, nearly 3000 +feet high, which bears a very near approach in form +to a perfect cone or pyramid, and yet is in no way +connected, as regards its origin or structure, with +volcanic phenomena. Another remarkable instance +is that of Schehallion in Scotland, also composed +of quartz-rock; and others may be found amongst +the ranges of Islay and Jura, described by Sir A. +Geikie.<a name="FNanchor_1_13" id="FNanchor_1_13"></a><a href="#Footnote_1_13" class="fnanchor">[1]</a></p> + +<p>Notwithstanding, however, such exceptions, which +might be greatly multiplied, the majority of cone-shaped +mountains over the globe have a volcanic +<span class="pagenum"><a name="Page_11" id="Page_11">[Pg 11]</a></span>origin.<a name="FNanchor_2_14" id="FNanchor_2_14"></a><a href="#Footnote_2_14" class="fnanchor">[2]</a> The origin of this form in each case is +entirely distinct. In the case of quartzite mountains, +the conical form is due to atmospheric influences +acting on a rock of uniform composition, traversed by +numerous joints and fissures crossing each other at +obtuse angles, along which the rock breaks up and falls +away, so that the sides are always covered by angular +shingle forming slopes corresponding to the angle of +friction of the rock in question. In the case of a +volcanic mountain, however, the same form is due +either to accumulation of fragmental material piled +around the cup-shaped hollow, or crater, which is +usually placed at the apex of the cone, and owing +to which it is bluntly terminated, or else to the welling +up from beneath of viscous matter in the manner +presently to be described.</p> + +<p><i>Views of Sir Humphrey Davy and L. von Buch.</i>—The +question how a volcanic cone came to be +formed was not settled without a long controversy +carried on by several naturalists of eminence. Some +of the earlier writers of modern times on the subject +of vulcanicity—such as Sir Humphrey Davy and +Leopold von Buch—maintained that the conical +form was due to upheaval by a force acting from +below at a central focus, whereby the materials +of which the mountain is formed were forced to +assume a <i>quâ-quâ versal</i> position—that is, a position +in which the materials dip away from the central +focus in every direction. But this view, originally +<span class="pagenum"><a name="Page_12" id="Page_12">[Pg 12]</a></span>contested by Scrope and Lyell, has now been +generally abandoned. It will be seen on reflection +that if a series of strata of ashes, tuff, and lava, +originally horizontal, or nearly so, were to be forced +upwards into a conical form by a central force, the +result would be the formation of a series of radiating +fissures ever widening from the circumference towards +the focus. In the case of a large mountain such +fissures, whether filled with lava or otherwise, would +be of great breadth towards the focus, or central +crater, and could not fail to make manifest beyond +dispute their mechanical origin. But no fissures of +the kind here referred to are, as a matter of fact, to be +observed. Those which do exist are too insignificant +and too irregular in direction to be ascribed to such +an origin; so that the views of Von Buch and Davy +must be dismissed, as being unsupported by observation, +and as untenable on dynamical grounds. As a +matter of fact, the "elevatory theory," or the "elevation-crater +theory," as it is called by Scrope, has been +almost universally abandoned by writers on vulcanicity.</p> + +<p><i>Principal Varieties of Volcanic Mountains as regards +Form.</i>—But whilst rejecting the "elevatory theory," it +is necessary to bear in mind that volcanic cones and +dome-shaped elevations have been formed in several +distinct ways, giving rise to varieties of structure essentially +different. Two of the more general of these +varieties of form, the crater-cone and the dome, are +found in some districts, as in Auvergne, side by side. +The crater-cone consists of beds or sheets of ashes, +lapilli, and slag piled up in a conical form, with a central +crater (or cup) containing the principal pipe through +which these materials have been erupted; the dome, +<span class="pagenum"><a name="Page_13" id="Page_13">[Pg 13]</a></span>of a variety of trachytic lava, which has been extruded +in a molten, or viscous, condition from a central pipe, +and in such cases there is no distinct crater. There +are other forms of volcanic mountains, such as those +built up of basaltic matter, of which I shall have to +speak hereafter, but the two former varieties are the +most prevalent; and we may now proceed to consider +the conditions under which the crater-cone volcanoes +have been formed.</p> + +<p><i>Crateriform Volcanic Cones.</i>—Of this class nearly +all the active volcanoes of the Mediterranean region—Etna, +Vesuvius, Stromboli, and the Lipari Islands—may +be considered as representatives. They consist +essentially of masses of fragmental material, which +have from time to time been blown out of an orifice +and piled up around with more or less regularity +(according to the force exerted, and direction of +the prevalent winds), alternating with sheets of lava. +In this way mountains several thousand feet in height +and of vast horizontal extent are formed. The fragmental +materials thus accumulated are of all sizes, +from the finest dust up to blocks many tons in weight, +the latter being naturally piled around nearest to +the orifice. The fine dust, blown high into the air +by the explosive force of the gases and vapours, is +often carried to great distances by the prevalent +winds. Thus during the eruption of Vesuvius in <span class="smcap">A.D.</span> +472 showers of ashes, carried high into the air by the +westerly wind, fell over Constantinople at a distance +of 750 miles.<a name="FNanchor_3_15" id="FNanchor_3_15"></a><a href="#Footnote_3_15" class="fnanchor">[3]</a></p> + +<p><span class="pagenum"><a name="Page_14" id="Page_14">[Pg 14]</a></span></p><p>These loose, or partially consolidated, fragmental +materials are rudely stratified, and slope downwards +and outwards from the edge of the crater, so as to +present the appearance of what is known as "the +dip" of stratified deposits which have been upraised +from the horizontal position by terrestrial forces. It +was this excentrical arrangement which gave rise to +the supposition that such volcanic ash-beds had been +tilted up by a force acting in the direction of the +volcanic throat, or orifice of eruption. The interior +wall of Monte di Somma, the original crater of +Vesuvius, presents a good illustration of such fragmental +beds. I shall have occasion further on to +describe more fully the structure of this remarkable +mountain; so that it will suffice to say here that this +old prehistoric crater, the walls of which enclose the +modern cone of Vesuvius, is seen to be formed of +irregular beds of ash, scoriæ, and fragmental masses, +traversed by numerous dykes of lava, and sloping +away outwards towards the surrounding plains.</p> + +<p>Of similar materials are the flanks of Etna composed, +even at great distances from the central crater; +the beds of ash and agglomerate sometimes alternating +with sheets of solidified lava and traversed +by dykes of similar material of later date, injected +from below through fissures formed during periods of +eruptive energy. Numerous similar examples are to +be observed in the Auvergne region of Central France +and the Eifel. And here we find remarkable cases of +"breached cones," or craters, which will require some +special description. Standing on the summit of the +Puy de Dôme, and looking northwards or southwards, +the eye wanders over a tract formed of dome-shaped +hills and of extinct crater-cones rising from +<span class="pagenum"><a name="Page_15" id="Page_15">[Pg 15]</a></span>a granitic platform. But what is most peculiar in +the scene is the ruptured condition of a large number +of the cones with craters. In such cases the wall of +the crater has been broken down on one side, and we +observe that a stream of lava has been poured out +through the breach and overflowed the plain below. +The cause of this breached form is sufficiently obvious. +In such cases there has been an explosion of ashes, +stones, and scoriæ from the volcanic throat, by which +a cone-shaped hill with a crater has been built up. +This has been followed by molten lava welling up +through the throat, and gradually filling the crater. +But, as the lava is much more dense than the material +of which the crater wall is composed, the pressure +of the lava outwards has become too great for the +resistance of the wall, which consequently has given +way at its weakest part and, a breach being formed, +the molten matter has flowed out in a stream which +has inundated the country lying at the base of the +cone. In one instance mentioned by Scrope, the +original upper limit of the lake of molten lava has +left its mark in the form of a ring of slag on the +inside of the breached crater.<a name="FNanchor_4_16" id="FNanchor_4_16"></a><a href="#Footnote_4_16" class="fnanchor">[4]</a></p> + +<p><i>Craterless Domes.</i>—These differ essentially both in +form and composition from those just described, +and have their typical representatives in the +Auvergne district, though not without their analogues +elsewhere, as in the case of Chimborazo, in +South America, one of the loftiest volcanic mountains +in the world.</p> + +<p><span class="pagenum"><a name="Page_16" id="Page_16">[Pg 16]</a></span></p> +<div class="figcenter"> +<a name="FIGURE_2"> + <img src="images/figure2.jpg" alt="Cotopaxi" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 2.</span>—Cotopaxi, a volcano of the Cordilleras of Quito, still active, +and covered by snow down to a level of 14,800 feet. Below this is a +zone of naked rock, succeeded by another of forest vegetation. Owing +to the continuous extrusion of lava from the crater, the cone is being +gradually built up of fresh material, and the crater is comparatively small +in consequence.—(A diagrammatic view after A. von Humboldt.) +</td></tr> +</table> +</div> + +<p>Taking the Puy de Dôme, Petit Suchet, Cliersou, +Grand Sarcoui in Auvergne, and the Mamelon in the +Isle of Bourbon as illustrations, we have in all these +cases a group of volcanic hills, dome-shaped and +destitute of craters, the summits being rounded or +slightly flattened. We also observe that the flanks +rise more abruptly from their bases, and contrast in +outline with the graceful curve of the crater cones. +<span class="pagenum"><a name="Page_17" id="Page_17">[Pg 17]</a></span>The dome-shaped volcanoes are generally composed of +felsitic matter, whether domite, trachyte, or andesite, +which has been extruded in a molten or viscous +condition from some orifice or fissure in the earth's +crust, and being piled up and spreading outwards, +necessarily assumes such a form as that of a dome, +as has been shown by experiment on a small scale by +Dr. E. Reyer, of Grätz.<a name="FNanchor_5_17" id="FNanchor_5_17"></a><a href="#Footnote_5_17" class="fnanchor">[5]</a> The contrast between the +two forms (those of the dome and the crater-cone) is +exemplified in the case of the Grand Sarcoui and its +neighbours. The former is composed of a species of +trachyte; the latter of ashes and fragmental matter +which have been blown out of their respective vents of +eruption into the air, and piled up and around in a +crateriform manner with sides of gradually diminishing +slope outwards, thus giving rise to the characteristic +volcanic curve. The two varieties here +referred to, contrasting in form, composition, and +colour of material, can be clearly recognised from the +summit of the Puy de Dôme, which rises by a head +and shoulders above its fellows, and thus affords an +advantageous standpoint from which to compare the +various forms of this remarkable group of volcanic +mountains.</p> + +<p>Cotopaxi (<a href="#FIGURE_2">Fig. 2</a>) has been generally supposed to be +a dome; but Whymper, who ascended the mountain +in 1880, shows that it is a cone with a crater, 2,300 +feet in largest diameter. He determined the height to +be 19,613 feet above the ocean. Its real elevation +above the sea is somewhat masked, owing to the fact +that it rises from the high plain of Tapia, which is +<span class="pagenum"><a name="Page_18" id="Page_18">[Pg 18]</a></span>itself 8,900 feet above the sea surface. The smaller +peak on the right (<a href="#FIGURE_2">Fig. 2</a>) is that of Carihuairazo, +which reaches an elevation of over 16,000 feet.</p> + +<p>Chimborazo, in Columbia, province of Quito, is one +of the loftiest of the chain of the Andes, and is +situated in lat. 1° 30' S., long. 78° 58' W. Though not +in a state of activity, it is wholly composed of volcanic +material, and reaches an elevation of over 20,000 feet +above the ocean; its sides being covered by a sheet +of permanent snow to a level of 2,600 feet below the +summit.<a name="FNanchor_6_18" id="FNanchor_6_18"></a><a href="#Footnote_6_18" class="fnanchor">[6]</a> Seen from the shores of the Pacific, after +the long rains of winter, it presents a magnificent +spectacle, "when the transparency of the air is +increased, and its enormous circular summit is seen +projected upon the deep azure blue of the equatorial +sky. The great rarity of the air through which the +tops of the Andes are seen adds much to the splendour +of the snow, and aids the magical effect of its +reflection."</p> + +<p>Chimborazo was ascended by Humboldt and Bonpland +in 1802 almost to the summit; but at a height +of 19,300 feet by barometrical measurement, their +further ascent was arrested by a wide chasm. Boussingault, +in company with Colonel Hall, accomplished +the ascent as far as the foot of the mass of columnar +"trachyte," the upper surface of which, covered +by a dome of snow, forms the summit of the mountain. +The whole mass of the mountain consists +of volcanic rock, varieties of andesite; there is no +trace of a crater, nor of any fragmental materials, +<span class="pagenum"><a name="Page_19" id="Page_19">[Pg 19]</a></span>such as are usually ejected from a volcanic vent of +eruption.<a name="FNanchor_7_19" id="FNanchor_7_19"></a><a href="#Footnote_7_19" class="fnanchor">[7]</a></p> + +<p><i>Lava Crater-Cones.</i>—A third form of volcanic +mountain is that which has been built up by successive +eruptions of basic lava, such as basalt or dolerite, +when in a molten condition. These are very rare, +and the slope of the sides depends on the amount of +original viscosity. Where the lava is highly fused its +slope will be slight, but if in a viscous condition, +successive outpourings from the orifice, unable to +reach the base of the mountain, will tend to form a +cone with increasing slope upwards. Mauna Loa +and Kilauea, in the Hawaiian Group, according to +Professor J. D. Dana, are basalt volcanoes in a normal +state. They have distinct craters, and the material +of which the mountain is formed is basalt or dolerite. +The volcano of Rangitoto in Auckland, New Zealand, +appears to belong to this class.</p> + +<p>Basalt is the most fusible of volcanic rocks, owing +to the augite and magnetite it contains, so that it +spreads out with a very slight slope when highly +fused. Trachyte, on the other hand, is the least +fusible owing to the presence of orthoclase felspar, or +quartz; so that the volcanic domes formed of this +material stand at a higher angle from the horizon +than those of basaltic cones.</p> + +<div class="footnote"><p><a name="Footnote_1_13" id="Footnote_1_13"></a><a href="#FNanchor_1_13"><span class="label">[1]</span></a> <i>Scenery and Geology of Scotland</i> (1865), p. 214.</p></div> + +<div class="footnote"><p><a name="Footnote_2_14" id="Footnote_2_14"></a><a href="#FNanchor_2_14"><span class="label">[2]</span></a> Humboldt says: "The form of isolated conical mountains, as +those of Vesuvius, Etna, the Peak of Teneriffe, Tunguagua, and +Cotopaxi, is certainly the shape most commonly observed in volcanoes +all over the globe."—<i>Views of Nature</i>, translated by E. C. Otté and +H. G. Bohn (1850).</p></div> + +<div class="footnote"><p><a name="Footnote_3_15" id="Footnote_3_15"></a><a href="#FNanchor_3_15"><span class="label">[3]</span></a> It is supposed that after the disastrous explosion of Krakatoa in +1883 the fine dust carried into the higher regions of the atmosphere +was carried round almost the entire globe, and remained suspended for +a lengthened period, as described in a future page.</p></div> + +<div class="footnote"><p><a name="Footnote_4_16" id="Footnote_4_16"></a><a href="#FNanchor_4_16"><span class="label">[4]</span></a> Another remarkable case is mentioned and figured by Judd, where +one of the Lipari Isles, composed of pumice and rising out of the +Mediterranean, has been breached by a lava-stream of obsidian.—<i>Loc. +cit.</i>, p. 123.</p></div> + +<div class="footnote"><p><a name="Footnote_5_17" id="Footnote_5_17"></a><a href="#FNanchor_5_17"><span class="label">[5]</span></a> Reyer has produced such dome-shaped masses by forcing a quantity +of plaster of Paris in a pasty condition up through an orifice in a board; +referred to by Judd, <i>loc. cit.</i>, p. 125.</p></div> + +<div class="footnote"><p><a name="Footnote_6_18" id="Footnote_6_18"></a><a href="#FNanchor_6_18"><span class="label">[6]</span></a> Whymper determined the height to be 20,498 feet; Reiss and +Stübel make it 20,703 feet. Whymper thinks there may be a crater +concealed beneath the dome of snow.—<i>Travels amongst the Great +Andes of the Equator</i>, by Edward Whymper (1892).</p></div> + +<div class="footnote"><p><a name="Footnote_7_19" id="Footnote_7_19"></a><a href="#FNanchor_7_19"><span class="label">[7]</span></a> Whymper states that there is a prevalent idea that Cotopaxi and a +volcano called Sangai act as safety-valves to each other. Sangai reaches +an elevation (according to Reiss and Stübel) of 17,464 feet, and sends +intermittent jets of steam high into the air, spreading out into vast +cumulus clouds, which float away southwards, and ultimately disappear.—<i>Ibid.</i>, +p. 73.</p></div> +<p><span class="pagenum"><a name="Page_20" id="Page_20">[Pg 20]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_I_CHAPTER_III" id="PART_I_CHAPTER_III"></a>CHAPTER III. +<br /><br /> +LINES AND GROUPS OF ACTIVE VOLCANIC VENTS.</h2> + + +<p>The globe is girdled by a chain of volcanic +mountains in a state of greater or less activity, which +may perhaps be considered a girdle of safety for the +whole world, through which the masses of molten +matter in a state of high pressure beneath the crust +find a way of escape; and thus the structure of the +globe is preserved from even greater convulsions than +those which from time to time take place at various +points on its surface. This girdle is partly terrestrial, +partly submarine; and commencing at Mount Erebus, +near the Antarctic Pole, ranging through South +Shetland Isle, Cape Horn, the Andes of South +America, the Isthmus of Panama, then through +Central America and Mexico, and the Rocky Mountains +to Kamtschatka, the Aleutian Islands, the +Kuriles, the Japanese, the Philippines, New Guinea, +and New Zealand, reaches the Antarctic Circle by the +Balleny Islands. This girdle sends off branches at +several points. (See <a href="#MAP_1">Map, p. 23</a>.)</p> + +<p><span class="pagenum"><a name="Page_21" id="Page_21">[Pg 21]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_3"> + <img src="images/figure3.jpg" alt="Volcanic cone of Orizaba" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 3.</span>—Volcanic cone of Orizaba (Cittaltepeth), in Mexico, now +extinct; the upper part snow-clad, and at its base forest vegetation; it +reaches a height of 16,302 Parisian feet above the sea.—(After A. von +Humboldt.) +</td></tr> +</table> +</div> + + +<p>(<i>a.</i>) The linear arrangement of active or dormant +volcanic vents has been pointed out by Humboldt, +Von Buch, Daubeny, and other writers. The great +range of burning mountains of the Andes of Chili, +Peru, Bolivia, and Mexico, that of the Aleutian +Islands, of Kamtschatka and the Kurile Islands, +extending southwards into the Philippines, and the +branching range of the Sunda Islands are well-known +examples. That of the West Indian Islands, +ranging from Grenada through St. Vincent, St. +Lucia, Martinique, Dominica, Guadeloupe, Montserrat, +Nevis, and St. Eustace,<a name="FNanchor_1_20" id="FNanchor_1_20"></a><a href="#Footnote_1_20" class="fnanchor">[1]</a> is also a remarkable +example of the linear arrangement of volcanic +<span class="pagenum"><a name="Page_22" id="Page_22">[Pg 22]</a></span>mountains. On tracing these ranges on a map +of the world<a name="FNanchor_2_21" id="FNanchor_2_21"></a><a href="#Footnote_2_21" class="fnanchor">[2]</a> (<a href="#MAP_1">Map, p. 23</a>), it will be observed +that they are either strings of islands, or lie in +proximity to the ocean; and hence the view was +naturally entertained by some writers that oceanic +water, or at any rate that of a large lake or sea, +was a necessary agent in the production of volcanic +eruptions. This view seems to receive further corroboration +from the fact that the interior portions +of the continents and large islands such as Australia +are destitute of volcanoes in action, with the remarkable +exceptions of Mounts Kenia and Kilimanjaro in +Central Africa, and a few others. It is also very +significant in this connection that many of the +volcanoes now extinct, or at least dormant, both in +Europe and Asia, appear to have been in proximity +to sheets of water during the period of activity. +Thus the old volcanoes of the Haurân, east of the +Jordan, appear to have been active at the period +when the present Jordan valley was filled with water +to such an extent as to constitute a lake two hundred +miles in length, but which has now shrunk back to +within the present limits of the Dead Sea.<a name="FNanchor_3_22" id="FNanchor_3_22"></a><a href="#Footnote_3_22" class="fnanchor">[3]</a> Again, +at the period when the extinct volcanoes of Central +France were in active operation, an extensive lake +overspread the tract lying to the east of the granitic +plateau on which the craters and domes are planted, +now constituting the rich and fertile plain of Clermont.</p> + +<p><span class="pagenum"><a name="Page_23" id="Page_23">[Pg 23]</a></span></p> + +<div class="figcenter"> +<a name="MAP_1"></a> +<a href="images/map1full.jpg"> + <img src="images/map1.jpg" alt="Map of Volcanoes" /> +</a> +</div> + +<p>Such instances are too significant to allow us to +<span class="pagenum"><a name="Page_24" id="Page_24">[Pg 24]</a></span>doubt that water in some form is very generally +connected with volcanic operations; but it does not +follow that it was necessary to the original formation +of volcanic vents, whether linear or sporadic. If +this were so, the extinct volcanoes of the British +Isles would still be active, as they are close to the +sea-margin, and no volcano would now be active +which is not near to some large sheet of water. +But Jorullo, one of the great active volcanoes of +Mexico, lies no less than 120 miles from the ocean, +and Cotopaxi, in Ecuador, is nearly equally distant. +Kilimanjaro, 18,881 feet high, and Kenia, in the +equatorial regions of Central Africa, are about 150 +miles from the Victoria Nyanza, and a still greater +distance from the ocean; and Mount Demavend, in +Persia, which rises to an elevation of 18,464 feet near +the southern shore of the Caspian Sea, a volcanic +mountain of the first magnitude, is now extinct or +dormant.<a name="FNanchor_4_23" id="FNanchor_4_23"></a><a href="#Footnote_4_23" class="fnanchor">[4]</a> Such facts as these all tend to show that +although water may be an accessory of volcanic +eruptions, it is not in all cases essential; and we +are obliged, therefore, to have recourse to some other +theory of volcanic action differing from that which +would attribute it to the access of water to highly +heated or molten matter within the crust of the earth.</p> + +<p>(<i>b.</i>) <i>Leopold von Buch on Rents and Fissures in the +Earth's Crust.</i>—The view of Leopold von Buch, who +considered that the great lines of volcanic mountains +above referred to rise along the borders of rents, or +fissures, in the earth's crust, is one which is inherently +<span class="pagenum"><a name="Page_25" id="Page_25">[Pg 25]</a></span>probable, and is in keeping with observation. That +the crust of the globe is to a remarkable extent +fissured and torn in all directions is a phenomenon +familiar to all field geologists. Such rents and fissures +are often accompanied by displacement of the strata, +owing to which the crust has been vertically elevated +on one side or lowered on the other, and such displacements +(or "faults") sometimes amount to thousands +of feet. It is only occasionally, however, that such +fractures are accompanied by the extrusion of molten +matter; and in the North of England and Scotland +dykes of igneous rock, such as basalt, which run +across the country for many miles in nearly straight +lines, often cut across the faults, and are only rarely +coincident with them. Nevertheless, it can scarcely +be a question that the grand chain of volcanic +mountains which stretches almost continuously along +the Andes of South America, and northwards through +Mexico, has been piled up along the line of a system +of fissures in the fundamental rocks parallel to the +coast, though not actually coincident therewith.</p> + +<p>(<i>c.</i>) <i>The Cordilleras of Quito.</i>—The structure and +arrangement of the Cordilleras of Quito, for example, +are eminently suggestive of arrangement along lines +of fissure. As shown by Alexander von Humboldt,<a name="FNanchor_5_24" id="FNanchor_5_24"></a><a href="#Footnote_5_24" class="fnanchor">[5]</a> +the volcanic mountains are disposed in two parallel +chains, which run side by side for a distance of over +500 miles northwards into the State of Columbia, and +enclose between them the high plains of Quito and +Lacunga. Along the eastern chain are the great +cones of El Altar, rising to an elevation of 16,383 +feet above the ocean, and having an enormous crater +apparently dormant or extinct, and covered with snow; +<span class="pagenum"><a name="Page_26" id="Page_26">[Pg 26]</a></span>then Cotopaxi (<a href="#FIGURE_2">Fig. 2</a>), its sides covered with snow, +and sending forth from its crater several columns of +smoke; then Guamani and Cayambe (19,000 feet), huge +truncated cones apparently extinct; these constitute +the eastern chain of volcanic heights. The western +chain contains even loftier mountains. Here we find +the gigantic Chimborazo, an extinct volcano whose +summit is white with snow; Carihuairazo<a name="FNanchor_6_25" id="FNanchor_6_25"></a><a href="#Footnote_6_25" class="fnanchor">[6]</a> and Illiniza, +a lofty pointed peak like the Matterhorn; Corazon, a +snow-clad dome, reaching a height of 15,871 feet; +Atacazo and Pichincha, the latter an extinct volcano +reaching an elevation of 15,920 feet; such is the +western chain, remarkable for its straightness, the +volcanic cones being planted in one grand procession +from south to north. This rectilinear arrangement of +the western chain, only a little less conspicuous in the +eastern, is very suggestive of a line of fracture +in the crust beneath. And when we contemplate +the prodigious quantity of matter included +within the limits of these colossal domes and their +environments, all of which has been extruded from the +internal reservoirs, we gain some idea of the manner +in which the contracting crust disposes of the matter +it can no longer contain.<a name="FNanchor_7_26" id="FNanchor_7_26"></a><a href="#Footnote_7_26" class="fnanchor">[7]</a></p> + +<p>Between the volcanoes of Quito and those of Peru +there is an intervening space of fourteen degrees of +<span class="pagenum"><a name="Page_27" id="Page_27">[Pg 27]</a></span>latitude. This is occupied by the Andes, regarding +the structure of which we have not much information +except that at this part of its course it is not volcanic. +But from Arequipa in Peru (lat. 16° S.), an active +volcano, we find a new series of volcanic mountains +continued southwards through Tacora (19,740 feet), +then further south the more or less active vents of +Sajama (22,915 feet), Coquina, Tutupaca, Calama, +Atacama, Toconado, and others, forming an almost +continuous range with that part of the desert of +Atacama pertaining to Chili. Through this country +we find the volcanic range appearing at intervals; +and still more to the southwards it is doubtless connected +with the volcanoes of Patagonia, north of the +Magellan Straits, and of Tierra del Fuego. Mr. +David Forbes considers that this great range of +volcanic mountains, lying nearly north and south, +corresponds to a line of fracture lying somewhat to +the east of the range.<a name="FNanchor_8_27" id="FNanchor_8_27"></a><a href="#Footnote_8_27" class="fnanchor">[8]</a></p> + +<p>(<i>d.</i>) <i>Other Volcanic Chains.</i>—A similar statement in +all probability applies to the systems of volcanic mountains +of the Aleutian Isles, Kamtschatka, the Kuriles, +the Philippines, and Sunda Isles. Nor can it be +reasonably doubted that the western American coast-line +has to a great extent been determined, or marked +out, by such lines of displacement; for, as Darwin +has shown, the whole western coast of South America, +for a distance of between 2000 and 3000 miles south +<span class="pagenum"><a name="Page_28" id="Page_28">[Pg 28]</a></span>of the Equator, has undergone an upward movement +in very recent times—that is, within the period of +living marine shells—during which period the volcanoes +have been in activity.<a name="FNanchor_9_28" id="FNanchor_9_28"></a><a href="#Footnote_9_28" class="fnanchor">[9]</a></p> + +<p>(<i>e.</i>) <i>The Kurile Islands.</i>—This chain may also be +cited in evidence of volcanic action along fissure lines. +It connects the volcanoes of Kamtschatka with those +of Japan, and the linear arrangement is apparent. In +the former peninsula Erman counted no fewer than +thirteen active volcanic mountains rising to heights +of 12,000 to 15,000 feet above the sea.<a name="FNanchor_10_29" id="FNanchor_10_29"></a><a href="#Footnote_10_29" class="fnanchor">[10]</a> In the chain +of the Kuriles Professor John Milne counted fifty-two +well-defined volcanoes, of which nine, perhaps more, +are certainly active.<a name="FNanchor_11_30" id="FNanchor_11_30"></a><a href="#Footnote_11_30" class="fnanchor">[11]</a> They are not so high as those +of Kamtschatka; but, on the other hand, they rise +from very deep oceanic waters, and have been +probably built up from the sea bottom by successive +eruptions of tuff, lava, and ash. According to the +view of Professor Milne, the volcanoes of the Kurile +chain are fast becoming extinct.</p> + +<p>(<i>f.</i>) <i>Volcanic Groups.</i>—Besides the volcanic vents +arranged in lines, of which we have treated above, +there are a large number, both active and extinct, +which appear to be disposed in groups, or sporadically +distributed, over various portions of the earth's surface. +I say <i>appear to be</i>, because this sporadic +distribution may really be resolvable (at least in +some cases) into linear distribution for short distances. +Thus the Neapolitan Group, which might +<span class="pagenum"><a name="Page_29" id="Page_29">[Pg 29]</a></span>at first sight seem to be arranged round Vesuvius as +a centre, really resolves itself into a line of active and +extinct vents of eruption, ranging across Italy from +the Tyrrhenian Sea to the Adriatic, through Ischia, +Procida, Monte Nuovo and the Phlegræan Fields, +Vesuvius, and Mount Vultur.<a name="FNanchor_12_31" id="FNanchor_12_31"></a><a href="#Footnote_12_31" class="fnanchor">[12]</a> Again, the extinct +volcanoes of Central France, which appear to form +an isolated group, indicate, when viewed in detail, +a linear arrangement ranging from north to south.<a name="FNanchor_13_32" id="FNanchor_13_32"></a><a href="#Footnote_13_32" class="fnanchor">[13]</a> +Another region over which extinct craters are distributed +lies along the banks of the Rhine, above +Bonn and the Moselle; a fourth in Hungary; a fifth +in Asia Minor and Northern Palestine; and a sixth +in Central Asia around Lake Balkash. These are +all continental, and the linear distribution is not +apparent.</p> + +<div class="footnote"><p><a name="Footnote_1_20" id="Footnote_1_20"></a><a href="#FNanchor_1_20"><span class="label">[1]</span></a> For an interesting account of this range of volcanic islands see +Kingsley's <i>At Last</i>. The grandest volcanic peak is that of Guadeloupe, +rising to a height of 5000 feet above the ocean, amidst a group +of fourteen extinct craters. But the most active vent of the range is +the Souffrière of St. Vincent. In the eruption of 1812 this mountain +sent forth clouds of pumice, scoriæ and ashes, some of which were +carried by an upper counter current to Barbados, one hundred miles to +the eastward, covering the surface with volcanic dust to a depth of +several inches.</p></div> + +<div class="footnote"><p><a name="Footnote_2_21" id="Footnote_2_21"></a><a href="#FNanchor_2_21"><span class="label">[2]</span></a> An excellent, and perhaps the most recent, map of this kind is that +given by Professor Prestwich in his <i>Geology</i>, vol. i. p. 216. One on a +larger scale is that by Keith Johnston in his <i>Physical Atlas</i>.</p></div> + +<div class="footnote"><p><a name="Footnote_3_22" id="Footnote_3_22"></a><a href="#FNanchor_3_22"><span class="label">[3]</span></a> <i>Memoir on the Physical Geology and Geography of Arabia Petræa, +Palestine</i>, etc., published for the Committee of the Palestine Exploration +Fund (1886), p. 113, etc.</p></div> + +<div class="footnote"><p><a name="Footnote_4_23" id="Footnote_4_23"></a><a href="#FNanchor_4_23"><span class="label">[4]</span></a> This mountain was ascended in 1837 by Mr. Taylor Thomson, who +found the summit covered with sulphur, and from a cone fumes at a +high temperature issued forth, but there was no eruption.—<i>Journ. Roy. +Geographical Soc.</i>, vol. viii. p. 109.</p></div> + +<div class="footnote"><p><a name="Footnote_5_24" id="Footnote_5_24"></a><a href="#FNanchor_5_24"><span class="label">[5]</span></a> Humboldt, <i>Atlas der Kleineren Schriften</i> (1853).</p></div> + +<div class="footnote"><p><a name="Footnote_6_25" id="Footnote_6_25"></a><a href="#FNanchor_6_25"><span class="label">[6]</span></a> Ascended by Whymper June 29, 1880. He found the elevation to +be 16,515 feet.</p></div> + +<div class="footnote"><p><a name="Footnote_7_26" id="Footnote_7_26"></a><a href="#FNanchor_7_26"><span class="label">[7]</span></a> The arrangement of the volcanoes of Peru and Bolivia is also suggestive +of a double line of fissure, while those of Chili suggest one +single line. The volcanoes of Arequipa, in the southern part of Peru, +are dealt with by Dr. F. H. Hatch, in his inaugural dissertation, +<i>Ueber die Gesteine der Vulcan-Gruppe von Arequipa</i> (Wien, 1886). +The volcanoes rise to great elevations, having their summits capped by +snow. The volcano of Charchani, lying to the north of Arequipa, +reaches an elevation of 18,382 Parisian feet. That of Pichupichu +reaches a height of 17,355 Par. feet. The central cone of Misti has +been variously estimated to range from 17,240 to 19,000 Par. feet. +The rocks of which the mountains are composed consist of varieties of +andesite.</p></div> + +<div class="footnote"><p><a name="Footnote_8_27" id="Footnote_8_27"></a><a href="#FNanchor_8_27"><span class="label">[8]</span></a> D. Forbes, "On the Geology of Bolivia and Southern Peru," +<i>Quarterly Journal of the Geological Society</i>, vol. xvii. p. 22 (1861).</p></div> + +<div class="footnote"><p><a name="Footnote_9_28" id="Footnote_9_28"></a><a href="#FNanchor_9_28"><span class="label">[9]</span></a> Darwin, <i>Structure and Distribution of Coral Reefs</i>, second edition, +p. 186.</p></div> + +<div class="footnote"><p><a name="Footnote_10_29" id="Footnote_10_29"></a><a href="#FNanchor_10_29"><span class="label">[10]</span></a> Erman, <i>Reise um die Welt</i>.</p></div> + +<div class="footnote"><p><a name="Footnote_11_30" id="Footnote_11_30"></a><a href="#FNanchor_11_30"><span class="label">[11]</span></a> Milne, "Cruise amongst the Kurile Islands," <i>Geol. Mag.</i>, New +Ser. (August 1879).</p></div> + +<div class="footnote"><p><a name="Footnote_12_31" id="Footnote_12_31"></a><a href="#FNanchor_12_31"><span class="label">[12]</span></a> See Daubeny, <i>Volcanoes</i>, Map I.</p></div> + +<div class="footnote"><p><a name="Footnote_13_32" id="Footnote_13_32"></a><a href="#FNanchor_13_32"><span class="label">[13]</span></a> Sir A. Geikie has connected as a line of volcanic vents those of +Sicily, Italy, Central France, the N. E. of Ireland, the Inner Hebrides +and Iceland, of which the central vents are extinct or dormant, the +extremities active.</p></div> +<p><span class="pagenum"><a name="Page_30" id="Page_30">[Pg 30]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_I_CHAPTER_IV" id="PART_I_CHAPTER_IV"></a>CHAPTER IV. +<br /><br /> +MID-OCEAN VOLCANIC ISLANDS.</h2> + + +<p><i>Oceanic Islands.</i>—By far the most extensive regions +with sporadically distributed volcanic vents, both +active and extinct, are those which are overspread +by the waters of the ocean, where the vents emerge +in the form of islands. These are to be found +in all the great oceans, the Atlantic, the Pacific, and +the Indian; but are especially numerous over the +central Pacific region. As Kotzebue and subsequently +Darwin have pointed out, all the islands of +the Pacific are either coral-reefs or of volcanic origin; +and many of these rise from great depths; that is to +say, from depths of 1000 to 2000 fathoms. It is +unnecessary here to attempt to enumerate all these +islands which rise in solitary grandeur from the surface +of the ocean, and are the scenes of volcanic operations; +a few may, however, be enumerated.</p> + +<p><span class="pagenum"><a name="Page_31" id="Page_31">[Pg 31]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_4"> + <img src="images/figure4.jpg" alt="Teneriffe from ocean" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 4.</span>—The Peak of Teneriffe (Pic de Teyde) as seen from the ocean.—(From a photograph.) +</td></tr> +</table> +</div> + +<p>(<i>a.</i>) <i>Iceland.</i>—In the Atlantic, Iceland first claims +notice, owing to the magnitude and number of its +active vents and the variety of the accompanying +phenomena, especially the geysers. As Lyell has +observed,<a name="FNanchor_1_33" id="FNanchor_1_33"></a><a href="#Footnote_1_33" class="fnanchor">[1]</a> with the exception of Etna and Vesuvius, +the most complete chronological records of a series of +<span class="pagenum"><a name="Page_32" id="Page_32">[Pg 32]</a></span>eruptions in existence are those of Iceland, which +come down from the ninth century of our era, and +which go to show that since the twelfth century there +has never been an interval of more than forty years +without either an eruption or a great earthquake. +So intense is the volcanic energy in this island that +some of the eruptions of Hecla have lasted six years +without cessation. Earthquakes have often shaken +the whole island at once, causing great changes in +the interior, such as the sinking down of hills, the +rending of mountains, the desertion by rivers of their +channels, and the appearance of new lakes. New +islands have often been thrown up near the coast, +while others have disappeared. In the intervals +between the eruptions, innumerable hot springs +afford vent to the subterranean heat, and solfataras +discharge copious streams of inflammable +matter. The volcanoes in different parts of the +island are observed, like those of the Phlegræan +Fields, to be in activity by turns, one vent serving for +a time as a safety-valve for the others. The most +memorable eruption of recent years was that of +Skaptár Jokul in 1783, when a new island was thrown +up, and two torrents of lava issued forth, one 45 and +the other 50 miles in length, and which, according to +the estimate of Professor Bischoff, contained matter +surpassing in magnitude the bulk of Mont Blanc. +One of these streams filled up a large lake, and, +entering the channel of the Skaptâ, completely dried +up the river. The volcanoes of Iceland may be considered +as safety-valves to the region in which lie the +British Isles.</p> + +<p>(<i>b.</i>) <i>The Azores, Canary, and Cape de Verde Groups.</i>—This +group of volcanic isles rises from deep Atlantic +<span class="pagenum"><a name="Page_33" id="Page_33">[Pg 33]</a></span>waters north of the Equator, and the vents of eruption +are partially active, partially dormant, or extinct. It +must be supposed, however, that at a former period +volcanic action was vastly more energetic than at +present; for, except at the Grand Canary, Gomera, +Forta Ventura, and Lancerote, where various non-volcanic +rocks are found, these islands appear to have +been built up from their foundations of eruptive +materials. The highest point in the Azores is the +Peak of Pico, which rises to a height of 7016 feet +above the ocean. But this great elevation is surpassed +by that of the Peak of Teneriffe (or Pic de +Teyde) in the Canaries, which attains to an elevation +of 12,225 feet, as determined by Professor Piazzi +Smyth.<a name="FNanchor_2_34" id="FNanchor_2_34"></a><a href="#Footnote_2_34" class="fnanchor">[2]</a></p> + +<p>This great volcanic cone, rising from the ocean, +its summit shrouded in snow, and often protruding +above the clouds, must be an object of uncommon +beauty and interest when seen from the deck of a +ship. (<a href="#FIGURE_4">Fig. 4</a>.) The central cone, formed of trachyte, +pumice, obsidian, and ashes, rises out of a vast caldron +of older basaltic rocks with precipitous inner walls—much +as the cone of Vesuvius rises from within the +partially encircling walls of Somma. (<a href="#FIGURE_5">Fig. 5</a>.) From +the summit issue forth sulphurous vapours, but no +flame.</p> + +<p>Piazzi Smyth, who during a prolonged visit to this +mountain in 1856 made a careful survey of its form +and structure, shows that the great cone is surrounded +by an outer ring of basalt enclosing two <i>foci</i> of eruption, +<span class="pagenum"><a name="Page_34" id="Page_34">[Pg 34]</a></span>the lavas from which have broken through the ring +of the outer crater on the western side, and have +poured down the mountain. At the top of the peak +its once active crater is filled up, and we find a +convex surface ("The Plain of Rambleta") surmounted +towards its eastern end by a diminutive +cone, 500 feet high, called "Humboldt's Ash Cone." +The slope of the great cone of Teneriffe ranges from +28° to 38°; and below a level of 7000 feet the general +slope of the whole mountain down to the water's edge +varies from 10° to 12° from the horizontal. The great +cone is penetrated by numerous basaltic dykes.</p> + +<p>The Cape de Verde Islands, which contain beds of +limestone along with volcanic matter, possess in the +island of Fuego an active volcano, rising to a height +of 7000 feet above the surface of the ocean. The +central cone, like that of Teneriffe, rises from within +an outer crater, formed of basalt alternating with beds +of agglomerate, and traversed by numerous dykes of +lava. This has been broken down on one side like +that of Somma; and over its flanks are scattered +numerous cones of scoriæ, the most recent dating +from the years 1785 and 1799.<a name="FNanchor_3_35" id="FNanchor_3_35"></a><a href="#Footnote_3_35" class="fnanchor">[3]</a></p> + +<p><span class="pagenum"><a name="Page_35" id="Page_35">[Pg 35]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_5"> + <img src="images/figure5.jpg" alt="Summit of Teneriffe" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 5.</span>—View of the summit of the Peak of Teneriffe (12,225 feet) and of the secondary crater, or outer ring +of basaltic sheets which surrounds its base; seen from the east.—(After Leopold von Buch.) +</td></tr> +</table> +</div> + +<p>The volcanoes of Lancerote have a remarkably +linear arrangement from west to east across the +island. They are not yet extinct; for an eruption +in 1730 destroyed a large number of villages, and +covered with lava the most fertile tracts in the island, +which at the time of Leopold von Buch's visit lay +waste and destitute of herbage.<a name="FNanchor_4_36" id="FNanchor_4_36"></a><a href="#Footnote_4_36" class="fnanchor">[4]</a> In the island of +Palma there is one large central crater, the Caldera +de Palma, three leagues in diameter, the walls of +<span class="pagenum"><a name="Page_36" id="Page_36">[Pg 36]</a></span>which conform closely to the margin of the coast. +Von Buch calls this crater "une merveille de la +nature," for it distinguishes this isle from all the +others, and renders it one of the most interesting and +remarkable amongst the volcanic islands of the ocean. +The outer walls are formed of basaltic sheets, and +towards the south this great natural theatre is connected +with the ocean by a long straight valley, +called the "Barranco de los Dolores," along whose +sides the structure of the mountain is deeply laid +open to view. The outer flanks of the crater are +furrowed by a great number of smaller barrancos +radiating outward from the rim of the caldera. Von +Buch regards the barrancos as having been formed +during the upheaval of the island, according to his +theory of the formation of such mountains (the elevation-theory); +but unfortunately for his views, these +ravines widen outwards from the centre, or at least do +not become narrower in that direction, as would be +the case were the elevation-theory sound. The maps +which accompany Von Buch's work are remarkably +good, and were partly constructed by himself.</p> + +<p>(<i>c.</i>) <i>Volcanic Islands in the Atlantic south of the +Equator.</i>—The island of Ascension, formed entirely of +volcanic matter, rises from a depth of 2000 fathoms +in the very centre of the Atlantic. As described by +Darwin, the central and more elevated portions are +formed of trachytic matter, with obsidian and laminated +ash beds. Amongst these are found ejected +masses of unchanged granite, fragments of which +have been torn from the central pipe during +periods of activity, and would seem to indicate a +granitic floor, or at least an original floor upon which +more recent deposits may have been superimposed. +<span class="pagenum"><a name="Page_37" id="Page_37">[Pg 37]</a></span>In St. Helena we seem, according to Daubeny, to +have the mere wreck of one great crater, no one +stream of lava being traceable to its source, while +dykes of lava are scattered in profusion throughout +the whole substance of the basaltic masses which +compose the island. Tristan da Cunha, in the centre +of the South Atlantic, rises abruptly from a depth of +12,150 feet, at a distance of 1500 miles from any +land; and one of its summits reaches an elevation +of 7000 feet, being a truncated cone composed of +alternating strata of tuff and augitic lava, surrounding +a crater in which is a lake of pure water. The +volcano is extinct or dormant.</p> + +<p>Were the waters of the ocean to be drawn off, +these volcanic islands would appear like stupendous +conical mountains, far loftier, and with sides more +precipitous, than any to be found on our continental +lands, all of which rise from platforms of considerable +elevation. The enormous pressure of the water +on their sides enables these mid-oceanic islands to +stand with slopes varying from the perpendicular +to a smaller extent than if they were sub-aerial; +and it is on this account that we find them rising +with such extraordinary abruptness from the "vasty +deep."</p> + +<p>(<i>d.</i>) <i>Volcanic Islands of the Pacific.</i>—The volcanic +islands of this great ocean are scattered over a wide +tract on both sides of the equator. Those to the +north of this line include the Sandwich Islands, +the Mariana or Ladrone Islands, South Island, and +Bonin Sima; south of the equator, the Galapagos, +New Britain, Salomon, Santa Cruz, New Hebrides, +the Friendly and Society Isles. While the coral +reefs and islands of the Pacific may be recognised +<span class="pagenum"><a name="Page_38" id="Page_38">[Pg 38]</a></span>by their slight elevation above the surface of the +waters, those of volcanic origin and containing active +or extinct craters of eruption generally rise into +lofty elevations, so that the two kinds are called +the <i>Low</i> Islands and <i>High</i> Islands respectively. +Amongst the group are trachytic domes such as +the Mountain of Tobreonu in the Society Islands, +rising to a height probably not inferior to that of +Etna, with extremely steep sides, and holding a +lake on its summit.<a name="FNanchor_5_37" id="FNanchor_5_37"></a><a href="#Footnote_5_37" class="fnanchor">[5]</a> The linear arrangement of some +of the volcanic islands of the Pacific is illustrated +by those of the Tonga, or Friendly, Group, lying to +the north of New Zealand. They consist of three +divisions—(1) the volcanic; (2) those formed of +stratified volcanic tuff, sometimes entirely or partially +covered by coralline limestone; and (3) those which +are purely coralline. The first form a chain of lofty +cones and craters, lying in a E.N.E. and W.S.W. +direction, and rising from depths of over 1000 +fathoms. Mr. J. J. Lister, who has described the +physical characters of these islands, has shown very +clearly that they lie along a line—probably that of a +great fissure—stretching from the volcanic island of +Amargura on the north (lat. 18° S.), through Lette, +Metis, Kao (3030 feet), Tofua, Falcon, Honga Tonga, +and the Kermadec Group into the New Zealand +chain on the south. Some of these volcanoes are in +a state of intermittent activity, as in the case of +Tofua (lat. 20° 30' S.), Metis Island, and Amargura; +the others are dormant or extinct. The whole +group appears to have been elevated at a recent +period, as some of the beds of coral have been +raised 1272 feet and upward above the sea-level, +<span class="pagenum"><a name="Page_39" id="Page_39">[Pg 39]</a></span>as in the case of Eua Island.<a name="FNanchor_6_38" id="FNanchor_6_38"></a><a href="#Footnote_6_38" class="fnanchor">[6]</a> The greater number +of the Pacific volcanoes appear to be basaltic; +such as those of the Hawaiian Group, which have +been so fully described by Professor J. D. Dana.<a name="FNanchor_7_39" id="FNanchor_7_39"></a><a href="#Footnote_7_39" class="fnanchor">[7]</a> +Here fifteen volcanoes of the first class have been +in brilliant action; all of which, except three, are +now extinct, and these are in Hawaii the largest +and most eastern of the group. This island contains +five volcanic mountains, of which Kea, 13,805 +feet, is the highest; next to that, Loa, 13,675 feet; +after these, Hualalai, rising 8273 feet; Kilauea, +4158 feet; and Kohala, 5505 feet above the sea; this +last is largely buried beneath the lavas of Mauna Kea. +The group contains a double line of volcanoes, one +lying to the north and west of the other; and as the +highest of the Hawaiian Group rises from a depth in +the ocean of over 2000 fathoms, the total elevation +of this mountain from its base on the bed of the +ocean is not far from 26,000 feet, an elevation about +that of the Himalayas. Mauna Kea has long been +extinct, Hualalai has been dormant since 1801; but +Mauna Loa is terribly active, there having been +several eruptions, accompanied by earthquakes, within +recent years, the most memorable being those of +1852 and 1868. In the former case the lava rose +from the deep crater into "a lofty mountain," as +described by Mr. Coan,<a name="FNanchor_8_40" id="FNanchor_8_40"></a><a href="#Footnote_8_40" class="fnanchor">[8]</a> and then flowed away eastward +for a distance of twenty miles. The interior of +<span class="pagenum"><a name="Page_40" id="Page_40">[Pg 40]</a></span>the crater consists of a vast caldron, surrounded by a +precipice 200 to 400 feet in depth, with a circumference +of about fifteen miles, and containing within +it a second crater, bounded by a black ledge with a +steep wall of basalt—a crater within a crater; and from +the floor of the inner crater, formed of molten basalt, +in a seething and boiling state, arise a large number +of small cones and pyramids of lava, some emitting +columns of grey smoke, others brilliant flames and +streams of molten lava, presenting a wonderful spectacle, +the effect of which is heightened by the constant +roaring of the vast furnaces below.<a name="FNanchor_9_41" id="FNanchor_9_41"></a><a href="#Footnote_9_41" class="fnanchor">[9]</a></p> + +<div class="footnote"><p><a name="Footnote_1_33" id="Footnote_1_33"></a><a href="#FNanchor_1_33"><span class="label">[1]</span></a> <i>Principles of Geology</i>, 11th edition, vol. ii. p. 48.</p></div> + +<div class="footnote"><p><a name="Footnote_2_34" id="Footnote_2_34"></a><a href="#FNanchor_2_34"><span class="label">[2]</span></a> Smyth, <i>Report on the Teneriffe Astronomical Experiment of 1856</i>. +Humboldt makes the elevation 12,090 feet. A beautiful model of the +Peak was constructed by Mr. J. Nasmyth from Piazzi Smyth's plans, +of which photographs are given by the latter.</p></div> + +<div class="footnote"><p><a name="Footnote_3_35" id="Footnote_3_35"></a><a href="#FNanchor_3_35"><span class="label">[3]</span></a> Daubeny, <i>loc. cit.</i>, p. 460.</p></div> + +<div class="footnote"><p><a name="Footnote_4_36" id="Footnote_4_36"></a><a href="#FNanchor_4_36"><span class="label">[4]</span></a> <i>Iles Canaries</i>, p. 37.</p></div> + +<div class="footnote"><p><a name="Footnote_5_37" id="Footnote_5_37"></a><a href="#FNanchor_5_37"><span class="label">[5]</span></a> Daubeny, <i>loc. cit.</i>, p. 426.</p></div> + +<div class="footnote"><p><a name="Footnote_6_38" id="Footnote_6_38"></a><a href="#FNanchor_6_38"><span class="label">[6]</span></a> Lister, "Notes on the Geology of the Tonga Islands," <i>Quart. +Jour. Geol. Soc.</i>, No. 188, p. 590 (1891).</p></div> + +<div class="footnote"><p><a name="Footnote_7_39" id="Footnote_7_39"></a><a href="#FNanchor_7_39"><span class="label">[7]</span></a> Dana, <i>Characteristics of Volcanoes, with Contributions of Facts +and Principles from the Hawaiian Islands</i>. London, 1890.—Also, +<i>Geology of the American Exploring Expedition—Volcanoes of the +Sandwich Islands</i>.</p></div> + +<div class="footnote"><p><a name="Footnote_8_40" id="Footnote_8_40"></a><a href="#FNanchor_8_40"><span class="label">[8]</span></a> Coan, <i>Amer. Jour. of Science</i>, 1853.</p></div> + +<div class="footnote"><p><a name="Footnote_9_41" id="Footnote_9_41"></a><a href="#FNanchor_9_41"><span class="label">[9]</span></a> W. Ellis, the missionary, has given a vivid description of this +volcano in his <i>Tour of Hawaii</i>. London, 1826.—Plans of the crater +will be found in Professor Dana's work above quoted.</p></div> +<p><span class="pagenum"><a name="Page_41" id="Page_41">[Pg 41]</a></span></p> + + +<hr class="major" /> +<h1><a name="PART_II" id="PART_II"></a>PART II. +<br /><br /> +EUROPEAN VOLCANOES.</h1> + + + +<hr class="major" /> +<h2><a name="PART_II_CHAPTER_I" id="PART_II_CHAPTER_I"></a>CHAPTER I. +<br /><br /> +VESUVIUS.</h2> + + +<p>Having now dealt in a necessarily cursory manner +with volcanoes of distant parts of the globe, we may +proceed to the consideration of the group of active +volcanoes which still survive in Europe, as they possess +a special interest, not only from their proximity and +facility of access, at least to residents in Europe and +the British Isles, but from their historic incidents; +and in this respect Vesuvius, though not by any means +the largest of the group, stands the first, and demands +more special notice. The whole group rises from the +shores of the Mediterranean, and consists of Vesuvius, +Etna, Stromboli, one of the Lipari Islands, and +Vulcano, a mountain which has given the name to all +mountains of similar origin with itself.<a name="FNanchor_1_42" id="FNanchor_1_42"></a><a href="#Footnote_1_42" class="fnanchor">[1]</a> Along with +these are innumerable cones and craters of extinct or +dormant volcanoes, of which a large number have +been thrown out on the flanks of Etna.</p> + +<p>(<i>a.</i>) <i>Prehistoric Ideas regarding the Nature of this +Mountain.</i><span class="pagenum"><a name="Page_42" id="Page_42">[Pg 42]</a></span>—Down to the commencement of the +Christian era this mountain had given no ostensible +indication that it contained within itself a powerful +focus of volcanic energy. True, that some vague +tradition that the mountain once gave forth fire +hovered around its borders; and several ancient +writers, amongst them Diodorus Siculus and Strabo, +inferred from the appearances of the higher parts of +the mountain and the character of the rocks, which +were "cindery and as if eaten by fire," that the +country was once in a burning state, "being full of +fiery abysses, though now extinct from want of fuel." +Seneca (<span class="smcap">B.C.</span> 1 to <span class="smcap">A.D.</span> 64) had detected the true +character of Vesuvius, as "having been a channel for +the internal fire, but not its food;" nevertheless, at +this period the flanks of the mountain were covered +by fields and vineyards, while the summit, partially +enclosed with precipitous walls of the long extinct +volcano, Somma, was formed of slaggy and scoriaceous +material, with probably a covering of scrub. +Here it was that the gladiator Spartacus (<span class="smcap">B.C.</span> 72), +stung by the intolerable evils of the Roman +Government, retreated to the very summit of the +mountain with some trusty followers. Clodius the +Prætor, according to the narration of Plutarch, with +a party of three thousand men, was sent against them, +and besieged them in a mountain (meaning Vesuvius +or Somma) having but one narrow and difficult +passage, which Clodius kept guarded; all the rest +was encompassed with broken and slippery precipices, +but upon the top grew a great many wild vines; +the besieged cut down as many as they had need of, +and twisted them into ladders long enough to reach +from thence to the bottom, by which, without any +danger, all got down except one, who stayed behind +to throw them their arms, after which he saved +himself with the rest.<a name="FNanchor_2_43" id="FNanchor_2_43"></a><a href="#Footnote_2_43" class="fnanchor">[2]</a> "On the top" must (as +Professor Phillips observes) be interpreted the summit +of the exterior slope or crater edge, which would +appear from the narrative to have broken down on +one side, affording an entrance and mode of egress +by which Spartacus fell upon, and surprised, the +negligent Clodius Glabrus.</p> + +<p><span class="pagenum"><a name="Page_43" id="Page_43">[Pg 43]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_6"> + <img src="images/figure6.jpg" alt="Vesuvius in 1 A.D." /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 6.</span>—Probable aspect of Vesuvius as it appeared at the beginning of the Christian era; seen from the Bay of Naples. +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_44" id="Page_44">[Pg 44]</a></span></p><p>In fancied security, villas, temples, and cities had +been erected on the slopes of the mountain. Herculaneum, +Pompeii, and Stabiæ, the abodes of art, +luxury, and vice, had sprung up in happy ignorance +that they "stood on a volcano," and that their prosperity +was to have a sudden and disastrous close.<a name="FNanchor_3_44" id="FNanchor_3_44"></a><a href="#Footnote_3_44" class="fnanchor">[3]</a></p> + +<p>(<i>b.</i>) <i>Premonitory Earthquake Shocks.</i>—The first +monitions of the impending catastrophe occurred in +the 63rd year after Christ, when the whole Campagna +was shaken by an earthquake, which did much damage +to the towns and villas surrounding the mountain +even beyond Naples. This was followed by other +shocks; and in Pompeii the temple of Isis was so +much damaged as to require reconstruction, which +was undertaken and carried out by a citizen at his +own expense.<a name="FNanchor_4_45" id="FNanchor_4_45"></a><a href="#Footnote_4_45" class="fnanchor">[4]</a> These earthquake shakings continued +<span class="pagenum"><a name="Page_45" id="Page_45">[Pg 45]</a></span>for sixteen years. At length, on the night of August +24th, <span class="smcap">A.D. 79</span>, they became so violent that the whole +region seemed to reel and totter, and all things +appeared to be threatened with destruction. The next +day, about one in the afternoon, there was seen to +rise in the direction of Vesuvius a dense cloud, which, +after ascending from the summit of the mountain +into the air for a certain height in one narrow, vertical +trunk, spread itself out laterally in such a form that +the upper part might be compared to the cluster of +branches, and the lower to the stem of the pine which +forms so common a feature in the Italian landscape.<a name="FNanchor_5_46" id="FNanchor_5_46"></a><a href="#Footnote_5_46" class="fnanchor">[5]</a></p> + +<p>(<i>c.</i>) <i>Pliny's Letters to Tacitus.</i>—For an account of +what followed we are indebted to the admirable +letters of the younger Pliny, addressed to +the historian Tacitus, recounting the events which +caused, or accompanied, the death of his uncle, the +elder Pliny, who at the time of this first eruption of +Vesuvius was in command of the Roman fleet at the +entrance to the Bay of Naples. These letters, which +are models of style and of accurate description, are too +long to be inserted here; but he recounts how the +dense cloud which hung over the mountain spread +over the whole surrounding region, sometimes illuminated +by flashes of light more vivid than lightning; +how showers of cinders, stones, and ashes fell in +such quantity that his uncle had to flee from Stabiæ, +and that even at so great a distance as Misenum +they encumbered the surface of the ground; how the +ground heaved and the bed of the sea was upraised; +how the cloud descended on Misenum, and even the +island of Capreæ was concealed from view; and +<span class="pagenum"><a name="Page_46" id="Page_46">[Pg 46]</a></span>finally, how, urged by a friend who had arrived from +Spain, he, with filial affection, supported the steps of +his mother in flying from the city of destruction. +Such being the condition of the atmosphere and the +effects of the eruption at a point so distant as Cape +Misenum, some sixteen geographical miles from the +focus of eruption, it is only to be expected that +places not half the distance, such as Herculaneum, +Pompeii, and even Stabiæ, with many villages and +dwellings, should have shared a worse fate. The first +of these cities, situated on the coast of the Bay of +Naples, appears to have been overwhelmed by +volcanic mud; Pompeii was buried in ashes and +lapilli, and Stabiæ probably shared a similar fate.<a name="FNanchor_6_47" id="FNanchor_6_47"></a><a href="#Footnote_6_47" class="fnanchor">[6]</a></p> + +<p>(<i>d.</i>) <i>Appearance of the Mountain at the Commencement +of the Christian Era.</i>—At the time of the first +recorded eruption Vesuvius appears to have consisted +of only a single cone with a crater, now known as +<span class="pagenum"><a name="Page_47" id="Page_47">[Pg 47]</a></span>Monte di Somma, the central cone of eruption which +now rises from within this outer ruptured casing not +having been formed. (<a href="#FIGURE_6">Fig. 6</a>.) The first effect of the +eruption of the year 79 was to blow out the solidified +covering of slag and scoriæ forming the floor of the +caldron. Doubtless at the close of the eruption a cone +of fragmental matter and lava of some slight elevation +was built up, and, if so, was subsequently destroyed; +for, as we shall presently see by the testimony of the +Abate Guilio Cesare Braccini, who examined the +mountain not long before the great eruption of <span class="smcap">A.D. +1631</span>, there was no central cone to the mountain at +that time; and the mountain had assumed pretty +much the appearance it had at the time that Spartacus +took refuge within the walls of the great crater.</p> + +<p>(<i>e.</i>) <i>Destruction of Pompeii.</i>—Pompeii was overwhelmed +with dry ashes and lapilli. Sir W. Hamilton +found some of the stones to weigh eight pounds. At +the time of the author's visit, early in April 1872, the +excavations had laid open a section about ten feet +deep, chiefly composed of alternating layers of small +pumice stones (lapilli) and volcanic dust. It was +during the sinking of a well in 1713 upon the theatre +containing the statues of Hercules and Cleopatra that +the existence of the ancient city was accidentally +discovered.</p> + +<p>(<i>f.</i>) <i>More recent eruptions.</i>—Since the first recorded +eruption in <span class="smcap">A.D. 79</span> down to the present day, Vesuvius +has been the scene of numerous intermittent eruptions, +of which some have been recorded; but many, doubtless, +are forgotten.</p> + +<p>In <span class="smcap">A.D. 203</span>, during the reign of Severus, an eruption +of extraordinary violence took place, which is +related by Dion Cassius, from whose narrative we +<span class="pagenum"><a name="Page_48" id="Page_48">[Pg 48]</a></span>may gather that at this time there was only one +large crater, and that the central cone of Vesuvius +had not as yet been upraised. In <span class="smcap">A.D. 472</span> an eruption +occurred of such magnitude as to cover all Europe +with fine dust, and spread alarm even at Constantinople.</p> + +<p>(<i>g.</i>) <i>Eruption of 1631.</i>—In December 1631 occurred +the great convulsion whose memorials are written widely +on the western face of Vesuvius in ruined villages. This +eruption left layers of ashes over hundreds of miles of +country, or heaps of mud swept down by hot water +floods from the crater; the crater itself having been +dissipated in the convulsion. Braccini, who examined +the mountain not long before this eruption, found +apparently no cone (or mount) like that of the modern +Vesuvius. He states that the crater was five miles in +circumference, about a thousand paces deep (or in +sloping descent), and its sides covered with forest +trees and brushwood, while at the bottom there was a +plain on which cattle grazed.<a name="FNanchor_7_48" id="FNanchor_7_48"></a><a href="#Footnote_7_48" class="fnanchor">[7]</a> It would seem that +the mountain had at this time enjoyed a long interval +of rest, and that it had reverted to very much the +same state in which it was at the period of the first +eruption, when the flanks were peopled by inhabitants +living in fancied security. But six months of violent +earthquakes, which grew more violent towards the close +of 1631, heralded the eruption which took place in +December, accompanied by terrific noises from within +the interior of the mountain. The inhabitants of the +coast were thus warned of the approaching danger, +and had several days to arrange for their safety; but +in the end, a great part of Torre del Greco was +destroyed, and a like fate overtook Resina and +<span class="pagenum"><a name="Page_49" id="Page_49">[Pg 49]</a></span>Granatello, with a loss of life reported at 18,000 +persons. During the eruption clouds condensed into +tempests of rain, and hot water from the mountain, +forming deluges of mud, swept down the sides, and +reached even to Nola and the Apennines. Nor was +the sea unmoved. It retired during the violent earthquakes, +and then returned full thirty paces beyond +its former limits.</p> + +<p>Not indeed until near the close of the seventeenth +century is there any evidence that the central cone of +Vesuvius was in existence; but in October 1685 an +eruption occurred which is recorded by Sorrentino, +during which was erected "a new mountain within, +and higher than the old one, and visible from Naples," +a statement evidently referable to the existing cone—so +that it is little more than two centuries since this +famous volcanic mountain assumed its present form.</p> + +<p>(<i>h.</i>) <i>Eruptions between the years 1500 and 1800.</i>—Since +<span class="smcap">A.D. 1500</span> there have been fifty-six recorded +eruptions of Vesuvius; one of these in 1767 was of +terrific violence and destructiveness, and is represented +by Sir William Hamilton in views taken both before +and during the eruption. A pen-and-ink drawing of +the appearance of the crater before the eruption is here +reproduced from Hamilton's picture, from which it +will be seen that the central crater contained within +itself a second crater-cone, from whence steam, lava, +and stones were being erupted (<a href="#FIGURE_7">Fig. 7</a>). Thus it will +be seen that Vesuvius at this epoch consisted of three +crater-cones within each other. The first, Monte di +Somma; the second, the cone of Vesuvius; and the +third, the little crater-cone within the second. During +this eruption, vast lava-sheets invaded the fields and +vineyards on the flanks of the mountain. A vivid +<span class="pagenum"><a name="Page_50" id="Page_50">[Pg 50]</a></span>account of this eruption, as witnessed by Padre Torre, +is given by Professor Phillips.<a name="FNanchor_8_49" id="FNanchor_8_49"></a><a href="#Footnote_8_49" class="fnanchor">[8]</a> We shall pass over +others without further reference until we come down +to our own times, in which Vesuvius has resumed its +old character, and in one grand exhibition of volcanic +energy, which took place in 1872, has evinced to the +world that it still contains within its deep-seated +laboratory all the elements of destructive force which +it exhibited at the commencement of our era.</p> + +<div class="figcenter"> +<a name="FIGURE_7"> + <img src="images/figure7.jpg" alt="Vesuvius before 1767" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 7.</span>—View of the crater of Vesuvius before the eruption of 1767, +showing an interior crater-cone rising from the centre of the exterior +crater.—(After Sir W. Hamilton.) +</td></tr> +</table> +</div> + +<p>(<i>i.</i>) <i>Structure of the Neapolitan Campagna.</i>—But before +giving a description of this terrific outburst of volcanic +energy, it may be desirable to give some account +of the physical position and structure of this mountain, +by which the phenomena of the eruption will be better +<span class="pagenum"><a name="Page_51" id="Page_51">[Pg 51]</a></span>understood. Vesuvius and the Neapolitan Campagna +are formed of volcanic materials bounded on the west +by the Gulf of Naples, and on the east and south by +ranges of Jurassic limestone, a prolongation of the +Apennines, which send out a spur bounding the bay on +the south, and forming the promontory of Sorrento. +The little island of Capri is also formed of limestone, +and is dissevered from the promontory by a narrow +channel. The northern side of the bay is, however, +formed of volcanic materials; it includes the +Phlegræan Fields (Campi Phlegræi), and terminates +in the promontory of Miseno. Lying in the same +direction are the islands of Procida and Ischia, also +volcanic. Hence it will be seen that the two horns +of the bay are formed of entirely different materials, +that of Miseno on the north being volcanic, that of +Sorrento on the south being composed of Jurassic +limestone, of an age vastly more ancient than the +volcanic rocks on the opposite shore. (<a href="#FIGURE_8">Map, p. 52</a>.)</p> + +<p>The general composition of the Neapolitan +Campagna, from which the mountain rises, has +been revealed by means of the Artesian well sunk to +a depth of about 500 metres (1640 feet) at the Royal +Palace of Naples, and may be generalised as +follows:—</p> +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" style="width:90%;" summary=""> +<tr> +<td align="left" valign="middle" style="width:40%;">(1) From surface to depth of 715 feet</td> +<td align="left"><span style="font-size:200%;">{</span></td> +<td align="left">Recent beds of volcanic tuff with marine shells, and containing fragments of trachytic lava, etc. (<i>Volcanic Beds</i>).</td> +</tr> +<tr> +<td align="left" valign="middle">(2) From 715 to 1420</td> +<td align="left"><span style="font-size:200%;">{</span></td> +<td align="left">Bituminous sands and marls with marine shells of recent species(?) (<i>Pre-Volcanic Beds</i>).</td> +</tr> +<tr> +<td align="left" valign="middle">(3) From 1420 to 1574</td> +<td align="left"><span style="font-size:200%;">{</span></td> +<td align="left"><span class="smcap">Eocene Beds.</span> Micaceous sandstone and marl (<i>Macigno</i>).</td> +</tr> +<tr> +<td align="left" valign="middle">(4) From 1574 to bottom</td> +<td align="left"><span style="font-size:200%;">{</span></td> +<td align="left"><span class="smcap">Jurassic Beds.</span> Apennine Limestone.</td> +</tr> +</table> +</div> +<p><span class="pagenum"><a name="Page_52" id="Page_52">[Pg 52]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_8"> + <img src="images/figure8.jpg" alt="Bay of Naples" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 8.</span>—Map of the district bordering the Bay of Naples, with the +islands of Capri, Ischia, and Procida. +</td></tr> +</table> +</div> + +<p>From the above section, for which we are indebted to +Mr. Johnston-Lavis, the most recent writer on Vesuvius, +it would appear that the first volcanic explosions by +which the mountain was ultimately to be built up +took place after the deposition of the sands and +marls (No. 2), while the whole Campagna was submerged +under the waters of the Mediterranean. By +the accumulation of the stratified tuff (No. 1), the sea-bed +was gradually filled up during a period of volcanic +activity, and afterwards elevated into dry land.<a name="FNanchor_9_50" id="FNanchor_9_50"></a><a href="#Footnote_9_50" class="fnanchor">[9]</a></p> + +<p><span class="pagenum"><a name="Page_53" id="Page_53">[Pg 53]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_9"> + <img src="images/figure9.jpg" alt="Vesuvius eruption of 1872" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 9.</span>—View of Vesuvius from the Harbour of Naples at the commencement of the eruption of 1872.—(From +a sketch by the author.) +</td></tr> +</table> +</div> + +<p>(<i>j.</i>) <i>Present Form and Structure of Vesuvius and +Somma.</i>—The outer cone of Vesuvius, or Monte di +Somma, rises from a circular platform by a moderately +gentle ascent, and along the north and east terminates +<span class="pagenum"><a name="Page_54" id="Page_54">[Pg 54]</a></span>in a craggy crest, with a precipitous cliff descending +into the Atria del Cavallo, forming the wall of the +ancient crater throughout half its circumference; this +wall is formed of scoriæ, ashes, and lapilli, and is +traversed by numerous dykes of lava. Along the +west and south this old crater has been broken +down; but near the centre there remains a round-backed +ridge of similar materials, once doubtless a +part of the original crater of Somma, rising above +the slopes of lava on either hand. On this has been +erected the Royal Observatory, under the superintendence +of Professor Luigi Palmieri, where continuous +observations are being made, by means of delicate +seismometers, of the earth-tremors which precede or +accompany eruptions; for it is only justice to say that +Vesuvius gives fair warning of impending mischief, +and the instruments are quick to notify any premonitory +symptoms of a coming catastrophe. The elevation +of the Observatory is 2080 feet above the sea.</p> + +<p>On either side of the Observatory ridge are wide +channels filled to a certain height with lavas of the +nineteenth and preceding centuries, the most recent +presenting an aspect which can only be compared to +a confused multitude of black serpents and pachyderms +writhing and interlocked in some frightful +death-struggle. Some of this lava, ten years old, as +we cross its rugged and black surface presents gaping +fissures, showing the mass to be red-hot a few feet +from the surface, so slow is the process of cooling. +These lava-streams—some of them reaching to the +sea-coast—have issued forth from the Atria at +successive periods of eruption.</p> + +<p>From the midst of the Atria rises the central +cone, formed of cinders, scoriæ, and lava-streams, and +<span class="pagenum"><a name="Page_55" id="Page_55">[Pg 55]</a></span>fissured along lines radiating from the axis. This +cone is very steep, the angle being about 40°-45° +from the horizontal, and is formed of loose cindery +matter which gives way at every step, and is rather +difficult to climb. But on reaching the summit we +look down into the crater, displaying a scene of ever-varying +characters, rather oval in form, and about +1100 yards in diameter. From the map of Professor +Guiscardi, published in 1855, there are seen two +minor craters within the central one, formed in 1850, +and an outflow of lava from the N.W. down the +cone. At the time of the author's visit the crater +was giving indications, by the great quantity of sulphurous +gas and vapour rising from its surface, and +small jets of molten lava beginning to flow down +the outer side, of the grand outburst of internal +forces which was presently to follow.</p> + +<p>(<i>k.</i>) <i>Eruption of 1872.</i>—The grand eruption of +1872, of which a detailed account is given by Professor +Palmieri,<a name="FNanchor_10_51" id="FNanchor_10_51"></a><a href="#Footnote_10_51" class="fnanchor">[10]</a> commenced with a slight discharge of incandescent +projectiles from the crater; and on the +13th January an aperture appeared on the upper edge +of the cone from which at first a little lava issued +forth, followed by the uprising of a cone which +threw out projectiles accompanied by smoke, whilst +the central crater continued to detonate more loudly +and frequently. This little cone ultimately increased +in size, until in April it filled the whole crater and +rose four or five metres above the brim. At this +time abundant lavas poured down from the base of +the cone into the Atria del Cavallo, thence turned +into the Fossa della Vetraria in the direction of the +<span class="pagenum"><a name="Page_56" id="Page_56">[Pg 56]</a></span>Observatory and towards the Crocella, where they +accumulated to such an extent as to cover the hillside +for a distance of about 300 metres; then turning +below the Canteroni, formed a hillock without spreading +much farther.</p> + +<p>In October another small crater was formed by the +falling in of the lava, which after a few days gave vent +to smoke and several jets of lava; and towards the +end of October the detonations increased, the smoke +from the central crater issued forth more densely +mixed with ashes, and the seismographical apparatus +was much disturbed. On the 3rd and 4th November +copious and splendid lava-streams coursed down the +principal cone on its western side, but were soon +exhausted; and in the beginning of 1872 the little +cone, regaining vigour, began to discharge lava from +the summit instead of the base as heretofore.</p> + +<p>In the month of March 1873, with the full moon, +the cone opened on the north-west side—the cleavage +being indicated by a line of fumaroles—and lava +issued from the base and poured down into the Atria +as far as the precipices of Monte di Somma. On the +23rd April (another full moon) the activity of the +craters increased, and on the evening of the 24th +splendid lava-streams descended the cone in various +directions, attracting on the same night the visits of +a great many strangers. A lamentable event followed +on the 26th. A party of visitors, accompanied by +inexperienced guides, and contrary to the advice of +Professor Palmieri, insisted on ascending to the place +from which the lava issued. At half-past three on the +morning of the 26th they were in the Atria del Cavallo, +when the Vesuvian cone was rent in a north-west +direction and a copious torrent of lava issued forth. +<span class="pagenum"><a name="Page_57" id="Page_57">[Pg 57]</a></span>Two large craters formed at the summit of the +mountain, discharging incandescent projectiles and +ashes. A cloud of smoke enveloped the unhappy +visitors, who were under a hail-storm of burning +projectiles. Eight were buried beneath it, or in +the lava, while eleven were grievously injured.<a name="FNanchor_11_52" id="FNanchor_11_52"></a><a href="#Footnote_11_52" class="fnanchor">[11]</a> +The lava-stream, flowing over that of 1871 in the +Atria, divided into two branches, the smaller one +flowing towards Resina, but stopping before reaching +the town; the larger precipitated itself into the Fossa +della Vetraria, occupying the whole width of 800 +metres, and traversing the entire length of 1300 +metres in three hours. It dashed into the Fossa di +Farone, and reached the villages of Massa and St. +Sebastiano, covering a portion of the houses, and, continuing +its course through an artificial foss, or trench, +invaded cultivated ground and several villages. If it +had not greatly slackened after midnight, from failure +of supply at its source, it would have reached Naples +by Ponticelli and flowed into the sea. The eruption +towards the end of April had reached its height. The +Observatory ridge was bounded on either side by two +fiery streams, which rendered the heat intolerable. +Simultaneously with the opening of the great fissure +two large craters opened at the summit, discharging +with a dreadful noise an immense cloud of smoke and +ashes, with bombs which rose to a height of 1300 +metres above the brim of the volcano.<a name="FNanchor_12_53" id="FNanchor_12_53"></a><a href="#Footnote_12_53" class="fnanchor">[12]</a> The torrents +of fire which threatened Resina, Bosco, and Torre +Annunziata, and which devastated the fertile country +<span class="pagenum"><a name="Page_58" id="Page_58">[Pg 58]</a></span>of Novelle, Massa, St. Sebastiano, and Cerole, and +two partially buried cities, the continual thunderings +and growling of the craters, caused such terror, that +numbers abandoned their dwellings, flying for refuge +into Naples, while many Neapolitans went to Rome +or other places. Fortunately, the paroxysm had now +passed, the lava-streams stopped in their course, and +the great torrent which passed the shoulders of the +Observatory through the Fossa della Vetraria lowered +the level of its surface below that of its sides, which +appeared like two parallel ramparts above it. Had +these streams continued to flow on the 27th of April +as they had done on the previous night, they would +have reached the sea, bringing destruction to the very +walls of Naples. During this eruption Torre del +Greco was upraised to the extent of two metres, and +nearly all the houses were knocked down.</p> + +<p>The igneous period of eruption having terminated, +the ashes, lapilli, and projectiles became more +abundant, accompanied by thunder and lightning. +On the 28th they darkened the air, and the terrific +noise of the mountain continuing or increasing, the +terror at Resina, Portici, and Naples became universal. +It seemed as though the tragic calamities +of the eruption of <span class="smcap">A.D.</span> 79 were about to be repeated. +But gradually the force of the explosions decreased, +and the noise from the crater became discontinuous, +so that on the 30th the detonations were very few, +and by the 1st May the eruption was completely +over.</p> + +<p>Such is a condensed account of one of the most +formidable eruptions of our era. In the frontispiece +of this volume a representation, taken (by permission) +from a photograph by Negretti & Zambra, is given, +<span class="pagenum"><a name="Page_59" id="Page_59">[Pg 59]</a></span>showing the appearance of Vesuvius during the final +stage of the eruption, when prodigious masses of +smoke, steam, and illuminated gas issued forth from +the summit and overspread the whole country around +with a canopy which the light of the sun could +scarcely penetrate.</p> + +<p>It will be noticed in the above account that, concurrently +with the full moon, there were two distinct +and special outbreaks of activity; one occurring in +March, the other in the month following. That the +conditions of lunar and solar attraction should have +a marked effect on a part of the earth's crust, while +under the tension of eruptive forces, is only what +might be expected. At full moon the earth is +between the sun and the moon, and at new moon +the moon is between the sun and the earth; +under these conditions (the two bodies acting in +concert) we have spring tides in the ocean, and a +maximum of attraction on the mass of the earth. +Hence the crust, which at the time referred to was +under tremendous strain, only required the addition +of that caused by the lunar and solar attractions to +produce rupture in both cases, giving rise to increased +activity, and the extrusion of lava and volatile matter. +It may, in general, be safely affirmed that low barometric +pressure on the one hand, and the occurrence +of the syzygies (when the attractions of the sun and +moon are in the same line) on the other, have had +great influence in determining the crises of eruptions +of volcanic mountains when in a state of unrest.</p> + +<p><i>Contrast between the Northern and Southern Slopes.</i>—Before +leaving Vesuvius it may be observed that +throughout all the eruptions of modern times the +northern side of the mountain, that is the old crater +<span class="pagenum"><a name="Page_60" id="Page_60">[Pg 60]</a></span>and flank of Somma, has been secure from the +lava-flows, and has enjoyed an immunity which does +not belong to the southern and western side. If we +look at a map of the mountain showing the direction +of the streams during the last three centuries,<a name="FNanchor_13_54" id="FNanchor_13_54"></a><a href="#Footnote_13_54" class="fnanchor">[13]</a> we +observe that all the streams of that period flowed +down on the side overlooking the Bay of Naples; on +the opposite side the wall of Monte di Somma +presents an unbroken front to the lava-streams. From +this it may be inferred that one side, the west, is +weaker than the other; and consequently, when the +lava and vapours are being forced upwards, under +enormous pressure from beneath, the western side +gives way under the strain, as in the case of the +fissure of 1872, and the lava and vapours find means +of escape. From what has happened in the past it +is clear that no place on the western side of the +mountain is entirely safe from devastation by floods +of lava; while the prevalent winds tend to carry the +ashes and lapilli, which are hurled into the air, in the +same westerly direction.</p> + +<div class="footnote"><p><a name="Footnote_1_42" id="Footnote_1_42"></a><a href="#FNanchor_1_42"><span class="label">[1]</span></a> For an excellent view of this remarkable volcanic group see Judd's +<i>Volcanoes</i>, 4th edition, p. 43.</p></div> + +<div class="footnote"><p><a name="Footnote_2_43" id="Footnote_2_43"></a><a href="#FNanchor_2_43"><span class="label">[2]</span></a> Plutarch, <i>Life of Cassius</i>; <i>ed. Reiske</i>, vol. iii. p. 240.</p></div> + +<div class="footnote"><p><a name="Footnote_3_44" id="Footnote_3_44"></a><a href="#FNanchor_3_44"><span class="label">[3]</span></a> Strabo gives the following account of the appearance and condition +of Vesuvius in his day:—"Supra hæc loca situs est Vesuvius mons, +agris cinctus optimis; dempto vertice, qui magna sui parte planus, +totus sterilis est, adspectu sinereus, cavernasque ostendens fistularum +plenas et lapidum colore fuliginoso, utpote ab igni exesorum. Ut conjectarum +facere possis, ista loca quondam arsisse et crateras ignis +habuisse, deinde materia deficiente restricta fuisse."—<i>Rer. Geog.</i>, lib. v.</p></div> + +<div class="footnote"><p><a name="Footnote_4_45" id="Footnote_4_45"></a><a href="#FNanchor_4_45"><span class="label">[4]</span></a> A tablet over the entrance records this act of pious liberality, and +is given by Phillips, <i>loc. cit.</i>, p. 12.</p></div> + +<div class="footnote"><p><a name="Footnote_5_46" id="Footnote_5_46"></a><a href="#FNanchor_5_46"><span class="label">[5]</span></a> The stone pine, <i>Pinus pinea</i>, which Turner knew how to use with +so much effect in his Italian landscapes.</p></div> + +<div class="footnote"><p><a name="Footnote_6_47" id="Footnote_6_47"></a><a href="#FNanchor_6_47"><span class="label">[6]</span></a> Bulwer Lytton's <i>Last Days of Pompeii</i> presents to the reader a +graphic picture of the terrible event here referred to:—"The eyes of the +crowd followed the gesture of the Egyptian, and beheld with ineffable +dismay a vast vapour shooting from the summit of Vesuvius, in the +form of a gigantic pine tree; the trunk—blackness, the branches—fire! +A fire that shifted and wavered in its hues with every moment—now +fiercely luminous, now of a dull and dying red that again blazed +terrifically forth with intolerable glare!... Then there arose on high +the shrieks of women; the men stared at each other, but were speechless. +At that moment they felt the earth shake beneath their feet; +the walls of the theatre trembled; and beyond, in the distance, they +heard the crash of falling roofs; an instant more and the mountain-cloud +seemed to roll towards them, dark and rapid; at the same time +it cast forth from its bosom a shower of ashes mixed with vast fragments +of burning stone. Over the crushing vines—over the desolate streets—over +the amphitheatre itself—far and wide, with many a mighty +splash in the agitated sea, fell that awful shower." A visit to the disinterred +city will probably produce on the mind a still more lasting and +vivid impression of the swift destruction which overtook this city.</p></div> + +<div class="footnote"><p><a name="Footnote_7_48" id="Footnote_7_48"></a><a href="#FNanchor_7_48"><span class="label">[7]</span></a> Quoted by Phillips, <i>loc. cit.</i>, p. 45.</p></div> + +<div class="footnote"><p><a name="Footnote_8_49" id="Footnote_8_49"></a><a href="#FNanchor_8_49"><span class="label">[8]</span></a> <i>Vesuvius</i>, p. 72 <i>et seq.</i></p></div> + +<div class="footnote"><p><a name="Footnote_9_50" id="Footnote_9_50"></a><a href="#FNanchor_9_50"><span class="label">[9]</span></a> Johnston-Lavis, "On the Geology of Monti Somma and Vesuvius," +<i>Quart. Jour. Geol. Soc.</i>, vol. 40 (1884).</p></div> + +<div class="footnote"><p><a name="Footnote_10_51" id="Footnote_10_51"></a><a href="#FNanchor_10_51"><span class="label">[10]</span></a> Palmieri, <i>Eruption of Vesuvius in 1872</i>, with notes, etc., by +Robert Mallet, F.R.S. London, 1873.</p></div> + +<div class="footnote"><p><a name="Footnote_11_52" id="Footnote_11_52"></a><a href="#FNanchor_11_52"><span class="label">[11]</span></a> Those who lost their lives were medical students, and an Assistant +Professor in the University, Antonio Giannone by name.</p></div> + +<div class="footnote"><p><a name="Footnote_12_53" id="Footnote_12_53"></a><a href="#FNanchor_12_53"><span class="label">[12]</span></a> Involving, as Mr. Mallet calculates, an initial velocity of projection +of above 600 feet per second.</p></div> + +<div class="footnote"><p><a name="Footnote_13_54" id="Footnote_13_54"></a><a href="#FNanchor_13_54"><span class="label">[13]</span></a> Such as that given by Professor Phillips in his <i>Vesuvius</i>.</p></div> +<p><span class="pagenum"><a name="Page_61" id="Page_61">[Pg 61]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_II_CHAPTER_II" id="PART_II_CHAPTER_II"></a>CHAPTER II. +<br /><br /> +ETNA.</h2> + + +<p>(<i>a.</i>) <i>Structure of the Mountain.</i>—Etna, unlike Vesuvius, +has ever been a burning mountain; hence it +was well known as such to classic writers before the +Christian era. The structure and features of this +magnificent mountain have been abundantly illustrated +by Elie de Beaumont,<a name="FNanchor_1_55" id="FNanchor_1_55"></a><a href="#Footnote_1_55" class="fnanchor">[1]</a> Daubeny,<a name="FNanchor_2_56" id="FNanchor_2_56"></a><a href="#Footnote_2_56" class="fnanchor">[2]</a> Baron von +Waltershausen,<a name="FNanchor_3_57" id="FNanchor_3_57"></a><a href="#Footnote_3_57" class="fnanchor">[3]</a> and Lyell,<a name="FNanchor_4_58" id="FNanchor_4_58"></a><a href="#Footnote_4_58" class="fnanchor">[4]</a> of whose writings I shall +freely avail myself in the following account, not +having had the advantage of a personal examination +of this region.</p> + +<p><i>Structure of Etna.</i>—So large is Etna that it would +enclose within its ample skirts several cones of the size +of Vesuvius. It rises to a height of nearly 11,000 +feet above the waters of the Mediterranean,<a name="FNanchor_5_59" id="FNanchor_5_59"></a><a href="#Footnote_5_59" class="fnanchor">[5]</a> and is +planted on a floor consisting of stratified marine +volcanic matter, with clays, sands, and limestones of +newer Pliocene age. Its base is nearly circular, and +has a circumference of 87 English miles. In ascending +<span class="pagenum"><a name="Page_62" id="Page_62">[Pg 62]</a></span>its flanks we pass successively over three well-defined +physical zones: the lowest, or fertile zone, +comprising the tract around the skirts of the mountain +up to a level of about 2500 feet, being well cultivated +and covered by dwellings surrounded by olive groves, +fields, vineyards, and fruit-trees; the second, or forest +zone, extending to a level of about 6270 feet, clothed +with chestnut, oak, beech, and cork trees, giving place +to pines; and the third, extending to the summit and +called "the desert region," a waste of black lava and +scoriæ with mighty crags and precipices, terminating +in a snow-clad tableland, from which rises the central +cone, 1100 feet high, emitting continually steam and +sulphurous vapours, and in the course of almost every +century sending forth streams of molten lava.</p> + +<p>The forest zone is remarkable for the great number +of minor craters which rise up from the midst of +the foliage, and are themselves clothed with trees. +Sartorius von Waltershausen has laid down on his +map of Etna about 200 of these cones and craters, +some of which, like those of Auvergne, have been +broken down on one side. Many of these volcanoes of +second or third magnitude lie outside the forest zone, +both above and below it; such as the double hill of +Monti Rossi, near Nicolosi, formed in 1659, which +is 450 feet in height, and two miles in circumference +at its base. Sir C. Lyell observes that +these minor crater-cones present us with one of +the most delightful and characteristic scenes in +Europe. They occur of every variety of height and +size, and are arranged in picturesque groups. However +uniform they may appear when seen from +the sea or the plains below, nothing can be more +diversified than their shape when we look from above +<span class="pagenum"><a name="Page_63" id="Page_63">[Pg 63]</a></span>into their ruptured craters. The cones situated in +the higher parts of the forest zone are chiefly clothed +with lofty pines; while those at a lower elevation are +adorned with chestnuts, oaks, and beech trees. These +cones have from time to time been buried amidst +fresh lava-streams descending from the great crater, +and thus often become obliterated.</p> + +<div class="figcenter"> +<a name="FIGURE_10"> + <img src="images/figure10.jpg" alt="Section through Etna" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 10.</span>—Ideal Section through Etna. (After Lyell.)—A. Axis of +present cone of eruption; B. Axis of extinct cone of eruption; <i>a.</i> Older +lavas, chiefly trachytic; <i>b.</i> Newer lavas, erupted (with <i>a</i>) before origin +of the Val del Bove; <i>c.</i> Scoria and lava of recent age; T. Tertiary +strata forming the foundation to the volcanic rocks. The position of +the Val del Bove before its formation is shown by the lightly-shaded +portion above B. +</td></tr> +</table> +</div> + +<p>(<i>b.</i>) <i>Val del Bove.</i>—The most wonderful feature of +Mount Etna is the celebrated Val del Bove (Valle del +Bue), of which S. von Waltershausen has furnished a +very beautiful plate<a name="FNanchor_6_60" id="FNanchor_6_60"></a><a href="#Footnote_6_60" class="fnanchor">[6]</a>—a vast amphitheatre hewn +out of the eastern flank of the mountain, just below +the snow-mantled platform. It is a physical feature +somewhat after the fashion of Monte Somma in +Vesuvius, but exceeds it in magnitude as Etna +exceeds Vesuvius. The Val del Bove is about five +miles in diameter, bounded throughout three-fourths +of its circumference by precipitous walls of ashes, +scoriæ, and lava, traversed by innumerable dykes, and +rising inwards to a height of between 3000 and 4000 +<span class="pagenum"><a name="Page_64" id="Page_64">[Pg 64]</a></span>feet. Towards the east the cliffs gradually fall to a +height of about 500 feet, and at this side the vast +chasm opens out upon the slope of the mountain. At +the head of the Val del Bove rises the platform, +surmounted by the great cone and crater. It will +thus be seen that by means of this hollow we have +access almost to the very heart of the mountain.</p> + +<p>What is very remarkable about the structure of this +valley is that the beds exhibit "the <i>quâ-quâ</i> versal +dip"—in other words, they dip away on all sides from +the centre—which has led to the conclusion that in +the centre is a focus of eruption which had become +closed up antecedently to the formation of the valley +itself. Lyell has explained this point very clearly by +showing that this focus had ceased to eject matter at +some distant period, and that the existing crater at +the summit of the mountain had poured out its lavas +over those of the extinct orifice. This was prior to +the formation of the Val del Bove itself; and the +question remains for consideration how this vast +natural amphitheatre came to be hollowed out; for +its structure shows unquestionably that it owes its +form to some process of excavation.</p> + +<p>In the first place, it is certainly not the work of +running water, as in the case of the cañons of +Colorado; the porous matter of which the mountain +is formed is quite incapable of originating and supporting +a stream of sufficient volume to excavate and +carry away such enormous masses of matter within +the period required for the purpose. We must therefore +have recourse to some other agency. Numerous +illustrations are to be found of the explosive action of +volcanoes in blowing off either the summits of mountains, +or portions of their sides. For example, there +<span class="pagenum"><a name="Page_65" id="Page_65">[Pg 65]</a></span>is reason for believing that the first result of the +renewed energy of Vesuvius was to blow into the air +the upper surface of the mountain. Again, so late as +1822, during a violent earthquake in Java, a country +which has been repeatedly devastated by earthquakes +and volcanic eruptions, the mountain of Galongoon, +which was covered by a dense forest, and situated in +a fertile and thickly-peopled region, and had never +within the period of tradition been in activity, was +thus ruptured by internal forces. In the month of +July 1822, after a terrible earthquake, an explosion +was heard, and immense columns of boiling water, +mixed with mud and stones, were projected from the +mountain like a water-spout, and in falling filled up the +valleys, and covered the country with a thick deposit +for many miles, burying villages and their inhabitants. +During a subsequent eruption great blocks of basalt +were thrown to a distance of seven miles; the result +of all being that an enormous semicircular gulf was +formed between the summit and the plain, bounded +by steep cliffs, and bearing considerable resemblance +to the Val del Bove. Other examples of the power +of volcanic explosions might be cited; but the above +are sufficient to show that great hollows may thus be +formed either on the summits or flanks of volcanic +mountains. Chasms may also be formed by the +falling in of the solidified crust, owing to the extrusion +of molten matter from some neighbouring vent of +eruption; and it is conceivable that by one or other +of these processes the vast chasm of the Val del Bove +on the flanks of Etna may have been produced.</p> + +<p>(<i>c.</i>) <i>The Physical History of Etna.</i>—The physical +history of Etna seems to be somewhat as follows:—</p> + +<p><i>First Stage.</i>—Somewhere towards the close of the +<span class="pagenum"><a name="Page_66" id="Page_66">[Pg 66]</a></span>Tertiary period—perhaps early Pliocene or late +Miocene—a vent of eruption opened on the floor of +the Mediterranean Sea, from which sheets of lava +were poured forth, and ashes mingled with clays and +sands, brought down from the neighbouring lands, +were strewn over the sea-bed. During a pause in +volcanic activity, beds of limestone with marine shells +were deposited.</p> + +<p><i>Second Stage.</i>—This sea-bed was gradually upraised +into the air, while fresh sheets of lava and other <i>ejecta</i> +were accumulated round the vents of eruption, of +which there were two principal ones—the older under +the present Val del Bove, the newer under the summit +of the principal cone. Thus was the mountain gradually +piled up.</p> + +<p><i>Third Stage.</i>—The vent under the Val del Bove +ceased to extrude more matter, and became extinct. +Meanwhile the second vent continued active, and, +piling up more and more matter round the central +crater, surmounted the former vent, and covered its +<i>ejecta</i> with newer sheets of lava, ashes, and lapilli, +while numerous smaller vents, scattered all over the +sides of the mountain, gave rise to smaller cones and +craters.</p> + +<p><i>Fourth Stage.</i>—This stage is signalised by the +formation of the Val del Bove through some grand +explosion, or series of explosions, by which this vast +chasm was opened in the side of the mountain, as +already explained.</p> + +<p><i>Fifth Stage.</i>—This represents the present condition +of the mountain, whose height above the sea is due, +not only to accumulation of volcanic materials round +the central cone, but to elevation of the whole island, +as evinced by numerous raised beaches of gravel and +<span class="pagenum"><a name="Page_67" id="Page_67">[Pg 67]</a></span>sand, containing shells and other forms of marine +species now living in the waters of the Mediterranean.<a name="FNanchor_7_61" id="FNanchor_7_61"></a><a href="#Footnote_7_61" class="fnanchor">[7]</a> +Since then the condition and form of the +mountain has remained very much the same, varied +only by the results of occasional eruptions.</p> + +<p>(<i>d.</i>) <i>Dissimilarity in the Constitution of the Lavas +of Etna and Vesuvius.</i>—Before leaving the subject we +have been considering, it is necessary that I should +mention one remarkable fact connected with the origin +of the lavas of Etna and Vesuvius respectively; I refer +to their essential differences in mineral composition. +It might at first sight have been supposed that +the lavas of these two volcanic mountains—situated +at such a short distance from each other, and evidently +along the same line of fracture in the crust—would be +of the same general composition; but such is not the +case. In the lava of Vesuvius leucite is an essential, +and perhaps the most abundant mineral. It is called +by Zirkel <i>Sanidin-Leucitgestein</i>. (See <a href="#PLATE_4">Plate IV</a>.) +But in that of Etna this mineral is (as far as I am +aware) altogether absent. We have fortunately +abundant means of comparison, as the lavas of +these two mountains have been submitted to close +examination by petrologists. In the case of the +Vesuvian lavas, an elaborate series of chemical +analyses and microscopical observations have been +<span class="pagenum"><a name="Page_68" id="Page_68">[Pg 68]</a></span>made by the Rev. Professor Haughton, of Dublin +University, and the author,<a name="FNanchor_8_62" id="FNanchor_8_62"></a><a href="#Footnote_8_62" class="fnanchor">[8]</a> from specimens collected +by Professor Guiscardi from the lava-flows extending +from 1631 to 1868, in every one of which +leucite occurs, generally as the most abundant +mineral, always as an essential constituent. On +the other hand, the composition of the lavas of +Etna, determined by Professor A. von Lasaulx, from +specimens taken from the oldest (vorätnäischen) sheets +of lava down to those of the present day, indicates +a rock of remarkable uniformity of composition, in +which the components are plagioclase felspar, augite, +olivine, magnetite, and sometimes apatite; but of +leucite we have no trace.<a name="FNanchor_9_63" id="FNanchor_9_63"></a><a href="#Footnote_9_63" class="fnanchor">[9]</a> In fact, the lavas of Etna +are very much the same in composition as the ordinary +basalts of the British Isles, while those of Vesuvius +are of a different type. This seems to suggest an +origin of the two sets of lavas from a different deep-seated +magma; the presence of leucite in such large +quantity requiring a magma in which soda is in +excess, as compared with that from which the lavas +of Etna have been derived.<a name="FNanchor_10_64" id="FNanchor_10_64"></a><a href="#Footnote_10_64" class="fnanchor">[10]</a></p> + +<div class="footnote"><p><a name="Footnote_1_55" id="Footnote_1_55"></a><a href="#FNanchor_1_55"><span class="label">[1]</span></a> <i>Mémoires pour Servir</i>, etc., vol. ii.</p></div> + +<div class="footnote"><p><a name="Footnote_2_56" id="Footnote_2_56"></a><a href="#FNanchor_2_56"><span class="label">[2]</span></a> Daubeny, <i>Volcanoes</i>, p. 270.</p></div> + +<div class="footnote"><p><a name="Footnote_3_57" id="Footnote_3_57"></a><a href="#FNanchor_3_57"><span class="label">[3]</span></a> Von Waltershausen, <i>Der Ætna</i>, edited by A. von Lasaulx.</p></div> + +<div class="footnote"><p><a name="Footnote_4_58" id="Footnote_4_58"></a><a href="#FNanchor_4_58"><span class="label">[4]</span></a> Lyell, <i>Principles of Geology</i>, vol. ii., edition 1872.</p></div> + +<div class="footnote"><p><a name="Footnote_5_59" id="Footnote_5_59"></a><a href="#FNanchor_5_59"><span class="label">[5]</span></a> Its height, as determined by Captain Smyth in 1875 trigonometrically, +was 10,874 feet, and afterwards by Sir J. Herschel barometrically, +10,872 feet.</p></div> + +<div class="footnote"><p><a name="Footnote_6_60" id="Footnote_6_60"></a><a href="#FNanchor_6_60"><span class="label">[6]</span></a> <i>Atlas des Ætna</i> (Weimar, 1858), in which the different lava-streams +of 1688, 1802, 1809, 1811, 1819, 1824, and 1838 are delineated.</p></div> + +<div class="footnote"><p><a name="Footnote_7_61" id="Footnote_7_61"></a><a href="#FNanchor_7_61"><span class="label">[7]</span></a> Sir William Hamilton observes that history is silent regarding the +first eruptions of Etna. It was in activity before the Trojan War, and +even before the arrival of the "Sizilien" settlers. Diodorus and +Thucydides notice the earliest recorded eruptions, those from 772 to +388 <span class="smcap">B.C.</span>, during which time the mountain was thrice in eruption. +Later eruptions took place in the year <span class="smcap">140, 135, 125, 122 B.C.</span> In the +year 44 <span class="smcap">B.C.</span>, in the reign of Julius Cæsar, there was a very violent outburst +of volcanic activity.—<i>Neuere Beobachtungen über die Vulkane +Italiens und am Rhein</i>, p. 173, Frankfurt (1784).</p></div> + +<div class="footnote"><p><a name="Footnote_8_62" id="Footnote_8_62"></a><a href="#FNanchor_8_62"><span class="label">[8]</span></a> "Report on the Chemical and Mineralogical Characters of the +Lavas of Vesuvius from 1631 to 1868," <i>Transactions of the Royal Irish +Academy</i>, vol. xxvi. (1876). In the lava of 1848 leucite was found to +reach 44.9 per cent. of the whole mass. In that of Granatello, 1631, it +reaches its lowest proportion—viz., 3.37 per cent.</p></div> + +<div class="footnote"><p><a name="Footnote_9_63" id="Footnote_9_63"></a><a href="#FNanchor_9_63"><span class="label">[9]</span></a> A. von Lasaulx, in Von Waltershausen's <i>Der Ætna</i>, Book II., x. +423.</p></div> + +<div class="footnote"><p><a name="Footnote_10_64" id="Footnote_10_64"></a><a href="#FNanchor_10_64"><span class="label">[10]</span></a> The view of Professor Judd, that leucite easily changes into felspar, +and that some ancient igneous rocks which now contain felspar were +originally leucitic, does not seem to be borne out by the above facts. +In such cases the felspar crystals ought to retain the forms of leucite. +See <i>Volcanoes</i>, 4th edition, p. 268.</p></div> +<p><span class="pagenum"><a name="Page_69" id="Page_69">[Pg 69]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_II_CHAPTER_III" id="PART_II_CHAPTER_III"></a>CHAPTER III. +<br /><br /> +THE LIPARI ISLANDS, STROMBOLI.</h2> + + +<p>(<i>a.</i>) A brief account of this remarkable group of volcanic +islands must here be given, inasmuch as they seem +to be representatives of a stage of volcanic action in +which the igneous forces are gradually losing their +energy. According to Daubeny, the volcanic action in +these islands seems to be developed along two lines, +nearly at right angles to each other, one parallel to +that of the Apennines, beginning with Stromboli, +intersecting Panaria, Lipari, and Vulcano; the +other extending from Panaria to Salina, Alicudi, +and Felicudi, and again visible in the volcanic +products which make their appearance at Ustica. +(See <a href="#FIGURE_11">Map, Fig. 11</a>.) The islands lie between the +north coast of Sicily and that of Italy, and from +their position seem to connect Etna with Vesuvius; +but this is very problematical, as would appear from +the difference of their lavas. The principal islands +are those of Stromboli, Panaria, Lipari, Vulcano, +Salina, Felicudi, and Alicudi. These three last are +extinct or dormant, but Salina contains a crater, rising, +according to Daubeny, not less than 3500 feet above +the sea.<a name="FNanchor_1_65" id="FNanchor_1_65"></a><a href="#Footnote_1_65" class="fnanchor">[1]</a> Vulcano (referred to by Strabo under the +name of Hiera) consists of a crater which constantly +<span class="pagenum"><a name="Page_70" id="Page_70">[Pg 70]</a></span>emits large quantities of sulphurous vapours, but was +in a state of activity in the year 1786, when, after +frequent earthquake shocks and subterranean noises, +it vomited forth during fifteen days showers of sand, +together with clouds of smoke and flame, altering +materially the shape of the crater from which they +proceeded.</p> + +<div class="figcenter"> +<a name="FIGURE_11"> +<span class="center">LIPARI ISLANDS.</span><br /> + <img src="images/figure11.jpg" alt="Lipari Islands" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 11.</span>—Map to show the position of these islands, showing the +branching lines of volcanic action—one parallel to that of the Apennines, +the other stretching westwards at right angles thereto. +</td></tr> +</table> +</div> + +<p>The islands of Lipari are formed of beds of tuff, +penetrated by numerous dykes of lava, from which +uprise two or three craters, formed of pumice and +obsidian passing into trachyte. Volcanic operations +might have here been said to be extinct, were it not +that their continuance is manifested by the existence +<span class="pagenum"><a name="Page_71" id="Page_71">[Pg 71]</a></span>of hot springs and "stufes," or vapour baths, at St. +Calogero, about four miles from the town of Lipari. +Daubeny considers it not improbable that this island +may have had an active volcano even within the +historical period, a view which is borne out by the +statement of Strabo.<a name="FNanchor_2_66" id="FNanchor_2_66"></a><a href="#Footnote_2_66" class="fnanchor">[2]</a></p> + +<div class="figcenter"> +<a name="FIGURE_12"> + <img src="images/figure12.jpg" alt="Vulcano" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 12.</span>—Island of Vulcano, one of the Lipari Group, in eruption.—(After +Sir W. Hamilton.) +</td></tr> +</table> +</div> + +<p>(<i>b.</i>) But by far the most remarkable island of the +group, as regards its present volcanic condition, is +Stromboli, which has ever been in active eruption from +the commencement of history down to the present day. +Professor Judd, who visited this island in 1874, and +has produced a striking representation of its aspect,<a name="FNanchor_3_67" id="FNanchor_3_67"></a><a href="#Footnote_3_67" class="fnanchor">[3]</a> +gives an account of which I shall here avail myself.<a name="FNanchor_4_68" id="FNanchor_4_68"></a><a href="#Footnote_4_68" class="fnanchor">[4]</a> +<span class="pagenum"><a name="Page_72" id="Page_72">[Pg 72]</a></span>The island is of rudely circular outline, and rises into +a cone, the summit of which is 3090 feet above the +level of the Mediterranean. From a point on the side +of the mountain masses of vapour are seen to issue, +and these unite to form a cloud over the summit; the +outline of this vapour-cloud varying continually according +to the hygrometric state of the atmosphere, and +the direction and force of the wind. At the time of +Professor Judd's visit, the vapour-cloud was spread in +a great horizontal stratum overshadowing the whole +island; but it was clearly seen to be made up of a +number of globular masses, each of which is a product +of a distinct outburst of volcanic forces. Viewed +at night-time, Stromboli presents a far more striking +and singular spectacle. When watched from the +deck of a vessel, a glow of red light is seen to +make its appearance from time to time above the +summit of the mountain; it may be observed +to increase gradually in intensity, and then as +gradually to die away. After a short interval the +same appearances are repeated, and this goes on till +the increasing light of dawn causes the phenomenon +to be no longer visible. The resemblance presented +by Stromboli to a "flashing light" on a most gigantic +scale is very striking, and the mountain has long +been known as "the lighthouse of the Mediterranean."</p> + +<p>The mountain is built up of ashes, slag, and scoriæ, +to a height of (as already stated) over 3000 feet above +the surface of the sea; but, as Professor Judd observes, +this by no means gives a just idea of its vast bulk. +Soundings in the sea surrounding the island show +that the bottom gradually shelves around the shores +to a depth of nearly 600 fathoms, so that Stromboli is +a great conical mass of cinders and slaggy materials, +<span class="pagenum"><a name="Page_73" id="Page_73">[Pg 73]</a></span>having a height above its floor of about 6600 feet, +and a base the diameter of which exceeds four miles.</p> + +<p>The crater of Stromboli is situated, not at the apex +of the cone, but at a distance of 1000 feet below it. +The explosions of steam, accompanied by the roaring +as of a smelting furnace, or of a railway engine when +blowing off its steam, are said by Judd to take place +at very irregular intervals of time, "varying from less +than one minute to twenty minutes, or even more." +On the other hand, Hoffmann describes them as +occurring at "perfectly regular intervals," so that, +perhaps, some variation has taken place within the +interval of about forty years between each observation. +Both observers agree in stating that lava is to +be seen welling up from some of the apertures within +the crater, and pouring down the slope towards the +sea, which it seldom or never reaches.<a name="FNanchor_5_69" id="FNanchor_5_69"></a><a href="#Footnote_5_69" class="fnanchor">[5]</a> The intermittent +character of these eruptions appears to be +due, as Mr. Scrope has suggested, to the exact proportion +between the expansive and repressive forces; +the expansive force arising from the generation of a +certain amount of aqueous vapour and of elastic gas; +the repressive, from the pressure of the atmosphere +and from the weight of the superincumbent volcanic +products. Steam is here, as in a steam-engine, not +the originating agent in the phenomena recorded; +but the result of water coming in contact with +molten lava constantly welling up from the interior, +by which it is converted into steam, which from time +to time acquires sufficient elastic force to produce the +eruptions; the water being obviously derived from +the surrounding sea, which finds its way by filtration +through fissures, or through the porous mass of which +<span class="pagenum"><a name="Page_74" id="Page_74">[Pg 74]</a></span>the mountain is formed. Were it not for the access +of water this volcano would probably appear as a +fissure-cone extruding a small and continuous stream +of molten lava. The adventitious access of the sea +water gives rise to the phenomena of intermittent +explosions. The vitality of the volcano is therefore +due, not to the presence of water, but to the welling +up of matter from the internal reservoir through the +throat of the volcano.</p> + +<p><i>Pantelleria.</i>—This island, lying between the coast +of Sicily and Cape Bon in Africa, is wholly volcanic. +It has a circumference of thirty miles, and from its +centre rises an extinct crater-cone to a height of about +3000 feet. The flanks of this volcano are diversified +by several fresh craters and lava-streams, while hot +springs burst out with a hissing noise on its southern +flank, showing that molten matter lies below at no +very great depth.</p> + +<p>This island probably lies along the dividing line +between the non-volcanic and volcanic region of the +Mediterranean, and is consequently liable to intermittent +eruptions. It was at a short distance from +this island that the remarkable submarine outburst +of volcanic forces took place on October 17th, 1891, +for an account of which we are indebted to Colonel +J. C. Mackowen.<a name="FNanchor_6_70" id="FNanchor_6_70"></a><a href="#Footnote_6_70" class="fnanchor">[6]</a> On that day, after a succession of +earthquake shocks, the inhabitants were startled by +observing a column of "smoke" rising out of the sea at +a distance of three miles, in a north-westerly direction. +<span class="pagenum"><a name="Page_75" id="Page_75">[Pg 75]</a></span>The Governor, Francesco Valenza, having manned a +boat, rowed out towards the fiery column, and on +arriving found it to consist of black scoriaceous bombs, +which were being hurled into the air to a height of +nearly thirty yards; some of them burst in the air, +others, discharging steam, ran hissing over the water; +many of them were very hot, some even red-hot. One +of these bombs, measuring two feet in diameter, was +captured and brought to shore. It was observed that +after the eruption the earthquake shocks ceased. A +vast amount of material was cast out of the submarine +crater, forming an island 500 yards in length +and rising up to nine feet above the surface, but after +a few days it was broken up and dispersed over +the sea-bed by the action of the waves.</p> + +<div class="footnote"><p><a name="Footnote_1_65" id="Footnote_1_65"></a><a href="#FNanchor_1_65"><span class="label">[1]</span></a> <i>Volcanoes</i>, p. 262. These islands are described by Hoffmann, +<i>Poggendorf Annal.</i>, vol. xxvi. (1832); also by Lyell, <i>Principles of +Geology</i>, vol. ii., and by Judd, who personally visited them, and gives +a very vivid account of their appearance and structure.</p></div> + +<div class="footnote"><p><a name="Footnote_2_66" id="Footnote_2_66"></a><a href="#FNanchor_2_66"><span class="label">[2]</span></a> Strabo, lib. vi.</p></div> + +<div class="footnote"><p><a name="Footnote_3_67" id="Footnote_3_67"></a><a href="#FNanchor_3_67"><span class="label">[3]</span></a> Judd, <i>Volcanoes</i>, p. 8.</p></div> + +<div class="footnote"><p><a name="Footnote_4_68" id="Footnote_4_68"></a><a href="#FNanchor_4_68"><span class="label">[4]</span></a> Stromboli has also been described by Spallanzani, Hoffmann, +Daubeny, and others. The account of Judd is the most recent. Of +this island Strabo says, "Strongyle a rotundate figuræ sic dicta, ignita +ipsa quoque, violentia flammarum minor, fulgore excellens; ibi habitasse +Æcolum ajunt."—Lib. vi.</p></div> + +<div class="footnote"><p><a name="Footnote_5_69" id="Footnote_5_69"></a><a href="#FNanchor_5_69"><span class="label">[5]</span></a> <i>Poggend. Annal.</i>, vol. xxvi., quoted by Daubeny.</p></div> + +<div class="footnote"><p><a name="Footnote_6_70" id="Footnote_6_70"></a><a href="#FNanchor_6_70"><span class="label">[6]</span></a> Communicated by Captain Petrie to the Victoria Institute, 1st +February 1892. See also a detailed and illustrated account of the +eruption communicated by A. Ricco to the <i>Annali dell' Ufficio centrale +Meteorologico e Geodonamico</i>, Ser. ii., Parte 3, vol. xi. Summarised by +Mr. Butler in <i>Nature</i>, April 21, 1892.</p></div> +<p><span class="pagenum"><a name="Page_76" id="Page_76">[Pg 76]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_II_CHAPTER_IV" id="PART_II_CHAPTER_IV"></a>CHAPTER IV. +<br /><br /> +THE SANTORIN GROUP.</h2> + + +<div class="figcenter"> +<a name="FIGURE_13"> + <img src="images/figure13.jpg" alt="Section of Santorin" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 13.</span>—Ideal Section through the Gulf of Santorin, to show the +structure of the submerged volcano.—<i>a.</i> Island of Aspronisi; <i>b.</i> Island +of Thera; 1. Old Kaimeni Island; 2. New Kaimeni Island; 3. Little +Kaimeni Island. +</td></tr> +</table> +</div> + +<p>(<i>a.</i>) Before leaving the subject of European active +volcanoes, it is necessary to give some account of the +remarkable volcanic island of Santorin, in the Grecian +archipelago. This island for 2000 years has been the +scene of active volcanic operations, and in its outline +and configuration, both below and above the surface +of the Mediterranean, presents the aspect of a +partially submerged volcanic mountain. (See <a href="#FIGURE_13">Section, +Fig. 13</a>.) If, for example, we can imagine the waters +of the sea to rise around the flanks of Vesuvius until +they have entered and overflowed to some depth the +interior caldron of Somma, thus converting the old +crater into a crescent-shaped island, and the cone of +Vesuvius into an island—or group of islands—within +<span class="pagenum"><a name="Page_77" id="Page_77">[Pg 77]</a></span>the caldron, then we shall form some idea of the +appearance and structure of the Santorin group.</p> + +<p><i>Form of the Group.</i>—The principal island, Thera, +has somewhat the shape of a crescent, breaking off in +a precipitous cliff on the inner side, but on the outer +side sloping at an angle of about fifteen degrees into +deep water. Continuing the curvature of the crescent, +but separated by a channel, is the island of Therasia; +and between this and the southern promontory of +Thera is another island called Aspronisi. All these +islands, if united, would form the rim of a crater, in +which the volcanic matter slopes outward into deep +water, descending at a short distance to a depth +of 200 fathoms and upwards. In the centre of the +gulf thus formed rise three islands, called the Old, +New, and Little Kaimenis. These may be regarded as +cones of eruption, which history records as having +been thrown up at successive intervals. According to +Pliny, the year 186 <span class="smcap">B.C.</span> gave birth to Old Kaimeni, +also called Hiera, or the Sacred Isle; and in the first +year of our era Thera (the Divine) made its appearance +above the water, and was soon joined to the +older island by subsequent eruptions. Old Kaimeni +also increased in size by the eruptions of 726 and +1427. A century and a half later, in 1573, another +eruption produced the cone and crater called Micra-Kaimeni. +Thus were formed, or rather were rendered +visible above the water, the central craters of eruption; +and between these and the inner cliff of Thera +and Therasia is a ring of deep water, descending to a +depth of over 200 fathoms. So that, were these islands +raised out of the sea, we should have presented to our +view a magnificent circular crater about six miles in +diameter, bounded by nearly vertical walls of rock +<span class="pagenum"><a name="Page_78" id="Page_78">[Pg 78]</a></span>from 1000 to 1500 feet in height, and ruptured at one +point, from the centre of which would rise two volcanic +cones—namely, the Kaimenis—one with a double +crater, still foci of eruption, and from time to time +bursting forth in paroxysms of volcanic energy, of +which those of 1650, 1707, and 1866 were the most +violent and destructive.<a name="FNanchor_1_71" id="FNanchor_1_71"></a><a href="#Footnote_1_71" class="fnanchor">[1]</a> Of this last I give a bird's-eye +view (<a href="#FIGURE_14">Fig. 14</a>).</p> + +<p>The only rock of non-volcanic origin in these +islands consists of granular limestone and clay slate +forming the ridge of Mount St. Elias, which rises to +a height of 1887 feet at the south-eastern side of +the island of Thera, crossing the island from its +outer margin nearly to the interior cliff, so that the +volcanic materials have been piled up along its sides. +The rocks of St. Elias are much more ancient than +any of the volcanic materials around; and, as Bory +St. Vincent has shown, have been subjected to the +same flexures, dip and strike, as those sedimentary +rocks which go to form the non-volcanic islands of +the Grecian archipelago.</p> + +<p><span class="pagenum"><a name="Page_79" id="Page_79">[Pg 79]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_14"> + <img src="images/figure14.jpg" alt="Gulf of Santorin" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 14.</span>—Bird's-eye View of the Gulf of Santorin during the volcanic eruption of February 1866.—(After Lyell.) +<p><span class="pagenum"><a name="Page_80" id="Page_80">[Pg 80]</a></span></p> +</td></tr> +</table> +</div> + +<div class="figcenter"> +<a name="FIGURE_15"> + <img src="images/figure15.jpg" alt="Rocca Monfina" /> +</a> +<p class="center"><i>Ground Plan of Rocca Monfina</i></p> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 15.</span>—Rocca Monfina, in Southern Italy, showing a crater-ring +of trachytic tuffs, from the midst of which, according to Judd, an andesite +lava-cone has been built up. Compare with the Santorin Group. +</td></tr> +</table> +</div> + +<p>(<i>b.</i>) <i>Origin of the Santorin Group.</i>—In reference to +the origin of the Santorin group, Lyell regards it +as a remnant of a great volcanic mountain which +possessed a focus of eruption rising in the position +of the present foci, but afterwards partially destroyed +and the whole submerged to a depth of over 1000 +feet. But another explanation is open to us, and +one not inconsistent with what we now know of +the physical changes to which the Mediterranean has +been subjected since early Tertiary times. To my +mind it is difficult to conceive how such a volcanic +mountain as that of Santorin could have been formed +under water; while, on the other hand, its physical +structure and contour bear so striking a resemblance +(as already observed) to those of Vesuvius and Rocca +Monfina that we are much tempted to infer that it +had a somewhat similar origin. Now we know that +Vesuvius was built up by means of successive eruptions +taking place under the air; and the question arises +whether it could be possible that Santorin had a similar +origin owing to the waters of the Mediterranean +having been temporally lowered at a later Tertiary +epoch. It has been stated by M. Fouqué that the +age of the more ancient volcanic beds of Santorin +belong, as shown by the included fossils, to the +<span class="pagenum"><a name="Page_81" id="Page_81">[Pg 81]</a></span>newer Pliocene epoch. These are of course the +unsubmerged, and therefore more recent strata, and +may have been recently upheaved during one or more +of the outbursts of volcanic energy. But it seems +an impossibility that the Gulf of Santorin, with its +precipitous walls and deep circular interior channel, +as shown by the Ideal Section (<a href="#FIGURE_13">Fig. 13</a>), could have +been formed otherwise than under the air. We are +led, therefore, to inquire whether there was a time +in the history of the Mediterranean, since the Eocene +period, when the waters were lower than at present. +That this was the case we have clear evidence. The +remains of elephants, hippopotami, and other animals, +which have been discovered in great numbers in the +Maltese caves, show that this island was united to +Sicily, and this again to Europe, during the later +Pliocene epoch, so as to have become the abode of +an Europasian fauna. According to Dr. Wallace, a +causeway of dry land existed, stretching from Italy to +Tunis in North Africa through the Maltese Islands—an +inference involving the lowering of the waters of the +Mediterranean by several hundred feet.<a name="FNanchor_2_72" id="FNanchor_2_72"></a><a href="#Footnote_2_72" class="fnanchor">[2]</a> There is +every reason for supposing that the old volcano of +Santorin was in active eruption at this period; and +its history may be considered to be similar to that of +Vesuvius until, at the rising of the waters during the +Pluvial (or Post-Pliocene) epoch, during which they +rose higher than at present, Santorin was converted +into a group of islands, slightly differing in form from +those of the present day. This view seems to meet the +difficulties regarding the origin of this group, difficulties +which Lyell had long since clearly recognised.</p> + +<p><span class="pagenum"><a name="Page_82" id="Page_82">[Pg 82]</a></span></p><p>(<i>c.</i>) <i>Limit of the Mediterranean Volcanic Region.</i>—With +the Santorin group we conclude our account of +the active European volcanoes. It may be observed, +however, that from some cause not ascertained the volcanic +districts of the Mediterranean and its shores are +confined to the north side of that great inland sea; so +that as regards vulcanicity the African coast presents +a striking contrast to that of the opposite side. If we +draw a line from the shores of the Levant to the +Straits of Gibraltar, by Candia, Malta, and to the +south of Pantelleria and Sardinia, we shall find that +the volcanic islands and districts of the mainland lie +to the north of it.<a name="FNanchor_3_73" id="FNanchor_3_73"></a><a href="#Footnote_3_73" class="fnanchor">[3]</a> This has doubtless some connection +with the internal geological structure. The +immunity of the Libyan desert from volcanic irruptions +is in keeping with the remarkably undisturbed +condition of the Secondary strata, which seldom +depart much from the horizontal position; while the +igneous rocks of the Atlas mountains are probably of +great geological antiquity. On the other hand, the +Secondary and Tertiary formations of the northern +shores and islands of the Mediterranean are generally +characterised by the highly-inclined, flexured, and +folded position of the strata. Hence we may +suppose that the crust over the region lying to the +north of the volcanic line, owing to its broken and +<span class="pagenum"><a name="Page_83" id="Page_83">[Pg 83]</a></span>ruptured condition, was less able to resist the +pressure of the internal forces of eruption than that +lying to the south of it; and that, in consequence, +vents and fissures of eruption were established over +the former of these regions, while they are absent in +the latter.</p> + +<div class="footnote"><p><a name="Footnote_1_71" id="Footnote_1_71"></a><a href="#FNanchor_1_71"><span class="label">[1]</span></a> Fuller details will be found in Daubeny's <i>Volcanoes</i>, chap. xviii., +and Lyell's <i>Principles of Geology</i>, vol. ii. p. 65 (edition 1872). The +bird's-eye view is taken from this latter work by kind permission of the +publisher, Mr. J. Murray, as also the accompanying Ideal Section, +<a href="#FIGURE_13">Fig. 13</a>.</p></div> + +<div class="footnote"><p><a name="Footnote_2_72" id="Footnote_2_72"></a><a href="#FNanchor_2_72"><span class="label">[2]</span></a> Wallace, <i>Geographical Distribution of Animals</i> (1876). The +author's <i>Sketch of Geological History</i>, p. 130 (Deacon & Co., 1887).</p></div> + +<div class="footnote"><p><a name="Footnote_3_73" id="Footnote_3_73"></a><a href="#FNanchor_3_73"><span class="label">[3]</span></a> The <i>volcanic area</i> lying to the north of this line will include +Sardinia, Sicily, Pantelleria, the Grecian Archipelago, Asia Minor, and +Syria; the <i>non-volcanic area</i> lying to the south of this line will include +the African coast, Malta, Isles of Crete and Cyprus. The Isle of +Pantelleria is apparently just on the line, which, continued eastward, +probably follows the north coast of Cyprus, parallel to the strike +of the strata and of the central axis of that island.—See "Carte +Géologique de l'île de Chypre, par MM. Albert Gaudry et Amedée +Damour" (1860).</p></div> +<p><span class="pagenum"><a name="Page_84" id="Page_84">[Pg 84]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_II_CHAPTER_V" id="PART_II_CHAPTER_V"></a>CHAPTER V. +<br /><br /> +EUROPEAN EXTINCT OR DORMANT VOLCANOES.</h2> + + +<p>We are naturally led on from a consideration of the +active volcanoes of Europe to that of volcanoes which +are either dormant or extinct in the same region. +Such are to be found in Italy, Central France, +both banks of the Rhine and Moselle, the Westerwald, +Vogelsgebirge, and other districts of Germany; +in Hungary, Styria, and the borders of the Grecian +archipelago. But the subject is too large to be +treated here in detail; and I propose to confine my +observations to some selected cases which are to be +found in Southern Italy, Central France, and the +Rhenish districts, where the volcanic features are of +so recent an age as to preserve their outward form +and structure almost intact.</p> + +<p>(<i>a.</i>) <i>Southern Italy.</i>—Extinct volcanoes and volcanic +rocks occupy considerable tracts between the western +flanks of the Apennines and the Mediterranean coast +in the Neapolitan and Roman States, forming the +remarkable group of the Phlegræan fields (Campi +Phlegræi), with the adjoining islands of Ischia, +Procida, Nisida, Vandolena, Ponza, and Palmarola; +at Melfi and Avellino. All the region around Rome +extending along the western slopes of the Apennines +from Velletri to Orvieto, together with Mount Annato +<span class="pagenum"><a name="Page_85" id="Page_85">[Pg 85]</a></span>in Tuscany, is formed of volcanic material, and the +same may be said of a large part of the island of +Sardinia. From these districts I shall select some +points which seem to be of special interest.</p> + +<p><i>Monte Nuovo and the Phlegræan Fields.</i>—The tract +of which this celebrated district forms a part lies as +it were in a bay of the Apennine limestone of Jurassic +age. The floor of this bay is composed of puzzolana, +a name given to beds of volcanic tuff of great thickness, +and rising into considerable hills in the vicinity +of the city of Naples, such as that of St. Elmo. Its +composition is peculiar, as it is chiefly formed of +small pieces of pumice, obsidian, and trachyte, in beds +alternating with loam, ferriferous sand, and fragments +of limestone. It is evidently of marine formation, +as Sir William Hamilton, Professor Pilla, and others +have detected sea-shells therein, of the genera <i>Ostræa</i>, +<i>Cardium</i>, <i>Pecten</i> and <i>Pectunculus</i>, <i>Buccinum</i>, etc. It +is generally of a greyish colour, and sometimes +sufficiently firm to be used as a building stone. The +Roman Campagna is largely formed of similar +materials, which were deposited at a time when the +districts in question were submerged, and matter was +being erupted from volcanic vents at various points +around, and spread over the sea-bed.</p> + +<p>Such is the character of the general floor on +which the more recent crater-cones of this district +have been built. These are numerous, and all +extinct with the exception of the Solfatara, near +Puzzuoli, from which gases mixed with aqueous +vapour are continually being exhaled. The gases +consist of sulphuretted hydrogen mixed with a minute +quantity of muriatic acid.<a name="FNanchor_1_74" id="FNanchor_1_74"></a><a href="#Footnote_1_74" class="fnanchor">[1]</a> This district is also +<span class="pagenum"><a name="Page_86" id="Page_86">[Pg 86]</a></span>remarkable for containing several lakes occupying +the interiors of extinct craters; amongst others, Lake +Avernus, which, owing to its surface having been +darkened by forests, and in consequence of the +effluvia arising from its stagnant waters, has had +imparted to it a character of gloom and terror, so +that Homer in the <i>Odyssey</i> makes it the entrance to +hell, and describes the visit of Ulysses to it. Virgil +follows in his steps. Another lake of similar origin +is Lake Agnano. Here also is the Grotto del Cane, +a cavern from which are constantly issuing volumes +of carbonic acid gas combined with much aqueous +vapour, which is condensed by the coldness of the +external air, thus proving the high temperature of +the ground from which the gaseous vapour issues. +This whole volcanic region, so replete with objects +of interest,<a name="FNanchor_2_75" id="FNanchor_2_75"></a><a href="#Footnote_2_75" class="fnanchor">[2]</a> may be considered, as regards its volcanic +character, in a moribund condition; but that it is +still capable of spasmodic movement is evinced by +the origin of Monte Nuovo, the most recent of the +crater-cones of the district. This mountain, rising +from the shore of the Bay of Baiæ, was suddenly +formed in September 29th, 1538, and rises to a height +of 440 feet above the sea-level. It is a crater-cone, +and the depth of the crater has been determined by +the Italian mineralogist Pini to be 421 English feet; +its bottom is thus only 19 feet above the sea-level. A +portion of the base of the cone is considered partly +to occupy the site of the Lucrine Lake, which was +itself nothing more than the crater of a pre-existent +<span class="pagenum"><a name="Page_87" id="Page_87">[Pg 87]</a></span>volcano, and was almost entirely filled up during the +explosion of 1538. Monte Nuovo is composed of +ashes, lapilli, and pumice-stones; and its sudden +formation, heralded by earthquakes, and accompanied +by the ejection of volcanic matter mixed with fire +and water, is recorded by Falconi, who vividly depicts +the terror and consternation of the inhabitants of the +surrounding country produced by this sudden and +terrible outburst of volcanic forces.<a name="FNanchor_3_76" id="FNanchor_3_76"></a><a href="#Footnote_3_76" class="fnanchor">[3]</a></p> + +<p>(<i>b.</i>) <i>Central Italy and the Roman States.</i>—The tract +bordering the western slopes of the Apennines northward +from Naples into Tuscany, and including the +Roman States, is characterised by volcanic rocks and +physical features of remarkable interest and variety. +These occur in the form of extinct craters, sometimes +filled with water, and thus converted into circular +lakes; or of extensive sheets and conical hills of tuff; +or, finally, of old necks and masses of trachyte and +basalt, sometimes exhibiting the columnar structure. +The Eternal City itself is built on hills of +volcanic material which some observers have supposed +to be the crater of a great volcano; but +Ponzi, Brocchi, and Daubeny all concur in the +opinion that this is not the case, as will clearly +appear from the following account.</p> + +<p>The geological structure of the valley of the Tiber +at Rome is very clearly described by Professor Ponzi +in a memoir published in 1850, from which the +accompanying section is taken.<a name="FNanchor_4_77" id="FNanchor_4_77"></a><a href="#Footnote_4_77" class="fnanchor">[4]</a> (<a href="#FIGURE_16">Fig. 16</a>.) From +this it will be seen that "the Seven-hilled City" +<span class="pagenum"><a name="Page_88" id="Page_88">[Pg 88]</a></span>is built upon promontories of stratified volcanic tuff, +of which the Campagna is formed, breaking off along +the banks of the Tiber, the hills being the result of +the erosion, or denudation, of the strata along the side +of the river valley. As the strata dip from west to +east across the course of the river, it follows that +those on the western banks are below those on the +opposite side; and thus the marine sands and marls +which underlie the volcanic tuff, and are concealed +by it along the eastern side of the valley, emerge on +the west, and form the range of hills on that side. +Such being the structure of the formations under +Rome, it is evident that it is not "built on a +volcano."</p> + +<div class="figcenter"> +<a name="FIGURE_16"> + <img src="images/figure16.jpg" alt="Valley of Tiber" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 16.</span>—Geological Section across the Valley of the Tiber at Rome. +1. Alluvium of the Tiber; 2. Diluvium; 3. Volcanic tuff (recent +deposits); 4. Sands, etc.; 5. Blue marl (sub-Apennine deposits). +</td></tr> +</table> +</div> + + +<p>The tuff contains fragments of lava and pebbles +of Apennine limestone, and was deposited under +the waters of an extensive lake at a time when +volcanic action was rife amidst the Alban Hills. +This lacustrine formation rests in turn on deposits +of marine origin, containing oysters, patellæ, and +other sea-shells, of which the chain of hills on the +right bank of the Tiber is chiefly formed.</p> + +<p>The district around Albano lying to the south of +Rome is of peculiar interest from the assemblage of +old crater-lakes which it contains; as, for instance, +<span class="pagenum"><a name="Page_89" id="Page_89">[Pg 89]</a></span>those of Albano, Vallariccia, Nemi, Juturna, and the +lake of Gabii. The lake of Albano, one of the most +beautiful sheets of water in the world, is about six +miles in circumference, and surrounded by beds of +peperino, a variety of tuff presenting a bright, undecomposed +aspect when newly broken. The level of +this lake was lowered by the Romans during the +siege of Veii by means of a tunnel, so that the waters +are 200 feet lower than the level at which they +originally stood. In the same district is the lake of +Nemi, very regular in its circular outline; that of +Juturna lying near the foot of the Alban Hills, and +that of Ariccia lying in a deep hollow eight miles in +circumference;—all may be supposed to have been the +craters of extinct volcanoes, both by reason of their +shape and of the materials of which they are formed. +All these old craters are, however, according to +Daubeny, "only the dependencies and offshoots, as +it were, of the great extinct volcano, the traces of +which still remain upon the summit of the Alban +Hills, and which is comparable in its form to that +of Vesuvius, as it is surrounded by an outer circle +of volcanic rock comparable to that of Somma."<a name="FNanchor_5_78" id="FNanchor_5_78"></a><a href="#Footnote_5_78" class="fnanchor">[5]</a></p> + +<p>To the north of the city of Rome are several crateriform +lakes, some of which are of great size, such as +that of Bolsena, over twenty miles in circumference, +and the Lago di Bracciano, almost as large, and lying +about twelve miles from the city. These extensive +sheets of water are surrounded by banks of tuff and +volcanic sand, in which fragments of augite, leucite, +and crystals of titanite are distributed. The town of +Viterbo is built up at the foot of a steep hill called +Monte Cimini, the lower part of which is composed +<span class="pagenum"><a name="Page_90" id="Page_90">[Pg 90]</a></span>of trachyte; this is surmounted by tuff, which appears +to have been ejected from an extinct crater +occupying the summit of the mountain, and now +converted into a lake called the Lake of Vico. This +crater is perfectly circular, and from its centre rises a +little conical hill covered by trees.</p> + +<p>(<i>c.</i>) <i>Physical History.</i>—Space does not permit of a +fuller description of the remarkable volcanic features +of the tract lying along the western slope of the +Apennines; but from what has been stated it will be +clear that volcanic forces have been in operation at one +time on a grand scale in the Roman States and the +South of Tuscany, over a tract extending from Mount +Annato to Velletri and Segni.</p> + +<p>This tract was separated from that of the Neapolitan +volcanic region by a range of limestone +hills of Jurassic age between Segni and Gaeta, a +protrusion of the Alban Hills westward; but the +general structure and physical history of both regions +are probably very similar, with the exception that the +igneous forces still retain their vitality in the more +southerly region. In the case of the Roman volcanic +district, a bay seems to have been formed about the +close of the Miocene period, bounded on all sides but +the west by hills of limestone, over whose bed strata +of marl, sandstone, and conglomerate were deposited. +This tract was converted by subsequent movements +into a fresh-water lake, and contemporaneously +volcanic operations commenced over the whole +region, and beds of tuff, often containing blocks of +rock ejected from neighbouring craters, were deposited +over those of marine origin. Meanwhile numerous +crater-cones were thrown up; and, as the land gradually +rose, the waters of the lake were drained off, +<span class="pagenum"><a name="Page_91" id="Page_91">[Pg 91]</a></span>leaving dry the Campagna and plain of the Tiber. +Ultimately the volcanic fires smouldered down and +died out, whether within the historic epoch or not +is uncertain; lakes were formed within the now +dormant craters, and the face of nature gradually +assumed a more placid and less forbidding aspect +over this memorable region, destined to be the site +of Rome, the Mistress of the World.</p> + +<div class="footnote"><p><a name="Footnote_1_74" id="Footnote_1_74"></a><a href="#FNanchor_1_74"><span class="label">[1]</span></a> As determined by Daubeny in 1825.</p></div> + +<div class="footnote"><p><a name="Footnote_2_75" id="Footnote_2_75"></a><a href="#FNanchor_2_75"><span class="label">[2]</span></a> Including the ruins of the Temple of Serapis, whose pillars are +perforated by marine boring shells up to a height of about 16 feet from +their base; indicating that the land had sunk down beneath the sea, +and afterwards been elevated to its present level.</p></div> + +<div class="footnote"><p><a name="Footnote_3_76" id="Footnote_3_76"></a><a href="#FNanchor_3_76"><span class="label">[3]</span></a> The account of Falconi, and another by Pietro Giacomo di Toledo, +are given by Sir W. Hamilton, <i>op. cit.</i>, p. 198, and also reproduced +by Sir C. Lyell, <i>Principles</i>, vol. i. p. 608.</p></div> + +<div class="footnote"><p><a name="Footnote_4_77" id="Footnote_4_77"></a><a href="#FNanchor_4_77"><span class="label">[4]</span></a> Guiseppe Ponzi, "Sulla storia fisica del Bacino di Roma," +<i>Annali di Scienze Fisiche</i> (Roma, 1850).</p></div> + +<div class="footnote"><p><a name="Footnote_5_78" id="Footnote_5_78"></a><a href="#FNanchor_5_78"><span class="label">[5]</span></a> Daubeny, <i>Volcanoes</i>, p. 171.</p></div> +<p><span class="pagenum"><a name="Page_92" id="Page_92">[Pg 92]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_II_CHAPTER_VI" id="PART_II_CHAPTER_VI"></a>CHAPTER VI. +<br /><br /> +EXTINCT VOLCANOES OF CENTRAL FRANCE.</h2> + + +<p>(<i>a.</i>) <i>General Structure of the Auvergne District.</i>—From +a granitic and gneissose platform situated near +the centre of France, and separated from the western +spurs of the Alps by the wide valley of the Rhone, +there rises a group of volcanic mountains surpassing +in variety of form and structure any similar mountain +group in Europe, and belonging to an epoch ranging +from the Middle Tertiary down almost to the present +day. This volcanic group of mountains gives rise to +several important rivers, such as the Loire, the Allier, +the Soule (a branch of the Loire), the Creuse, the +Dordogne, and the Lot; and in the Plomb du Cantal +attains an elevation of 6130 feet above the sea. Its +southern section, that of Mont Dore, the Cantal, +and the Haute Loire, is characterised by magnificent +valleys, traversing plateaux of volcanic lava, and +exhibiting the results of river erosion on a grand +scale; while its northern section, that of the Puy de +Dôme, presents to us a varied succession of volcanic +crater-cones and domes, with their extruded lava-streams, +almost as fresh and unchanged in form as +if they had only yesterday become extinct. A somewhat +similar, but less important, chain of extinct +volcanoes also occurs in the Velay and Vivarais, +<span class="pagenum"><a name="Page_93" id="Page_93">[Pg 93]</a></span>between the upper waters of the Loire and the +Allier, in the vicinity of the town of Le Puy.<a name="FNanchor_1_79" id="FNanchor_1_79"></a><a href="#Footnote_1_79" class="fnanchor">[1]</a> The +principal city in this region is Clermont-Ferrand, +lying near the base of the Puy de Dôme, and ever +memorable as the birthplace of Blaise Pascal.<a name="FNanchor_2_80" id="FNanchor_2_80"></a><a href="#Footnote_2_80" class="fnanchor">[2]</a></p> + +<div class="figcenter"> +<a name="FIGURE_17"> + <img src="images/figure17.jpg" alt="Generalised Section" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 17.</span>—Generalised Section through the Puy de Dôme and Vale +of Clermont, distance about ten miles. The general floor formed of +granite and gneiss (G); D. Domite-lava of the Puy de Dôme; Sc. +Cones of ashes and scoriæ; L. Lava-sheets; A. Alluvium of the Vale +of Clermont and Lake deposits. +</td></tr> +</table> +</div> + +<p>The physical structure of this region is on the +whole very simple. The fundamental rocks consist +of granite and gneiss passing into schist, all of +extreme geological antiquity, forming a vast platform +gradually rising in a southerly direction towards +<span class="pagenum"><a name="Page_94" id="Page_94">[Pg 94]</a></span>the head waters of the Loire and the Allier in the +Departments of Haute Loire, Lozère, and Ardèche. +On this platform are planted the whole of the volcanic +mountains. (See <a href="#FIGURE_17">Fig. 17</a>.)</p> + +<p>The granitic plateau is bounded on the east, +throughout a distance of about 50 miles, by the +wide and fertile plain of Clermont, watered by the +Allier and its numerous branches descending from the +volcanic mountains, and is about 25 miles in width +from east to west in the parallel of Clermont, but +gradually narrowing in a southerly direction, till +at Brioude it becomes an ordinary mountain ravine. +The eastern margin of the plain is formed by another +granitic ridge expanding into a plateau towards the +south, and joining in with that already described; +but towards the north and directly east of Clermont +it forms a high ridge traversed by the railway to St. +Étienne and Lyons, and descending towards the east +into the valley of the Loire. No more impressive +view is to be obtained of the volcanic region than +that from the summit of this second ridge, on arriving +there towards evening from the city of Lyons. At +your feet lies the richly-cultivated plain of Clermont, +dotted with towns, villages, and hamlets, and decorated +with pastures, orchards, vineyards, and numerous trees; +while beyond rises the granitic plateau, breaking off +abruptly along the margin of the plain, and deeply +indented by the valleys and gorges along which the +streams descend to join the Allier. But the chief +point of interest is the chain of volcanic crater-cones +and dome-shaped eminences which rise from the +plateau, amongst which the Puy de Dôme towers +supreme. Their individual forms stand out in clear and +sharp relief against the western sky, and gradually +<span class="pagenum"><a name="Page_95" id="Page_95">[Pg 95]</a></span>fade away towards the south into the serried masses +of Mont Dore and Cantal, around whose summits the +evening mists are gathering. Except the first view +of the Mont Blanc range from the crest of the Jura, +there is no scene perhaps which is calculated to +impress itself more vividly on the memory than that +here faintly described.<a name="FNanchor_3_81" id="FNanchor_3_81"></a><a href="#Footnote_3_81" class="fnanchor">[3]</a></p> + +<div class="figcenter"> +<a name="FIGURE_18"></a> +<a href="images/figure18full.jpg"> + <img src="images/figure18.jpg" alt="Transverse view" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 18.</span>—Transverse view of the Puy de Dôme and neighbouring volcanoes from the Puy de Chopine.—(After Scrope.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_96" id="Page_96">[Pg 96]</a></span></p><p>(<i>b.</i>) <i>The Vale of Clermont.</i>—The plain upon which +we look down was once the floor of an extensive lake, +for it is composed of various strata of sand, clay, +marl, and limestone, containing various genera and +species of fresh-water shells. These strata are of +great thickness, perhaps a thousand feet in some +places; and along with such shells as <i>Paludina</i>, <i>Planorbis</i>, +and <i>Limnæa</i> are also found remains of various +other animals, such as fish, serpents, batrachians, +crocodiles, ruminants, and those of huge pachyderms, +as <i>Rhinoceros</i>, <i>Dinotherium</i>, and <i>Cænotherium</i>. This +great lake, occupying a hollow in the old granitic platform +of Central France, must have been in existence +for an extensive period, which MM. Pomel, Aymard, +and Lyell all unite in referring to that of the Lower +Miocene. But what is to us of special interest is the +fact that, in the deposits of this lake of the Haute Loire, +with the exception of the very latest, there is no intermixture +of volcanic products such as might have been +expected to occur if the neighbouring volcanoes +had been in activity during its existence. Hence it +may be supposed that, as Scrope suggested, the +<span class="pagenum"><a name="Page_97" id="Page_97">[Pg 97]</a></span>waters of the lake were drained off owing to the +disturbance in the levels of the country caused by the +first explosions of the Auvergne volcanoes.<a name="FNanchor_4_82" id="FNanchor_4_82"></a><a href="#Footnote_4_82" class="fnanchor">[4]</a> If this be +so, then we possess a key by which to determine the +period of the first formation of volcanoes in Central +France; for, as the animal remains enclosed in the +lacustrine deposits of the Vale of Clermont belong +to the early Miocene stage, and the earliest traces of +contemporaneous volcanic <i>ejecta</i> are found only in +the uppermost deposits, we may conclude that the +first outburst of volcanic action occurred towards the +close of the Miocene period—a period remarkable for +similar exhibitions of internal igneous action in other +parts of the world.</p> + +<p>(<i>c.</i>) <i>Successive Stages of Volcanic Action in Auvergne.</i>—The +volcanic region here described, which has an +area of about one hundred square miles, does not +appear to have been at one and the same period of +time the theatre of volcanic action over its whole +extent. On the contrary, this action appears to have +commenced at the southern border of the region in +the Cantal, and travelling northwards, to have broken +out in the Mont Dore region; finally terminating its +outward manifestations among the craters and domes +of the Puy de Dôme. In a similar manner the volcanic +eruptions of the Haute Loire and Ardèche, +lying to the eastward, and separated from those of the +Cantal by the granitoid ridge of the Montagnes de +Margeride, belong to two successive periods referable +very closely to those of the Mont Dore and the Puy de +<span class="pagenum"><a name="Page_98" id="Page_98">[Pg 98]</a></span>Dôme groups.<a name="FNanchor_5_83" id="FNanchor_5_83"></a><a href="#Footnote_5_83" class="fnanchor">[5]</a> The evidence in support of this view +is very clear and conclusive; for, while the volcanic +craters formed of ash, lapilli, and scoriæ, together with +the rounded domes of trachytic rock of which the +Puy de Dôme group is composed, preserve the +form and surface indications of recently extinguished +volcanoes, those which we may assume to have been +piled up in the region of Mont Dore and Cantal have +been entirely swept away by prolonged rain and river +action, and the sites of the ancient craters and cones +of eruption are only to be determined by tracing the +great sheets of lava up the sides of the valleys to their +sources, generally situated at the culminating points +of their respective groups. Other points of evidence +of the great antiquity of the latter groups might be +adduced from the extent of the erosion which has +taken place in the sheets of lava having their sources +in the vents of the Plomb du Cantal and of Mont Dore, +owing to which, magnificent valleys, many miles in +length and hundreds of feet in depth, have been cut +out of these sheets of lava and their supporting +rocks, whether granitic or lacustrine, and the materials +carried away by the streams which flow along their +beds. These points will be better understood when +I come to give an account of the several groups; +and in doing so I will commence with that of the +Cantal.<a name="FNanchor_6_84" id="FNanchor_6_84"></a><a href="#Footnote_6_84" class="fnanchor">[6]</a></p> + +<p>(<i>d.</i>) <i>The Volcanoes of the Cantal.</i>—The original +<span class="pagenum"><a name="Page_99" id="Page_99">[Pg 99]</a></span>crater-cones of this group have entirely disappeared +throughout the long ages which have elapsed since the +lava-streams issued forth from their internal reservoirs. +The general figure of this group of volcanic mountains +is that of a depressed cone, whose sides slope away in +all directions from the central heights, which are +deeply eroded by streams rising near the apex and +flowing downwards in all directions towards the +circumference of the mountain, where they enter the +Lot, the Dordogne, and the Allier. The orifice of +eruption was situated at the Plomb du Cantal, formed +of solid masses of trachyte, which, owing, as Mr. +Scrope supposes, to a high degree of fluidity, were +able to extend to great distances in extensive sheets, +and were afterwards covered by repeated and widely-spread +flows of basalt; so that the trachyte towards +the margin of the volcanic area becomes less conspicuous +than the basalt by which it is more or +less concealed from view, or overlapped. Extensive +beds of tuff and breccia accompany the trachytic +masses.</p> + +<p>Magnificent sections of the rocks are laid open to +view along the sides of the valleys, which are steep +and rock-bound. Except towards the south-west, +about Aurillac, where lacustrine strata overlie the +granite, the platform from which rises the volcanic +dome is composed of granitic or gneissose rocks. +Accompanying the lava-streams are great beds of +volcanic agglomerate, which Mr. Scrope considers to +have been formed contemporaneously with the lava +which they envelop, and to be due to torrents of +water tumultuously descending the sides of the +volcano at periods of eruption, and bearing down +immense volumes of its fragmental <i>ejecta</i> in company +<span class="pagenum"><a name="Page_100" id="Page_100">[Pg 100]</a></span>with its lava-streams.<a name="FNanchor_7_85" id="FNanchor_7_85"></a><a href="#Footnote_7_85" class="fnanchor">[7]</a> Nowhere throughout +this region do beds of trachyte and basalt alternate +with one another; in all cases the basalt is the newer +of the two varieties of rock, and this is generally the +case throughout the region here described.</p> + +<p>(<i>e.</i>) <i>Volcanoes of Mont Dore.</i>—This mountain lies to +the north of that of Cantal, and somewhat resembles +it in general structure and configuration. Like +Cantal, it is destitute of any distinct crater; all that is +left of the central focus of eruption being the solidified +matter which filled the throat of the original volcano, +and which forms a rocky mass of lava, rising in its +highest point, the Pic de Saucy, to an elevation (as +given by Ramond) of 6258 feet above the level of the +sea, thus exceeding that of the Plomb du Cantal by +128 feet. Its figure will be best understood by +supposing seven or eight rocky summits grouped +together within a circle of about a mile in diameter, +from whence, as from the apex of an irregular and +flattened cone, all the sides slope more or less +rapidly downwards, until their inclination is gradually +lost in the plain around. This dome-shaped +mass has been deeply eroded on opposite sides +by the valleys of the Dordogne and Chambon; +while it is further furrowed by numerous minor +streams.<a name="FNanchor_8_86" id="FNanchor_8_86"></a><a href="#Footnote_8_86" class="fnanchor">[8]</a></p> + +<p>The great beds of volcanic rock, disposed as above +stated, consist of prodigious layers of scoriæ, pumice-stones, +and detritus, alternating with beds of trachyte +and basalt, which often descend in uninterrupted currents +till they reach the granite platform, and then +spread themselves for miles around. The sheets of +basalt are found to stretch to greater distances than +<span class="pagenum"><a name="Page_101" id="Page_101">[Pg 101]</a></span>those of trachyte, and have flowed as far as 15 or +20 miles from their orifices of eruption; while in +some cases, on the east and north sides, they have extended +as far as 25 or 30 miles from the central height. +On the other hand, a radius of about ten miles from +the centre would probably include all the streams of +trachyte;—so much greater has been the viscosity of +the basalt over the latter rock. Some portions of these +great sheets of lava, cut off by river valleys or eroded +areas from the main mass of which they once +formed a part, are found forming isolated terraces and +plateaux either on the granitic platform, or resting on +the fresh-water strata of the valley of the Allier, while +in a northern direction they overspread a large portion +of the granitic plateau from which rise the Puy de +Dôme and associated volcanic mountains. Still more +remarkable are the cases in which these lava-streams +have descended into the old river channels which +drained the granitic plateau. Thus the current which +took its origin in the Puy Gros descended into the +valley of the Dordogne, while another stream invaded +the gorge of Champeix on the eastern side.</p> + +<p>The more ancient lava-streams just described are +invaded by currents and surmounted by cones of +eruption of more recent date, similar to those of the +Puy de Dôme group lying to the northward. Such +cones and currents, amongst which are the Puy de +Tartaret and that of Montenard, present exactly the +same characters as those of this group, to which we +shall return further on.</p> + +<p>(<i>f.</i>) <i>Volcanoes of the Haute Loire and Ardèche.</i>—Separated +by the valley of the Allier and the granitic +ridge of La Margeride from the volcanic regions of +Cantal and Mont Dore is another volcanic region of +<span class="pagenum"><a name="Page_102" id="Page_102">[Pg 102]</a></span>great extent, which reaches its highest elevation in the +central points of Mont Mezen, attaining an elevation +(according to Cordier) of 5820 feet, and formed of +"clinkstone." The volcanic products of Mezen have +been erupted from one central orifice of vast size, and +consist mainly of extensive sheets of "clinkstone," +a variety of trachytic lava, which have taken courses +mainly towards the north-west and south-east. These +great sheets, one of which appears to have covered +a space more than 26 miles in length with an average +breadth of 6 miles, thus overspreading an estimated +area of 156 square miles, has been deeply eroded by +streams draining into the Loire, along whose banks +the rocks tower in lofty cliffs; while it has also suffered +enormous denudation, by which outlying fragments +are disconnected from the main mass, and form flat-topped +hills and plateaux as far distant as Roche en +Reigner and Beauzac, at the extreme distance (as +stated above) of 26 miles from the source of +eruption.</p> + +<p>But even more remarkable than the above are the +vast basaltic sheets which stretch away for a distance +of 30 miles by Privas almost to the banks of the +Rhône, opposite Montlimart. These have their origin +amongst the clinkstone heights of Mont Mezen, and +taking their course along the granitic plateau in a +south-easterly direction, ultimately pass over on to +the Jurassic and Cretaceous formations composing the +plateau of the Coiron, which break off in vertical cliffs +from 300 to 400 feet in height, surmounting the +slopes that rise from the banks of the Ardèche and +Escourtais rivers near Villeneuve de Bere. This is +probably one of the most extensive sheets of basalt +with which we are acquainted in the European area, +<span class="pagenum"><a name="Page_103" id="Page_103">[Pg 103]</a></span>and it is only a remnant of a vastly greater original +sheet.<a name="FNanchor_9_87" id="FNanchor_9_87"></a><a href="#Footnote_9_87" class="fnanchor">[9]</a></p> + +<div class="figcenter"> +<a name="FIGURE_19"></a> +<a href="images/figure19full.jpg"> + <img src="images/figure19.jpg" alt="Mont Demise" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 19.</span>—Mont Demise, near Le Puy, seen from the S.E. (After Scrope.)—1. Building standing on old breccia, rocks of +the Col; 2. Road to Brioude; 3. Croix de la Paille; 4. Orgue d'Expailly (basalt); 5. Spot where human bones were found. +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_104" id="Page_104">[Pg 104]</a></span></p><p>(<i>g.</i>) <i>Newer Volcanoes of the Haute Loire (the Velay +and Vivarais).</i>—Subsequently to the formation of the +lava-streams above described, and probably after the +lapse of a lengthened period, the region of the Haute +Loire and Ardèche became the scene of a fresh outburst +of volcanic action, during which the surface of +the older lavas, or of the fundamental granite, was +covered by numerous crater-cones and lava-streams +strewn along the banks of the Allier and of the Loire +for many miles. These cones and craters are not +quite so fresh as those of the Mont Dôme group; +those of the Haute Loire being slightly earlier in +point of time, and, as Daubeny shows, belonging +to a different system. So numerous are these more +recent cones and craters that Scrope counted more +than 150 of them, and probably omitted many.</p> + +<p>The volcanic phenomena now described have a +special interest as bearing on the question whether +man was an inhabitant of this region at the time of +these later eruptions. The question seems to be +answered in the affirmative by the discovery of a +human skull and several bones in the volcanic breccia +of Mont Demise, in company with remains of the +elephant (<i>E. primigenius</i>), rhinoceros (<i>R. tichorhinus</i>), +stag, and other large mammifers. The discovery of +these remains was made in the year 1844, and the +circumstances were fully investigated and reported +upon by M. Aymard, and afterwards by Mr. Poulett +Scrope, upon whose mind no possible doubt of the +<span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span>fact remained. From what we now know of the +occurrence of human remains and works of art in +other parts of France and Europe, no surprise need +be felt at the occurrence of human remains in company +with some extinct mammalia in these volcanic +tuffs, which belong to the Post-Pliocene or superficial +alluvia antecedent to the historic period.<a name="FNanchor_10_88" id="FNanchor_10_88"></a><a href="#Footnote_10_88" class="fnanchor">[10]</a></p> + +<p>(<i>h.</i>) <i>Mont Dôme Chain.</i>—We now come to the +consideration of the most recent of all the volcanic +mountain groups of the region of Central France, that +of the Puy de Dôme, lying to the north of Mont Dore +and Cantal. We have seen that there is almost conclusive +evidence that man was a witness to the later +volcanic outbursts of the Vivarais, and as these craters +seem to be of somewhat earlier date than those of the +Puy de Dôme group, we cannot doubt that they were +in active eruption when human beings inhabited the +country, and not improbably within what is known +as the <i>Historic Period</i>. No mention, however, is made +either by Cæsar, Pliny, or other Roman writers of the +existence of active volcanoes in this region. Cæsar, +who was a close observer, and who carried the Roman +arms into Auvergne, makes no mention of such; nor +yet does the elder Pliny, who enumerated the known +burning mountains of his day all over the Roman +<span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span>Empire. It is not till we come down to the fifth +century of our era that we find any notices which +might lead us to infer the existence of volcanic action +in Central France. This is the well-known letter +written by Sidonius Apollonarius, bishop of Auvergne, +to Alcinus Avitus, bishop of Vienne, in which the +former refers to certain terrific terrestrial manifestations +which had occurred in the diocese of the latter. +But, as Dr. Daubeny observes, this is no evidence of +volcanic action in Auvergne, where Sidonius himself +resided; the terrestrial disturbances above referred +to may have been earthquake shocks of extreme +severity.<a name="FNanchor_11_89" id="FNanchor_11_89"></a><a href="#Footnote_11_89" class="fnanchor">[11]</a></p> + +<p>But although we have no reliably historical record +of volcanic action amongst the mountains of the Mont +Dôme group, the fact that these are, comparatively, +extremely recent will be evident to an observer visiting +this district, and this conclusion is based on three +principal grounds: first, because of the well-preserved +forms of the original craters, though generally composed +of very loose material, such as ashes, lapilli, and +slag; secondly, because of the freshness of the lava-streams +over whose rugged surfaces even a scanty +herbage has in some places scarcely found a footing;<a name="FNanchor_12_90" id="FNanchor_12_90"></a><a href="#Footnote_12_90" class="fnanchor">[12]</a> +and thirdly, because the lava from the crater-cones has +invaded channels previously occupied by the earlier +lavas, or those which had been eroded since the +overflow of the great basaltic sheets of Mont Dore. +Still, as in the case of the valleys of Lake Aidot, of +Channonat, and of Royat, these streams are sufficiently +<span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span>ancient to have given time for the existing rivers to +have worn out in them channels of some depth, but +bearing no comparison to the great valleys which had +been eroded out of the more ancient lavas, such as +those of the Coiron, of the Ardèche, and of the +Dordogne and Chambon in the district of Mont Dore.</p> + +<p>(<i>i.</i>) <i>Dome-shaped Volcanic Hills.</i>—I have previously +(<a href="#Page_15">page 15</a>) referred to the two classes of volcanic eminences +to be found in the chain of the Puy de Dôme; +one indicated by the name itself, formed of a variety +of trachytic lava called "domite," and of the form of a +dome; the other, composed of fragmental matter piled +up in the form of a crater or cup, often ruptured on +one side by a stream of lava which has burst through +the side, owing to its superior density. Of the former +class the Puy de Dôme and the Grand Sarcoui (see +<a href="#FIGURE_18">Fig. 18</a>) are the most striking examples out of the +five enumerated by Scrope, while there is a large +number, altogether sixty-one, belonging to the latter +class. These domes and crater-cones, as already +stated, rise from a platform of granite, either directly +or from one formed of the lava-sheets of the Mont +Dore region, which in turn overlies the granitic platform. +Of the nearly perfect craters there are the +Petit Puy de Dôme, lying partially against the +northern flank of the greater eminence; the Puy de +Cone, remarkable for the symmetry of its conical +form, rising to a height of 900 feet from the plain; +and the Puys de Chaumont and Thiolet lying to the +north of the Puy de Dôme. Of those to the south of +this mount, two out of the three craters of the Puy de +Barme and the Puy de Vichatel are perfect; but most +of the crater-cones south of the Puy de Dôme are +breached. Some of the lava streams by which these +<span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span>craters were broken down flowed for long distances. +That the lava followed the showers of ashes and lapilli +forming the walls of the craters is rendered very evident +in the case of the Puy de la Vache, whose lava-stream +coalescing with those from the Puy de la Solas and +Puy Noir, deluged the surrounding tracts and flowed +down the Channonat Valley as far as La Roche +Blanc in the Vale of Clermont. In the interior of +the upper part of the crater still remaining may be +seen the level (so to speak) to which the molten lava +rose before it burst its barrier. This level is marked +by a projecting platform of reddish or yellow material, +rich in specular iron, apparently part of the frothy +scum which formed on the surface of the lava and +adhered to the side of the basin at the moment of its +being emptied.</p> + +<p>Space does not permit a fuller description of this +remarkable assemblage of extinct volcanoes, and the +reader must be referred for further details to the work +of Mr. Scrope. I shall content myself with some +further reference to the central figure in this grand +chain, the Puy de Dôme itself.</p> + +<p><i>Ascent of the Puy de Dôme.</i>—On ascending by the +winding path up the steep side of the mount, and on +reaching the somewhat flattened summit, the first +objects which strike the eye are the massive foundations +of the Roman temple of Mercury; they are hewn +out of solid grey lava, altogether different from the +rock of the Puy de Dôme itself, which must have been +obtained from one of the lava-sheets of the Mont +Dore group. To have carried these large blocks to +their present resting-place must have cost no little +labour and effort. The temple is supposed to have +been surmounted by a colossal statue of the winged +<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span>deity, visible from all parts of the surrounding +country which was dedicated to his honour, and the +foundations were only discovered a few years ago +when excavating for the foundation of the observatory, +which stands a little further on under the charge +of Professor Janssen. On proceeding to the northern +crest of the platform a wonderful view of the extinct +craters and domes—about forty in number, and terminating +in the Puy de Beauny, the most northerly +member of the chain—is presented to the spectator. +To the right is the Vale of Clermont and the rich valley +of the Allier merging into the great plain of Central +France. On the south side of the platform a no less +remarkable spectacle meets the eye. The chain of +Puys and broken craters stretches away southwards +for a distance of nearly ten miles, while the horizon is +bounded in that direction by the lofty masses of the +Mont Dore, Cantal, and Le Puy ranges. Nor does +it require much effort of the imagination to restore +the character of the region when these now dormant +volcanoes were in full activity, projecting showers of +ashes and stones high into the air amidst flames of +fire and vast clouds of incandescent gas and steam.</p> + +<p>The material of which the Puy de Dôme is formed +consists of a light grey, nearly white, soft felsitic +lava, containing crystals of mica, hornblende, and +specular iron-ore. It is highly vesicular, and was +probably extruded in a pasty condition from a throat +piercing the granitic plateau and the overlying sheet +of ancient lava of Mont Dore. It has been suggested +that such highly felsitic and acid lavas as that of +which the Puy de Dôme, the Grand Sarcoui, and +Cliersou are composed, may have had their origin +in the granite itself, melted and rendered viscous by +<span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span>intense heat. Dr. E. Gordon Hull has suggested +that the domite hills (owing to their low specific +gravity) may have filled up pre-existing craters +of ashes and scoriæ without rupturing them, as +in the case of the heavier basaltic lavas, and then +still continuing to be extruded, may have entirely +enveloped them in its mass; so that each domite +hill encloses within its interior a crater formed of +ashes, stones, and scoriæ. In the case of the Puy +de Dôme there is some evidence that the domite +matter rests on a basis of ashes and scoriæ, which +may be seen in a few places around the base of the +cone. It is difficult without some such theory as +this to explain how a viscous mass was able to +raise mountains some 2000 or 3000 feet above the +surrounding plain.<a name="FNanchor_13_91" id="FNanchor_13_91"></a><a href="#Footnote_13_91" class="fnanchor">[13]</a></p> + +<p>(<i>j.</i>) <i>Sketch of the Volcanic History of Central +France.</i>—It now only remains to give a brief <i>resumé</i> +of the volcanic history of this region as it may be +gathered from the relations of the rocks and strata +to the volcanic products, and of these latter to each +other.</p> + +<p><i>1st Stage.</i>—It would appear that at the close of +the Eocene period great terrestrial changes occurred. +The bed of the sea was converted into dry land, the +strata were flexured and denuded, and a depression +was formed in the granitic floor of Central France, +which, in the succeeding Miocene period, was converted +into an extensive lake peopled by molluscs, +fishes, reptiles, and pachyderms of the period.</p> + +<p><span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span></p><p><i>2nd Stage.</i>—Towards the close of the Miocene +epoch volcanic eruptions commenced on a grand +scale over the granitic platform in the districts now +called Mont Dore, Cantal, and the Vivarais. Vast +sheets of trachytic and basaltic lavas successively +invaded the tracts surrounding the central orifices of +eruption, now constituting the more ancient of the +lava-sheets of the Auvergne region, and, invading +the waters of the neighbouring lake, overspread the +lacustrine deposits which were being accumulated +therein. These volcanic eruptions probably continued +throughout the Pliocene period, interrupted +by occasional intervals of inactivity, and ultimately +altogether ceased.</p> + +<p><i>3rd Stage.</i>—Towards the close of the Pliocene +period terrestrial movements took place, owing to +which the waters of the lake began to fall away, and +the sheets of lava were subjected to great denudation. +This process, probably accelerated by excessive rainfall +during the succeeding Post-Pliocene and Pluvial +periods, was continued until plains and extensive +river-valleys were eroded out of the sheets of lava and +their supporting granitic rocks and the adjoining +lacustrine strata.</p> + +<p><i>4th Stage.</i>—A new outburst of volcanic forces +marks this stage, during which the chain of the Puy +de Dôme was thrown up on the west, and that of the +newer cones of the Vivarais on the south-east of the +lacustrine tract. The waters of the lake were now +completely drained away through the channel of the +Allier, and denudation, extending down to the +present day, began over the area now forming the +Vale of Clermont and adjoining districts. The volcanic +action ultimately spent its force; and somewhere +<span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span>about the time of the appearance of man, the mammoth, +rhinoceros, stag, and reindeer on the scene, +eruptions entirely ceased, and gradually the region +assumed those conditions of repose by which it is +now physically characterised.</p> + +<div class="footnote"><p><a name="Footnote_1_79" id="Footnote_1_79"></a><a href="#FNanchor_1_79"><span class="label">[1]</span></a> The literature referring to this region is very extensive. Guettard +in 1775, afterwards Faujas, published descriptions of the rocks of the +Vivarais and Velay; and Desmarest's geological map, published in +1779, is a work of great merit. The district was afterwards described +by Daubeny, Lyell, Von Buch, and others; but by far the most +complete work is that of Scrope, entitled <i>Volcanoes of Central France</i>, +containing maps and numerous illustrations, published in 1826, and +republished in a more extended form in 1858; to this I am largely +indebted.</p></div> + +<div class="footnote"><p><a name="Footnote_2_80" id="Footnote_2_80"></a><a href="#FNanchor_2_80"><span class="label">[2]</span></a> A monument to Pascal, erected by the citizens, occupies the centre +of the square in Clermont. It will be remembered that Pascal verified +the conclusions arrived at by Torricelli regarding the pressure of the +atmosphere, by carrying a Torricellian tube to the summit of the +Puy de Dôme, and recording how the mercury continually fell during +the ascent, and rose as he descended. This experiment was made in +1645.</p></div> + +<div class="footnote"><p><a name="Footnote_3_81" id="Footnote_3_81"></a><a href="#FNanchor_3_81"><span class="label">[3]</span></a> In this visit to Auvergne in the summer of 1880, the author was +accompanied by his son, Dr. E. Gordon Hull, and Sir Robert S. Ball. +On reaching the station at the summit of the ridge it seemed as if +the volcanic fires had again been lighted, for the whole sky was aglow +with the rays of the western sun.</p></div> + +<div class="footnote"><p><a name="Footnote_4_82" id="Footnote_4_82"></a><a href="#FNanchor_4_82"><span class="label">[4]</span></a> On the other hand, certain beds of ash and other volcanic <i>ejecta</i> +occur in <i>the uppermost</i> strata of lake deposits of Limagne, so that these +may indicate the commencement of the period of eruption, as suggested +further on.</p></div> + +<div class="footnote"><p><a name="Footnote_5_83" id="Footnote_5_83"></a><a href="#FNanchor_5_83"><span class="label">[5]</span></a> Only very closely; for Mr. Scrope considers that the crater-cones +of the chain of the Haute Loire give evidence of a somewhat earlier +epoch of activity than those of the Puy de Dôme, as they have undergone +a greater amount of subaerial erosion.</p></div> + +<div class="footnote"><p><a name="Footnote_6_84" id="Footnote_6_84"></a><a href="#FNanchor_6_84"><span class="label">[6]</span></a> The extent of this river erosion has been clearly brought out by +Scrope, and is admirably illustrated by several of his panoramic views, +such as that in Plate IX. of his work.</p></div> + +<div class="footnote"><p><a name="Footnote_7_85" id="Footnote_7_85"></a><a href="#FNanchor_7_85"><span class="label">[7]</span></a> Scrope, <i>loc. cit.</i>, p. 147.</p></div> + +<div class="footnote"><p><a name="Footnote_8_86" id="Footnote_8_86"></a><a href="#FNanchor_8_86"><span class="label">[8]</span></a> Scrope, <i>loc. cit.</i>, p. 144.</p></div> + +<div class="footnote"><p><a name="Footnote_9_87" id="Footnote_9_87"></a><a href="#FNanchor_9_87"><span class="label">[9]</span></a> Scrope gives a view of these remarkable basaltic cliffs in Plate +XII. of his work, from which the above account is taken. At one spot +near the village of Le Gua there is a break in the continuity of the sheet.</p></div> + +<div class="footnote"><p><a name="Footnote_10_88" id="Footnote_10_88"></a><a href="#FNanchor_10_88"><span class="label">[10]</span></a> See Scrope, <i>loc. cit.</i>, p. 181; also Appendix, <a href="#Page_228">p. 228</a>. While there +is no <i>primâ facie</i> reason for questioning the origin of the Demise skull, +yet from what Lyell states in his <i>Antiquity of Man</i>, p. 196, it will be +seen that he found it impossible to identify its position, or to determine +beyond question that its interment was due to natural causes. But +assuming this to be the case, he shows how the individual to whom it +belonged might have been enveloped in volcanic tuff or mud showered +down during the final eruption of the volcano of Demise. MM. +Hébert and Lartet, on visiting the locality, also failed to find <i>in situ</i> any +exact counterpart of the stone now in the museum of Le Puy.</p></div> + +<div class="footnote"><p><a name="Footnote_11_89" id="Footnote_11_89"></a><a href="#FNanchor_11_89"><span class="label">[11]</span></a> See Daubeny, <i>Volcanoes</i>, p. 31.</p></div> + +<div class="footnote"><p><a name="Footnote_12_90" id="Footnote_12_90"></a><a href="#FNanchor_12_90"><span class="label">[12]</span></a> That is to say, the surfaces of the lava-streams are not at all, or +only slightly, decomposed into soil suitable for the growth of plants, +except in rare instances.</p></div> + +<div class="footnote"><p><a name="Footnote_13_91" id="Footnote_13_91"></a><a href="#FNanchor_13_91"><span class="label">[13]</span></a> E. G. Hull, "On the Domite Mountains of Central France," +<i>Scien. Proc. Roy. Dublin Society</i>, July 1881, p. 145. Dr. Hull determined +the density of the domite of the Puy de Dôme to be 2.5, while +that of lava is about 3.0.</p></div> +<p><span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_II_CHAPTER_VII" id="PART_II_CHAPTER_VII"></a>CHAPTER VII. +<br /><br /> +THE VOLCANIC DISTRICT OF THE RHINE VALLEY.</h2> + + +<p>The region bordering the Rhine along both its +banks above Bonn, and extending thence along the +valley of the Moselle and into the Eifel, has been +the theatre of active volcanic phenomena down into +recent times, but at the present day the volcanoes are +dormant or extinct.</p> + +<p>(<i>a.</i>) <i>Geological Structure.</i>—The fundamental rocks +of this region belong to the Silurian, Devonian, and +Carboniferous systems, consisting of schists, grits, and +limestones, with occasional horizontal beds of Miocene +sandstone and shale with lignite, resting on the +upturned edges of the older rocks. Scattered over +the greater part of the district here referred to are a +number of conical eminences, often with craters, the +bottoms of which are usually sunk much below the +present level of the country, and thus receiving the +surface drainage, have been converted into little +lakes called "maars," differing from ordinary lakes by +their circular form and the absence of any <i>apparent</i> +outlet for their waters.<a name="FNanchor_1_92" id="FNanchor_1_92"></a><a href="#Footnote_1_92" class="fnanchor">[1]</a></p> + +<p><span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span></p><p>But before entering into details, it may be desirable +to present the reader with a short outline of the +physical history of the region (which has been +ably done by Dr. Hibbert in his treatise, to which I +have already referred), so as to enable him better to +understand the succession of physical events in its +volcanic history.</p> + +<div class="figcenter"> +<a name="FIGURE_20"> + <img src="images/figure20.jpg" alt="Rhenish area" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 20.</span>—Sketch Map to show the physical condition of the Rhenish +area in the Miocene epoch.—(After Hibbert.) +</td></tr> +</table> +</div> + +<p>(<i>b.</i>) <i>Physical History.</i>—From the wide distribution +of stratified deposits of sand and clay at high levels +on both banks of the Rhine north of the Moselle, +it would appear that an extensive fresh-water basin, +which Dr. Hibbert calls "The Basin of Neuwied," +occupied a considerable tract on both banks, in the +centre of which the present city of Neuwied stands. +This basin was bounded towards the south by the +slopes of the Hündsruck and Taunus, which at the +<span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span>time here referred to formed a continuous chain of +mountains. (<a href="#FIGURE_20">Fig. 20</a>.) To the south of this chain +lay the Tertiary basin of Mayence, which was connected +at an early period—that of the Miocene—with +the waters of the ocean, as shown by the fact that the +lower strata contain marine shells; these afterwards +gave place to fresh-water conditions. The basin of +Neuwied was bounded towards the north by a ridge of +Devonian strata which extended across the present +gorge of the Rhine between Andernach and Linz, +and to the north of this barrier lay another more +extensive fresh-water basin, that of Cologne. From +this it will be seen that the Rhine, as we now find +it, had then only an infantile existence; in fact, its +waters to the south of the Hündsruck ridge drained +away towards the south. But towards the commencement +of the Pliocene period the barriers of the +Hündsruck and Taunus, as also that of the Linz, were +broken through, and the course of the waters was +changed; and thus gradually, as the river deepened its +bed, the waters were drained off from the great lakes.<a name="FNanchor_2_93" id="FNanchor_2_93"></a><a href="#Footnote_2_93" class="fnanchor">[2]</a> +This rupture of the barriers may have been due, +in the first instance, to the terrestrial disturbances +accompanying the volcanic eruptions of the Eifel and +Siebengebirge, though the erosion of the gorges at +Bingen and at Linz to their present depth and +dimensions is of course due to prolonged river action. +It was about the epoch we have now arrived at—viz., +the close of the Miocene—that volcanic action +burst forth in the region of the Lower Rhine. It is +probable that this action commenced in the district +<span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span>of the Siebengebirge, and afterwards extended into +that of the Moselle and the Eifel, the volcanoes of +which bear evidence of recent date. Layers of trachytic +tuff are interstratified with the deposits of sand, clay, +and lignite of the formation known as that of the +Brown Coal—of Miocene age—which underlies nearly +the whole of the volcanic district on both sides of the +Rhine near Bonn,<a name="FNanchor_3_94" id="FNanchor_3_94"></a><a href="#Footnote_3_94" class="fnanchor">[3]</a> thus showing that volcanic action +had already commenced in that part to some extent; +but it does not appear from Dr. Hibbert's statement +that any such fragments of eruptive rock are to be +found in the strata which were deposited over the +floor of the Neuwied basin.<a name="FNanchor_4_95" id="FNanchor_4_95"></a><a href="#Footnote_4_95" class="fnanchor">[4]</a> It will be recollected +that the epoch assigned for the earliest volcanic eruptions +of Auvergne was that here inferred for those of the +Lower Rhine—viz., the close of the Miocene stage—and +from evidence subsequently to be adduced from +other European districts, it will be found that there +was a very widely spread outburst of volcanic action +at this epoch.</p> + +<p>(<i>c.</i>) <i>The Range of the Siebengebirge.</i>—This range +of hills—formed of the older volcanic rocks of the +Lower Rhine—rises along the right bank of this +noble river opposite Bonn, where it leaves the narrow +gorge which it traverses all the way from Bingen, and +opens out on the broad plain of Northern Germany. +The range consists of a succession of conical hills sometimes +flat-topped—as in the case of Petersberg; and at +the Drachenfels, near the centre of the range it presents +to the river a bold front of precipitous cliffs of trachyte +<span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span>porphyry. The sketch (<a href="#FIGURE_21">Fig. 21</a>) here presented was +taken by the author in 1857 from the old extinct volcano +of Roderberg, and will convey, perhaps, a better +idea of the character of this picturesque range than a +description. The Siebengebirge, although appearing +as an isolated group of hills, is in reality an offshoot +from the range of the Westerwald, which is connected +with another volcanic district of Central +Germany known as the Vogelsgebirge. The highest +point in the range is attained in the Lohrberg, which +rises 1355 feet above the sea; the next, the Great +Tränkeberg, 1330 feet; and the next, Great Oelberg, +1296 feet.</p> + +<div class="figcenter"> +<a name="FIGURE_21"> + <img src="images/figure21.jpg" alt="Range of the Siebengebirge" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 21.</span>—The Volcanic Range of the Siebengebirge, seen from the left bank of the Rhine, above Bonn.—(Original.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span></p><p>The range consists mainly of trachytic rocks—namely, +trachyte-conglomerate, and solid trachyte, +of which H. von Dechen makes two varieties—that +of the Drachenfels, and that of the Wolkenburg. But +associated with these highly-silicated varieties of lava—and +generally, if not always, of later date—are basaltic +rocks which cap the hills of Petersberg, Nonnenstrom, +Gr. and Ll. Oelberg, Gr. Weilberg, and Ober +Dollendorfer Hardt. The question whether there is a +transition from the one variety of volcanic rock into +the other, or whether each belongs to a distinct and +separate epoch of eruption, does not seem to be very +clearly determined. Mr. Leonard Horner states that +it would be easy to form a suite of specimens showing +a gradation from a white trachyte to a black basalt;<a name="FNanchor_5_96" id="FNanchor_5_96"></a><a href="#Footnote_5_96" class="fnanchor">[5]</a> +but we must recollect that when Mr. Horner wrote, +the microscopic examination of rocks by means of +thin sections was not known or practised, and an +examination by this process might have proved that +this apparent transition is unreal. According to H. +<span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span>von Dechen, there are sheets of basalt older than the +greater mass of the brown coal formation, and others +newer than the trachyte;<a name="FNanchor_6_97" id="FNanchor_6_97"></a><a href="#Footnote_6_97" class="fnanchor">[6]</a> while dykes of basalt +traversing the trachytic lavas are not uncommon.<a name="FNanchor_7_98" id="FNanchor_7_98"></a><a href="#Footnote_7_98" class="fnanchor">[7]</a></p> + +<p>The trachyte-conglomerate—which seems to be +associated with the upper beds of the brown coal strata—is +traversed by dykes of trachyte of later date; and +though it is difficult to trace the line between the two +varieties of this rock on the ground, Dr. von Rath +has recognised the general distinction between them, +which consists in the greater abundance of hornblende +and mica in the trachyte of the Wolkenburg than in +that of the Drachenfels.</p> + +<p>The trachyte of the Drachenfels was probably the +neck of a volcano which burst through the fundamental +schists of the Devonian period. It is remarkable +for the large crystals of sanidine (glassy felspar) +which it contains, and has a rude columnar structure.</p> + +<p>The absence of any clearly-defined craters of +eruption, such as are to be found in the Eifel district +and on the left bank of the Rhine—as, for example, +in the case of the Roderberg—may be regarded as +sufficient evidence that this range is of comparatively +high antiquity. It seems to bear the same relation to +the more modern craters of the Eifel and Moselle that +the Mont Dore and Cantal volcanoes do to those of +the Puy de Dôme. In both cases, denudation carried +on throughout perhaps the Pliocene and Post-Pliocene +periods down to the present day has had the effect +of demolishing the original craters; so that what we +now observe as forming these ranges are the consolidated +<span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span>columns of original molten matter which +filled the throats of the old volcanoes, or the sheets of +lava which were extruded from them, but are now +probably much reduced in size and extent.</p> + +<p>Having thus given a description of the older +volcanic range on the right bank of the Rhine, we +shall cross the river in search of some details regarding +the more recent group of Rhenish volcanoes, commencing +with that of the Roderberg, a remarkable +hill a few miles south of Bonn, from which the view +of the Seven Mountains was taken.</p> + +<div class="figcenter"> +<a name="FIGURE_22"> + <img src="images/figure22.jpg" alt="Crater of the Roderberg" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 22.</span>—Section of the extinct crater of the Roderberg on the +bank of the Rhine, above Bonn.—(Original.) +</td></tr> +</table> +</div> + +<p>(<i>d.</i>) <i>The Roderberg.</i>—This crater, which was visited +by the author in 1857, is about one-fourth of a mile +in diameter, and is in the form of a cup with +gentle slopes on all sides. In its centre is a farmhouse +surrounded by corn-fields. The general section +through the hill is represented above (<a href="#FIGURE_22">Fig. 22</a>).</p> + +<p>The flanks on the north side are composed of loose +quartzose gravel (gerolle), a remnant of the deposits +formed around the margin of the "Basin of Neuwied" +described above (<a href="#Page_114">p. 114</a>). This gravel is found covering +the terraces of the brown coal formation several +hundred feet above the Rhine. Besides quartz-pebbles, +the deposit contains others of slate, grit, and +volcanic rock. On reaching the edge of the crater +we find the gravel covered over by black and purple +scoria or slag the superposition of the scoria on the +<span class="pagenum"><a name="Page_121" id="Page_121">[Pg 121]</a></span>gravel being visible in several places, showing that +the former is of more recent origin. On the opposite +side of the crater, overlooking the Rhine, we find the +cliff of Rolandsec composed of hard vesicular lava, +rudely prismatic, and extending from the summit of +the hill to its base, about 250 feet below. This is the +most northerly of the group of the Eifel volcanoes.</p> + +<p>(<i>e.</i>) <i>District of the Rivers Brühl and Nette.</i>—The +volcanic region of the Lower Eifel, drained by these +two principal streams which flow into the Rhine, will +amply repay exploration by the student of volcanic +phenomena, owing to the variety of forms and conditions +under which these present themselves within +a small space. The fundamental rock is slate or grit +of Devonian age, furrowed by numerous valleys, often +richly wooded, and diversified by conical hills of +trachyte; or by crater-cones, formed of basalt or ashes, +sometimes ruptured on one side, and occasionally sending +forth streams of lava, as in the cases of the Perlinkopf, +the Bausenberg, and the Engelerkopf. The +district attains its greatest altitude in the High Acht +(Der Hohe Acht), an isolated cone of slate capped +by basalt with olivine, and reaching a level of 2434 +Rhenish feet.<a name="FNanchor_8_99" id="FNanchor_8_99"></a><a href="#Footnote_8_99" class="fnanchor">[8]</a></p> + +<p>(<i>f.</i>) <i>The Laacher See.</i>—It would be impossible in +a work of this kind to attempt a detailed description +of the Eifel volcanoes, often of a very complex +character and obscure physical history, as in the case +of the basin of Rieden, where tufaceous deposits, +trachytic and basaltic lavas and crater-cones, are +confusedly intermingled, so that I shall confine my +<span class="pagenum"><a name="Page_122" id="Page_122">[Pg 122]</a></span>remarks to the deservedly famous district of the +Laacher See, which I had an opportunity of personally +visiting some years since.<a name="FNanchor_9_100" id="FNanchor_9_100"></a><a href="#Footnote_9_100" class="fnanchor">[9]</a></p> + +<div class="figcenter"> +<a name="FIGURE_23"> + <img src="images/figure23.jpg" alt="Laacher See" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 23.</span>—Plan and Section of the Laacher See, a lake on the +borders of the Eifel, occupying the crater of an old volcano.—G. Gravel +and volcanic sand forming banks of the lake and rim of old crater; +L. Sheet of trachytic lava with columnar structure; B. Basaltic dyke; +S. Devonian slate, etc. +</td></tr> +</table> +</div> + +<p>The Laacher See is a lake of an oval form, over +an English mile in the shorter diameter, and surrounded +by high banks of volcanic sand, gravel, and +scoriæ, except on the east side, where cliffs of clay-slate, +in a nearly vertical position, and striking nearly +E.W., may be observed. Its depth from the surface +of the water is 214 feet.<a name="FNanchor_10_101" id="FNanchor_10_101"></a><a href="#Footnote_10_101" class="fnanchor">[10]</a> The ashes of the encircling +<span class="pagenum"><a name="Page_123" id="Page_123">[Pg 123]</a></span>banks contain blocks of slate and lava which have +been torn from the sides of the orifice or neck of the +volcano and blown into the air; and there can be no +doubt that the ashes and volcanic gravel is the result +of very recent eruptions.</p> + +<p>At the east side of the lake we find a stream of +scoriaceous lava of a purple or reddish colour, highly +vesicular, and containing crystals of mica; but the +most important lava-stream is that which has taken +a southerly direction from the crater of the Laacher +See towards Nieder Mendig and Mayen, for a distance +of about six miles. This great stream is covered +throughout half its distance by beds of volcanic ash +and lapilli, but emerges into the air at a distance of +about two miles from the edge of the crater (see <a href="#FIGURE_23">Fig. +23</a>), and was formerly extensively quarried in underground +caverns for millstones. Here the rock is a +vesicular trachyte, of a greyish colour, solidified in +vertical columns of hexagonal form, about four feet in +diameter, and traversed by transverse joint planes. +These quarries have been worked from the time of the +Roman occupation of the country; and, before the +introduction of iron or steel rollers for grinding corn, +millstones were exported to all parts of Europe and +the British Isles from this quarry.<a name="FNanchor_11_102" id="FNanchor_11_102"></a><a href="#Footnote_11_102" class="fnanchor">[11]</a></p> + +<p>The district around the Laacher See is covered by +laminated <i>ejecta</i> of the old volcano, probably of subaërial +origin, through which bosses of the fundamental +slate peer up at intervals, while the surface is diversified +by several truncated cones.</p> + +<p>(<i>g.</i>) <i>Trass of the Brühl Valley.</i>—The Brühl Valley, +<span class="pagenum"><a name="Page_124" id="Page_124">[Pg 124]</a></span>which unites with that of the Rhine at the town of +that name, and drains the northern side of the volcanic +region, has always been regarded with much +interest by travellers for the presence of a deposit of +"trass" with which it is partially filled. The origin of +this valley was pre-volcanic, as it is hewn out of the +slaty rocks of the district. But at a later period it +became filled with volcanic mud (tuffstein), out of +which the stream has made for itself a fresh channel. +The source of this mud is considered by Hibbert<a name="FNanchor_12_103" id="FNanchor_12_103"></a><a href="#Footnote_12_103" class="fnanchor">[12]</a> +to have been the old volcano of the Lummerfeld, +which, after becoming dormant, was filled with water, +and thus became a lake. At a subsequent period, +however, a fresh eruption took place near the edge of +the lake, resulting in the remarkable ruptured crater +known as the Kunksköpfe, which rises about four +miles to the north of the Laacher See. The eruptions +of this volcano appear to have displaced the mud of +the Lummerfeld, causing it to flow down into the +deep gorge of the Brühl, which it completely filled, as +stated above.</p> + +<p>On walking down the valley one may sometimes +see the junction of the tuff with the slate-rock which +enfolds it. The tuff consists of white felspathic mud, +with fragments of slate and lava, reaching a depth in +some places of 150 feet. After it has been quarried +it is ground in mills, and used for cement stone under +the name of <i>trass</i>. It is said to resemble the volcanic +mud by which Herculaneum was overwhelmed during +the first eruption of Vesuvius, and which was produced +by the torrents of rain mixing with the ashes +as they were blown out of the volcano.</p> + +<p>Sufficient has probably now been written regarding +<span class="pagenum"><a name="Page_125" id="Page_125">[Pg 125]</a></span>the dormant, or recently extinct, volcanic districts of +Europe to give the reader a clear idea regarding +their nature and physical structure. Other districts +might be added, such as those of Central Germany, +Hungary, Transylvania, and Styria; but to do so +would be to exceed the proposed limits of this work; +and we may therefore pass on to the consideration +of the volcanic region of Syria and Palestine, +which adjoins the Mediterranean district we have +considered in a former page.</p> + +<div class="footnote"><p><a name="Footnote_1_92" id="Footnote_1_92"></a><a href="#FNanchor_1_92"><span class="label">[1]</span></a> Daubeny, <i>loc. cit.</i>, p. 71. The geology of this region has had +many investigators, of whom the chief are Steininger, <i>Erloschenen +Vulkane in der Eifel</i> (1820); Hibbert, <i>Extinct Volcanoes of the Basin +of Neuwied</i>, 1832; Nöggerath, <i>Das Gebirge im Rheinland</i>, etc., 4 vols.; +Horner, "On the Geology of Bonn," <i>Transactions of the Geological +Society, London</i>, vol. iv.</p></div> + +<div class="footnote"><p><a name="Footnote_2_93" id="Footnote_2_93"></a><a href="#FNanchor_2_93"><span class="label">[2]</span></a> The views of Dr. Hibbert are not inconsistent with those of the +late Sir A. Ramsay, on "The Physical History of the Valley of the +Rhine," <i>Quart. Jour. Geol. Soc.</i>, vol. xxx. (1874).</p></div> + +<div class="footnote"><p><a name="Footnote_3_94" id="Footnote_3_94"></a><a href="#FNanchor_3_94"><span class="label">[3]</span></a> Von Dechen, <i>Geog. Beschreib. des Siebengebirges am Rhein</i> +(Bonn, 1852).</p></div> + +<div class="footnote"><p><a name="Footnote_4_95" id="Footnote_4_95"></a><a href="#FNanchor_4_95"><span class="label">[4]</span></a> Hibbert, <i>loc. cit.</i>, p. 18.</p></div> + +<div class="footnote"><p><a name="Footnote_5_96" id="Footnote_5_96"></a><a href="#FNanchor_5_96"><span class="label">[5]</span></a> Horner, "Geology of Environs of Bonn," <i>Transactions of the +Geological Society</i>, vol. iv., new series.</p></div> + +<div class="footnote"><p><a name="Footnote_6_97" id="Footnote_6_97"></a><a href="#FNanchor_6_97"><span class="label">[6]</span></a> H. von Dechen, <i>Geog. Führer in das Siebengebirge am Rhein</i> +(Bonn, 1861).</p></div> + +<div class="footnote"><p><a name="Footnote_7_98" id="Footnote_7_98"></a><a href="#FNanchor_7_98"><span class="label">[7]</span></a> <i>Ibid.</i>, p. 191.</p></div> + +<div class="footnote"><p><a name="Footnote_8_99" id="Footnote_8_99"></a><a href="#FNanchor_8_99"><span class="label">[8]</span></a> Dr. Hibbert's work is illustrated by very carefully drawn and +accurate views of some of the old cones and craters of this district, +accompanied by detailed descriptions.</p></div> + +<div class="footnote"><p><a name="Footnote_9_100" id="Footnote_9_100"></a><a href="#FNanchor_9_100"><span class="label">[9]</span></a> The lava of Schorenberg, near Rieden, is interesting from the fact, +stated by Zirkel, that it contains leucite, nosean, and nephelin.—<i>Die +Mikros. Beschaf. d. Miner. u. Gesteine</i>, p. 154 (1873).</p></div> + +<div class="footnote"><p><a name="Footnote_10_101" id="Footnote_10_101"></a><a href="#FNanchor_10_101"><span class="label">[10]</span></a> Hibbert, <i>loc. cit.</i>, p. 23.</p></div> + +<div class="footnote"><p><a name="Footnote_11_102" id="Footnote_11_102"></a><a href="#FNanchor_11_102"><span class="label">[11]</span></a> At the time of the author's visit the underground caverns, which are +deliciously cool in summer, were used for the storage of the celebrated +beer brewed by the Moravians of Neuwied.</p></div> + +<div class="footnote"><p><a name="Footnote_12_103" id="Footnote_12_103"></a><a href="#FNanchor_12_103"><span class="label">[12]</span></a> Hibbert, <i>loc. cit.</i>, p. 129.</p></div> +<p><span class="pagenum"><a name="Page_126" id="Page_126">[Pg 126]</a></span></p> + + +<hr class="major" /> +<h1><a name="PART_III" id="PART_III"></a>PART III. +<br /><br /> +DORMANT OR MORIBUND VOLCANOES OF +OTHER PARTS OF THE WORLD.</h1> + + + +<hr class="major" /> +<h2><a name="PART_III_CHAPTER_I" id="PART_III_CHAPTER_I"></a>CHAPTER I. +<br /><br /> +DORMANT VOLCANOES OF PALESTINE AND ARABIA.</h2> + + +<p>(<i>a.</i>) <i>Region east of the Jordan and Dead Sea.</i>—The +remarkable line of country lying along the valley of +the Jordan, and extending into the great Arabian +Desert, has been the seat of extensive volcanic action +in prehistoric times. The specially volcanic region +seems to be bounded by the depression of the Jordan, +the Dead Sea, and the Arabah as far south as the Gulf +of Akabah; for, although Safed, lying at the head of +the Sea of Galilee on the west of the Jordan valley, is +built on a basaltic sheet, and is in proximity to an +extinct crater, its position is exceptional to the general +arrangement of the volcanic products which may be +traced at intervals from the base of Hermon into +Central Arabia, a distance of about 1000 miles.<a name="FNanchor_1_104" id="FNanchor_1_104"></a><a href="#Footnote_1_104" class="fnanchor">[1]</a></p> + +<p>The tract referred to has been described at intervals +<span class="pagenum"><a name="Page_127" id="Page_127">[Pg 127]</a></span>by several authors, of whom G. Schumacher,<a name="FNanchor_2_105" id="FNanchor_2_105"></a><a href="#Footnote_2_105" class="fnanchor">[2]</a> L. Lartet,<a name="FNanchor_3_106" id="FNanchor_3_106"></a><a href="#Footnote_3_106" class="fnanchor">[3]</a> +Canon Tristram,<a name="FNanchor_4_107" id="FNanchor_4_107"></a><a href="#Footnote_4_107" class="fnanchor">[4]</a> M. Niebuhr,<a name="FNanchor_5_108" id="FNanchor_5_108"></a><a href="#Footnote_5_108" class="fnanchor">[5]</a> and C. M. Doughty<a name="FNanchor_6_109" id="FNanchor_6_109"></a><a href="#Footnote_6_109" class="fnanchor">[6]</a> +may be specially mentioned in this connection.</p> + +<p>The most extensive manifestations of volcanic energy +throughout this long tract of country appear to be +concentrated at its extreme limits. At the northern +extremity the generally wild and rugged tract of the +Jaulân and Haurân, called in the Bible <i>Trachonitis</i>, +and still farther to the eastward the plateau of the +Lejah, with its row of volcanic peaks sloping down to +the vast level of Bashan, is covered throughout nearly +its whole extent by great sheets of basaltic lava, +above which rise at intervals, and in very perfect form, +the old crater-cones of eruption. A similar group of +extinct craters with lava-flows has been described and +figured by a recent traveller, Mr. C. M. Doughty, in +parts of Central Arabia. The general resemblance of +these Arabian volcanoes to those of the Jaulân is +unquestionable; and as they are connected with each +other by sheets of basaltic lava at intervals throughout +the land of Moab, it is tolerably certain that the +volcanoes lying at either end of the chain belong to +one system, and were contemporaneously in a state of +activity.</p> + +<p>(<i>b.</i>) <i>Geological Conditions.</i>—Before entering any +<span class="pagenum"><a name="Page_128" id="Page_128">[Pg 128]</a></span>further into particulars regarding the volcanic phenomena +of this region, it may be desirable to give a +short account of its geological structure, and the +physical conditions amongst which the igneous eruptions +were developed.</p> + +<p>Down to the close of the Eocene period the whole +region now under consideration was occupied by the +waters of the ocean. The mountains of Sinai were +islands in this ocean, which had a very wide range +over parts of Asia, Africa, and Europe. But at the +commencement of the succeeding Miocene stage the +crust was subjected to lateral contraction, owing to +which the ocean bed was upraised. The strata were +flexured, folded, and often faulted and fissured along +lines ranging north and south, the great fault of the +Jordan-Arabah valley being the most important. At +this period the mountains of the Lebanon, the table-lands +of Judæa and of Arabia, formed of limestone, +previously constituting the bed of the ocean during the +Eocene and Cretaceous periods, were converted into +land surfaces. Along with this upheaval of the sea-bed +there was extensive denudation and erosion of the +strata, so that valleys were eroded over the subaërial +tracts, and the Jordan-Arabah valley received its +primary form and outline.</p> + +<p>Up to this time there does not appear to have been +any outbreak of volcanic forces; but with the succeeding +Pliocene period these came into play, and eruptions +of basaltic lava took place along rents and +fissures in the strata, while craters and cones of slag, +scoriæ, and ashes were thrown up over the region +lying to the east of the Sea of Galilee and the sources +of the Jordan on the one hand, and the central parts +of the great Arabian Desert on the other. These +<span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span>eruptions, probably intermittent, continued into the +succeeding Glacial or Pluvial period, and only died +out about the time that the earliest inhabitants +appeared on the scene.</p> + +<p>(<i>c.</i>) <i>The Jaulân and Haurân.</i>—This tract is bounded +by the valley of the Jordan and the Sea of Galilee on +the west, from which it rises by steep and rocky +declivities into an elevated table-land, drained by the +Yarmûk (Hieromax), the Nahr er Rukkâd, and other +streams, which flow westwards into the Jordan along +deep channels in which the basaltic sheets and underlying +limestone strata are well laid open to view.</p> + +<p>On consideration it seems improbable that the great +sheets of augitic lava, such as cover the surface of +the land of Bashan, are altogether the product of the +volcanic mountains which appear to be confined to +special districts in this wide area. Some of the craters +do indeed send forth visible lava-streams, but they are +insignificant as compared with the general mass of +the plateau-basalts; and the crater-cones themselves +appear in some cases to be posterior to the platforms +of basalt from which they rise. It is very probable, +therefore, that the lavas of this region have, in the +main, been extruded from fissures of eruption at an +early period, and spread over the surface of the +country in the same manner as those of the Snake +River region, and the borders of the Pacific Ocean of +North America, and possibly of the Antrim Plateau +in Ireland, afterwards to be described.</p> + +<p>The volcanic hills which rise above the plateau are +described in detail by Schumacher. Of these, Tell +Abû Nedîr is the largest in the Jaulân. It reaches an +elevation of 4132 feet above the Mediterranean Sea, +and 1710 feet above the plain from which it rises; +<span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span>the circumference of its base is three miles, and the +rim of the crater itself, which is oval in form, is +1331 yards in its larger diameter. The interior is +cultivated by Circassians, and is very fruitful; the +walls descend at an angle of about 30° on the inside, +the exterior slope of the mountain being about 22°. +The cone seems to be formed chiefly of scoriæ, and +the lava-stream, which issues forth from the interior, +forms a frightfully stony and lacerated district.<a name="FNanchor_7_110" id="FNanchor_7_110"></a><a href="#Footnote_7_110" class="fnanchor">[7]</a></p> + +<div class="figcenter"> +<a name="FIGURE_24"> + <img src="images/figure24.jpg" alt="Craters in the Jaulân" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 24.</span>—Extinct Craters in the Jaulân, north-east from the Sea of +Galilee, called Tell Abû en Nedâ and Tell el Urâm, with a central +cone.—(After Schumacher.) +</td></tr> +</table> +</div> + +<p>Another remarkable volcano is the Tell Abû en +Nedâ (<a href="#FIGURE_24">Fig. 24</a>). This is a double crater, with a +cone (probably of cinders) rising from the interior +of one of them. The highest point of the rim of +one of the craters reaches a level of 4042 feet above +the sea. A lava-stream issues forth from Abû en +Nedâ, and unites with another from a neighbouring +volcano.</p> + +<p><span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span></p><p>Tell el Ahmâr is a ruptured crater of imposing +aspect, reaching an elevation of 4060 feet, and sending +forth a lava-current, which falls in regular terraces +from the outlet towards the west and north.</p> + +<p>The ruptured crater of Tell el Akkasheh, which +reaches a height of 3400 feet, has a less forbidding +aspect than the greater number of the extinct +volcanoes of this region, owing to the fact that its +sides are covered by oaks, which attain to magnificent +proportions along the summit. Numerous other +volcanic hills occur in this district, but the most +remarkable is that called Tell el Farras (the Hill of +the Horse). It is an isolated mountain, visible from +afar, and reaches an elevation of 3110 feet, or nearly +800 feet above the surrounding plain. The oval +crater of this volcano opens towards the north, and +has a depth of 108 feet below the edge, with moderately +steep sloping sides (17°-32°), while the slope +of the exterior, at first steep, gradually lessens to +20°-21°. These slopes are covered with reddish or +yellowish slag. The above examples will probably +suffice to afford the reader a general idea of the size +and form of the volcanoes in this little known +region.</p> + +<p>It has been stated above that the great lava-floods +have probably been poured forth intermittently. +The statement receives confirmation from the observations +of Canon Tristram, made in the valley of the +Yarmûk.<a name="FNanchor_8_111" id="FNanchor_8_111"></a><a href="#Footnote_8_111" class="fnanchor">[8]</a> This impetuous torrent rushes down a +gorge, sometimes having limestone on one side and a +wall of basalt on the other. This is due to the fact +that the river channel had been eroded before the +volcanic eruptions had commenced; but on the lava-stream +<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span>reaching the channel, it naturally descended +towards the valley of the Jordan along its bed, displacing +the river, or converting it into clouds of +steam. Subsequently the river again hewed out its +channel, sometimes in the lava, sometimes between +this rock and the chalky limestone. But, in addition +to this, it has been observed that there is a bed of +river gravel interposed between two sheets of basalt +in the Yarmûk ravine; showing that after the first +flow of that molten rock the river reoccupied its +channel, which was afterwards invaded by another +molten lava-stream, into which the waters have again +furrowed the channel which they now occupy. The +basaltic sheets descend under the waters of the Sea of +Galilee on the east side, and were probably connected +with those of Safed, crossing the Jordan valley north +of that lake; owing to this the waters of the Lake of +Merom (Huleh) were pent up, and formerly covered +an extensive tract, now formed of alluvial deposits.</p> + +<p>(<i>d.</i>) <i>Land of Moab.</i>—Proceeding southwards into +the Land of Moab, the volcanic phenomena are here +of great interest. Extensive sheets of basaltic lava, +described as far back as 1807 by Seetzen, and more +recently by Lartet and Tristram, are found at intervals +between the Wâdies Mojib (Arnon) and Haidan. On +either side of the Mojib, cliffs of columnar basalt are +seen capping the beds of white Cretaceous limestone, +while a large mass has descended into the W. +Haidan between cliffs of limestone and marl on either +hand.</p> + +<p>Around Jebel Attarus—a dome-shaped hill of limestone—a +sheet of basaltic lava has been poured, and +has descended the deep gorge of the Zerka Maïn, +which enters the Dead Sea some 2000 feet below. +<span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span>This gorge had been eroded before the basaltic +eruption, so that the stream of molten lava took its +course down the bed of this stream to the water's +edge, and grand sections have been laid bare by +subsequent erosion along the banks. Pentagonal +columns of black basalt form perpendicular walls, +first on one side, then on the other; while considerable +masses of scoriæ, peperino, and breccia appear at the +head of the glen, probably marking the orifice of +eruption. Other eruptions of basalt occur, one at +Mountar ez Zara, to the south of Zerka Maïn, and +another at Wady Ghuweir, near the north-eastern +end of the Dead Sea. There are no lava-streams on +the western side of the Ghor, or of the Dead Sea.<a name="FNanchor_9_112" id="FNanchor_9_112"></a><a href="#Footnote_9_112" class="fnanchor">[9]</a></p> + +<p>The outburst of the celebrated thermal springs of +Callirrhoë, together with nine or ten others, along the +channel of the Zerka Maïn, is a circumstance which +cannot be dissociated from the occurrence of basaltic +lava at this spot. In a reach of three miles, according +to Tristram, there are ten principal springs, of which +the fifth in descent is the largest; but the seventh +and eighth, about half a mile lower down, are the +most remarkable, giving forth large supplies of sulphurous +water. The tenth and last is the hottest of +all, indicating a temperature of 143° Fahr. Thus it +would appear that the heat increases with the depth +from the upper surface of the table-land; a result +which might be expected, supposing the heated +volcanic rocks to be themselves the source of the high +temperature. To a similar cause may be attributed +the hot-springs of Hammath, near Tiberias, and those +of the Yarmûk near its confluence with the Jordan. +<span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span>Some of these and other springs break out along, or +near, the line of the great Jordan-Arabah fault which +ranges throughout the whole extent of this depression, +from the base of Hermon to the Gulf of Akabah, +generally keeping close to the eastern margin of the +valley.</p> + +<p>(<i>e.</i>) <i>The Arabian Desert.</i>—The basaltic lava-floods +occupy a very large extent of the Arabian Desert, +from El Hisma (lat. 27° 35' N.) to the neighbourhood +of Mecca on the south, a distance of about 440 miles, +with occasional intervals. The lava-sheets are called +"Harras" (or "Harrat"), one of which, Harrat Sfeina, +terminates about ten miles north of Mecca. The +lava-sheets rest sometimes on the red sandstone, at +other times, on the granite and other crystalline rocks +of great geological antiquity. In addition to the +sheets of basalt, numerous crater-cones rise from the +basaltic platform at a level of 5000 feet above the sea, +and two volcanic mountains, rising far to the west +of the principal range, called respectively Harrât +Jeheyma and H. Rodwa, almost overlook the coast +of the Red Sea.<a name="FNanchor_10_113" id="FNanchor_10_113"></a><a href="#Footnote_10_113" class="fnanchor">[10]</a></p> + +<p>(<i>f.</i>) <i>Age of the Volcanic Eruptions.</i>—It is very clear +that the first eruptions, producing the great basaltic +sheets of Moab and Arabia, occurred after the principal +features of the country had been developed. The +depression of the Jordan-Arabah valley, the elevation +of the eastern side of this valley along the great +fault line, and the channels of the principal tributary +streams, such as those of the Yarmûk and Zerka +Maïn, all these had been eroded out before they were +invaded by the molten streams of lava. Now, as these +<span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span>physical features were developed and sculptured out +during the Miocene period, as I have elsewhere shown +to be the case,<a name="FNanchor_11_114" id="FNanchor_11_114"></a><a href="#Footnote_11_114" class="fnanchor">[11]</a> we may with great probability refer the +volcanic eruptions to the geological epoch following—namely, +the Pliocene. How far downwards towards +the historic period the eruptions continued is not so +certain. Dr. Daubeny, quoting several passages from +the Old Testament prophets,<a name="FNanchor_12_115" id="FNanchor_12_115"></a><a href="#Footnote_12_115" class="fnanchor">[12]</a> says it might be inferred +that volcanoes were in activity even so late as to +admit of their being included within the limits of +authentic history. The poetic language and imagery +used in these passages by the prophets certainly lends +a probability to this view, but nothing more. On the +other hand, these regions have suffered through many +centuries from the secondary effects of seismic action +and subterranean forces, and earthquake shocks have +laid in ruins the great temples and palaces of Palmyra, +Baalbec, and other cities of antiquity. The +same uncertainty regarding the time at which volcanic +action died out, with reference to the appearance of +man on the scene, hangs over the region of Arabia +and Syria, as we have seen to be the case in reference +to the extinct volcanoes of Auvergne, the Eifel, and +the Lower Rhine. In all these cases the commencement +and close of eruptive action appear to have +been very much about the same period—namely, the +Miocene period on the one hand, and that at which +man entered upon the scene on the other; but in the +case of Syria and Western Palestine, the close of the +volcanic period may have been somewhat more than +2000 <span class="smcap">B.C.</span></p> + +<div class="footnote"><p><a name="Footnote_1_104" id="Footnote_1_104"></a><a href="#FNanchor_1_104"><span class="label">[1]</span></a> Lake Phiala, near the Lake of Huleh, is also situated to the west +of the Jordan valley. Its origin, according to Tristram, is volcanic.</p></div> + +<div class="footnote"><p><a name="Footnote_2_105" id="Footnote_2_105"></a><a href="#FNanchor_2_105"><span class="label">[2]</span></a> Schumacher, "The Jaulân," <i>Quarterly Statement of the Palestine +Exploration Fund</i>, 1886 and 1888; and <i>Across the Jordan</i>, London, +1886.</p></div> + +<div class="footnote"><p><a name="Footnote_3_106" id="Footnote_3_106"></a><a href="#FNanchor_3_106"><span class="label">[3]</span></a> Lartet, <i>Voyage d'Exploration de la mer Morte</i> (Géologie), Paris, +1880.</p></div> + +<div class="footnote"><p><a name="Footnote_4_107" id="Footnote_4_107"></a><a href="#FNanchor_4_107"><span class="label">[4]</span></a> Tristram, <i>Land of Moab</i>, London, 1873; and <i>Land of Israel</i>, 1866.</p></div> + +<div class="footnote"><p><a name="Footnote_5_108" id="Footnote_5_108"></a><a href="#FNanchor_5_108"><span class="label">[5]</span></a> Niebuhr, <i>Beschreibung von Arabien</i>, 1773.</p></div> + +<div class="footnote"><p><a name="Footnote_6_109" id="Footnote_6_109"></a><a href="#FNanchor_6_109"><span class="label">[6]</span></a> C. M. Doughty, <i>Arabia Deserta</i>, 2 vols., 1888. A generalised +account of this volcanic region by the author will be found in the +"Memoir on the Physical Geology of Arabia Petræa, and Palestine," +<i>Palestine Exploration Fund</i>, 1887.</p></div> + +<div class="footnote"><p><a name="Footnote_7_110" id="Footnote_7_110"></a><a href="#FNanchor_7_110"><span class="label">[7]</span></a> Schumacher, <i>loc. cit.</i>, p. 248.</p></div> + +<div class="footnote"><p><a name="Footnote_8_111" id="Footnote_8_111"></a><a href="#FNanchor_8_111"><span class="label">[8]</span></a> <i>Land of Israel</i>, p. 461.</p></div> + +<div class="footnote"><p><a name="Footnote_9_112" id="Footnote_9_112"></a><a href="#FNanchor_9_112"><span class="label">[9]</span></a> "Geology of Arabia Petræa, and Palestine," <i>Memoirs of the +Palestine Exploration Fund</i>, p. 95.</p></div> + +<div class="footnote"><p><a name="Footnote_10_113" id="Footnote_10_113"></a><a href="#FNanchor_10_113"><span class="label">[10]</span></a> Doughty, <i>loc. cit.</i>, vol. i., plate vi., p. 416. An excellent geological +sketch map accompanies this work.</p></div> + +<div class="footnote"><p><a name="Footnote_11_114" id="Footnote_11_114"></a><a href="#FNanchor_11_114"><span class="label">[11]</span></a> "Memoir of the Geology of Arabia Petræa, and Palestine," chap. +vi. p. 67.</p></div> + +<div class="footnote"><p><a name="Footnote_12_115" id="Footnote_12_115"></a><a href="#FNanchor_12_115"><span class="label">[12]</span></a> Nahum, i. 5, 6; Micah, i. 3, 4; Isaiah, lxiv. 1-3; Jeremiah, l. 25.</p></div> +<p><span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_III_CHAPTER_II" id="PART_III_CHAPTER_II"></a>CHAPTER II. +<br /><br /> +THE VOLCANIC REGIONS OF NORTH AMERICA.</h2> + + +<p>(<i>a.</i>) <i>Contrast between the Eastern and Western +Regions.</i>—In no point is there a more remarkable +contrast between the physical structure of Eastern +and Western America than in the absence of volcanic +phenomena in the former and their prodigious development +in the latter. The great valley of the Mississippi +and its tributaries forms the dividing territory +between the volcanic and non-volcanic areas; so that +on crossing the high ridges in which the western +tributaries of America's greatest river have their +sources, and to which the name of the "Rocky Mountains" +more properly belongs, we find ourselves in a +region which, throughout the later Tertiary times down +almost to the present day, has been the scene of +volcanic operations on the grandest scale; where +lava-floods have been poured over the country through +thousands of square miles, and where volcanic cones, +vying in magnitude with those of Etna, Vesuvius, or +Hecla, have established themselves. This region, +generally known as "The Great Basin," is bounded +on the west by the "Pacific Range" of mountains, +and includes portions of New Mexico, Arizona, +California, Nevada, Utah, Colorado, Idaho, Oregon, +Wyoming, Montana, and Washington. To the south +<span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span>it passes into the mountainous region of Mexico, also +highly volcanic; and thence into the ridge of Panama +and the Andes. It cannot be questioned but that +the volcanic nature of the Great Basin is due to the +same causes which have originated the volcanic outbursts +of the Andes; but, from whatever cause, the +volcanic forces have here entered upon their secondary +or moribund stage. In the Yellowstone Valley, +geysers, hot springs, and fumaroles give evidence of +this condition. In other districts the lava-streams +are so fresh and unweathered as to suggest that they +had been erupted only a few hundred years ago; but +no active vent or crater is to be found over the whole +of this wide region. A few special districts only can +here be selected by way of illustration of its special +features in connection with its volcanic history.</p> + +<p>(<i>b.</i>) <i>The Plateau Country of Utah and Arizona.</i>—This +tract, which is drained by the Colorado River +and its tributaries, is bounded on the north by the +Wahsatch range, and extends eastwards to the base +of the Sierra Nevada. Round its margin extensive +volcanic tracts are to be found, with numerous peaks +and truncated cones—the ancient craters of eruption—of +which Mount San Francisco is the culminating +eminence. South of the Wahsatch, and occupying the +high plateaux of Utah, enormous masses of volcanic +products have been spread over an area of 9000 square +miles, attaining a thickness of between 3000 and 4000 +feet. The earlier of these great lava-floods appear to +have been trachytic, but the later basaltic; and in the +opinion of Captain Dutton, who has described them, +they range in point of time from the Middle Tertiary +(Miocene) down to comparatively recent times.</p> + +<p>(<i>c.</i>) <i>The Grand Cañon.</i>—To the south of the high +<span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span>plateaux of Utah are many minor volcanic mountains, +now extinct; and as we descend towards the Grand +Cañon of Colorado we find numerous cinder-cones +scattered about at intervals near the cliffs.<a name="FNanchor_1_116" id="FNanchor_1_116"></a><a href="#Footnote_1_116" class="fnanchor">[1]</a> Extensive +lava-fields, surmounted by cinder-cones, occupy the +plateau on the western side of the Grand Cañon; and, +according to Dutton, the great sheets of basaltic lava, +of very recent age, which occupy many hundred square +miles of desert, have had their sources in these cones of +eruption.<a name="FNanchor_2_117" id="FNanchor_2_117"></a><a href="#Footnote_2_117" class="fnanchor">[2]</a> Crossing to the east of the Grand Cañon, +we find other lava-floods poured over the country at +intervals, surmounted by San Francisco—a volcanic +mountain of the first magnitude—which reaches an +elevation, according to Wheeler, of 12,562 feet above +the ocean. It has long been extinct, and its summit +and flanks are covered with snow-fields and glaciers. +Other parts of Arizona are overspread by sheets of +basaltic lava, through which old "necks" of eruption, +formed of more solid lava than the sheets, rise occasionally +above the surface, and are prominent features in +the landscape.</p> + +<p>Further to the eastward in New Mexico, and near +the margin of the volcanic region, is another volcanic +mountain little less lofty than San Francisco, called +Mount Taylor, which, according to Dutton, rises to +an elevation of 11,390 feet above the ocean, and 8200 +feet above the general level of the surrounding plateau +of lava. This mountain forms the culminating point +of a wide volcanic tract, over which are distributed +<span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span>numberless vents of eruption. Scores of such vents—generally +cinder-cones—are visible in every part +of the plateau, and always in a more or less dilapidated +condition.<a name="FNanchor_3_118" id="FNanchor_3_118"></a><a href="#Footnote_3_118" class="fnanchor">[3]</a> Mount Taylor is a volcano, with a +central pipe terminating in a large crater, the wall of +which was broken down on the east side in the later +stage of its history.</p> + +<div class="figcenter"> +<a name="FIGURE_25"> + <img src="images/figure25.jpg" alt="Mount Shasta" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 25.</span>—Mount Shasta (14,511 feet), a snow-clad volcanic cone in California, with Mount Shastina, a secondary crater, +on the right; the valley between is filled with glacier-ice.—(After Dutton). +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span></p><p>(<i>d.</i>) <i>California.</i>—Proceeding westwards into California, +we are again confronted with volcanic phenomena +on a stupendous scale. The coast range of +mountains, which branches off from the Sierra +Nevada at Mount Pinos, on the south, is terminated +near the northern extremity of the State by a very +lofty mountain of volcanic origin, called Mount +Shasta, which attains an elevation of 14,511 feet +(see <a href="#FIGURE_25">Fig. 25</a>). This mountain was first ascended by +Clarence King in 1870,<a name="FNanchor_4_119" id="FNanchor_4_119"></a><a href="#Footnote_4_119" class="fnanchor">[4]</a> and although forming, as +it were, a portion of the Pacific Coast Range, it +really rises from the plain in solitary grandeur, its +summit covered by snow, and originating several +fine glaciers.</p> + +<p>The summit of Mount Shasta is a nearly perfect +cone, but from its north-west side there juts out a +large crater-cone just below the snow-line, between +which and the main mass of the mountain there +exists a deep depression filled with glacier ice. This +secondary crater-cone has been named Mount +Shastina, and round its inner side the stream of +glacier ice winds itself, sometimes surmounting the +rim of the crater, and shooting down masses of ice +<span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span>into the great caldron. The length of this glacier is +about three miles, and its breadth about 4000 feet. +Another very lofty volcanic mountain is Mount +Rainier, in the Washington territory, consisting of +three peaks of which the eastern possesses a crater +very perfect throughout its entire circumference. +This mountain appears to be formed mainly of +trachytic matter. Proceeding further north into +British territory, several volcanic mountains near +the Pacific Coast are said to exhibit evidence of +activity. Of these may be mentioned Mount Edgecombe, +in lat. 57°.3; Mount Fairweather, lat. 57°.20 +which rises to a height of 14,932 feet; and Mount +St. Elias, lat. 60°.5, just within the divisional line +between British and Russian territory, and reaching +an altitude of 16,860 feet. This, the loftiest of all the +volcanoes of the North American continent, except +those of Mexico, may be considered as the connecting +link in the volcanic chain between the continent +and the Aleutian Islands.<a name="FNanchor_5_120" id="FNanchor_5_120"></a><a href="#Footnote_5_120" class="fnanchor">[5]</a></p> + +<p>(<i>e.</i>) <i>Lake Bonneville.</i>—Returning to Utah we are +brought into contact with phenomena of special +interest, owing to the inter-relations of volcanic and +lacustrine conditions which once prevailed over large +tracts of that territory. The present Great Salt +Lake, and the smaller neighbouring lakes, those called +Utah and Sevier, are but remnants of an originally +far greater expanse of inland water, the boundaries +of which have been traced out by Mr. C. K. Gilbert, +and described under the name of Lake Bonneville.<a name="FNanchor_6_121" id="FNanchor_6_121"></a><a href="#Footnote_6_121" class="fnanchor">[6]</a> +The waters of this lake appear to have reached their +highest level at the period of maximum cold of the +<span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span>Post-Pliocene period, when the glaciers descended +to its margin, and large streams of glacier water +were poured into it. Eruptions of basaltic lava from +successive craters appear to have gone on before, +during, and after the lacustrine epochs; and the drying +up of the waters over the greater extent of their +original area, now converted into the Sevier Desert, +and their concentration into their present comparatively +narrow basins, appears to have proceeded <i>pari +passu</i> with the gradual extinction of the volcanic outbursts. +Two successive epochs of eruption of basalt +appear to have been clearly established—an earlier +one of the "Provo Age," when the lava was extruded +from the Tabernacle craters, and a later epoch, when +the eruptions took place from the Ice Spring craters. +The oldest volcanic rock appears to be rhyolite, +which peers up in two small hills almost smothered +beneath the lake deposits. Its eruption was long +anterior to the lake period. On the other hand, the +cessation of the eruptions of the later basaltic sheets +is evidently an event of such recent date that Mr. +Gilbert is led to look forward to their resumption at +some future, but not distant, epoch. As he truly +observes, we are not to infer that, because the outward +manifestations of volcanic action have ceased, +the internal causes of those manifestations have +passed away. These are still in operation, and must +make themselves felt when the internal forces have +recovered their exhausted energies; but perhaps not +to the same extent as before.</p> + +<p>(<i>f.</i>) <i>Region of the Snake River.</i>—The tract of +country bordering the Snake River in Idaho and +Washington is remarkable for the vast sheets of +plateau-basalt with which it is overspread, extending +<span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span>sometimes in one great flood farther than the eye can +reach, and what is still more remarkable, they are +often unaccompanied by any visible craters or vents +of eruption. In Oregon the plateau-basalt is at least +2,000 feet in thickness, and where traversed by the +Columbia River it reaches a thickness of about 3,000 +feet. The Snake and Columbia rivers are lined by +walls of volcanic rock, basaltic above, trachytic below, +for a distance of, in the former, one hundred, in the +latter, two hundred, miles. Captain Dutton, in describing +the High Plateau of Utah, observes that the +lavas appear to have welled up in mighty floods +without any of that explosive violence generally +characteristic of volcanic action. This extravasated +matter has spread over wide fields, deluging the +surrounding country like a tide in a bay, and overflowing +all inequalities. Here also we have evidence +of older volcanic cones buried beneath seas of lava +subsequently extruded.</p> + +<p>(<i>g.</i>) <i>Fissures of Eruption.</i>—The absence, or rarity, of +volcanic craters or cones of eruption in the neighbourhood +of these great sheets has led American geologists +to the conclusion that the lavas were in many cases +extruded from fissures in the earth's crust rather than +from ordinary craters.<a name="FNanchor_7_122" id="FNanchor_7_122"></a><a href="#Footnote_7_122" class="fnanchor">[7]</a> This view is also urged by +Sir A. Geikie, who visited the Utah region of the +Snake River in 1880, and has vividly described the +impression produced by the sight of these vast fields +of basaltic lava. He says, "We found that the older +trachytic lavas of the hills had been deeply trenched +by the lateral valleys, and that all these valleys had a +floor of black basalt that had been poured out as the last +<span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span>of the molten materials from the now extinct volcanoes. +There were no visible cones or vents from which these +floods of basalt could have proceeded. We rode for +hours by the margin of a vast plain of basalt stretching +southward and westward as far as the eye could +reach.... I realised the truth of an assertion made +first by Richthofen,<a name="FNanchor_8_123" id="FNanchor_8_123"></a><a href="#Footnote_8_123" class="fnanchor">[8]</a> that our modern volcanoes, such +as Vesuvius and Etna, present us with by no means +the grandest type of volcanic action, but rather belong +to a time of failing activity. There have been periods +of tremendous volcanic energy, when instead of +escaping from a local vent, like a Vesuvian cone, the +lava has found its way to the surface by innumerable +fissures opened for it in the solid crust of the globe +over thousands of square miles."<a name="FNanchor_9_124" id="FNanchor_9_124"></a><a href="#Footnote_9_124" class="fnanchor">[9]</a></p> + +<p>(<i>h.</i>) <i>Volcanic History of Western America.</i>—The +general succession of volcanic events throughout the +region of Western America appears to have been +somewhat as follows:—<a name="FNanchor_10_125" id="FNanchor_10_125"></a><a href="#Footnote_10_125" class="fnanchor">[10]</a></p> + +<p>The earliest volcanic eruptions occurred in the later +Eocene epoch and were continued into the succeeding +Miocene stage. These consisted of rocks moderately +rich in silica, and are grouped under the heads of +propylite and andesite. To these succeeded during +the Pliocene epoch still more highly silicated rocks of +trachytic type, consisting of sanidine and oligoclase +trachytes. Then came eruptions of rhyolite during +the later Pliocene and Pleistocene epochs; and lastly, +after a period of cessation, during which the rocks +just described were greatly eroded, came the great +<span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span>eruptions of basaltic lava, deluging the plains, winding +round the cones or plateaux of the older lavas, +descending into the river valleys and flooding the lake +beds, issuing forth from both vents and fissures, and +continuing intermittently down almost into the present +day—certainly into the period of man's appearance +on the scene. Thus the volcanic history of Western +America corresponds remarkably to that of the European +regions with which we have previously dealt, +both as regards the succession of the various lavas +and the epochs of their eruption.</p> + +<p>(<i>i.</i>) <i>The Yellowstone Park.</i>—The geysers and hot +springs of the Yellowstone Park, like those in Iceland +and New Zealand, are special manifestations of volcanic +action, generally in its secondary or moribund stage. +The geysers of the Yellowstone occur on a grand +scale; the eruptions are frequent, and the water is +projected into the air to a height of over 200 feet. +Most of these are intermittent, like the remarkable +one known as Old Faithful, the Castle Geyser, and +the Giantess Geyser described by Dr. Hayden, which +ejects the water to a height of 250 feet. The +geyser-waters hold large quantities of silica and +sulphur in solution, owing to their high temperature +under great pressure, and these minerals are precipitated +upon the cooling of the waters in the air, and +form circular basins, often gorgeously tinted with red +and yellow colours.<a name="FNanchor_11_126" id="FNanchor_11_126"></a><a href="#Footnote_11_126" class="fnanchor">[11]</a></p> + +<div class="footnote"><p><a name="Footnote_1_116" id="Footnote_1_116"></a><a href="#FNanchor_1_116"><span class="label">[1]</span></a> J. W. Powell, <i>Exploration of the Cañons of the Colorado</i>, pp. 114, +196. Major Powell describes a fault or fissure through which floods of +lava have been forced up from beneath and have been poured over the +surface. Many cinder-cones are planted along the line of this fissure.</p></div> + +<div class="footnote"><p><a name="Footnote_2_117" id="Footnote_2_117"></a><a href="#FNanchor_2_117"><span class="label">[2]</span></a> Capt. C. E. Dutton. <i>Sixth Ann. Rep. U.S. Geol. Survey</i>, +1884-85.</p></div> + +<div class="footnote"><p><a name="Footnote_3_118" id="Footnote_3_118"></a><a href="#FNanchor_3_118"><span class="label">[3]</span></a> Dutton, <i>loc. cit.</i>, chap. iv. p. 165.</p></div> + +<div class="footnote"><p><a name="Footnote_4_119" id="Footnote_4_119"></a><a href="#FNanchor_4_119"><span class="label">[4]</span></a> <i>Amer. Jour. Science</i>, vol. 3., ser. (1871). A beautiful map of this +mountain is given in the <i>Fifth Annual Report, U.S. Geol. Survey</i>, +1883-84. Plate 44.</p></div> + +<div class="footnote"><p><a name="Footnote_5_120" id="Footnote_5_120"></a><a href="#FNanchor_5_120"><span class="label">[5]</span></a> Daubeny, <i>loc. cit.</i>, p. 474.</p></div> + +<div class="footnote"><p><a name="Footnote_6_121" id="Footnote_6_121"></a><a href="#FNanchor_6_121"><span class="label">[6]</span></a> Gilbert, <i>Monograph U.S. Geol. Survey</i>, vol. i. (1890).</p></div> + +<div class="footnote"><p><a name="Footnote_7_122" id="Footnote_7_122"></a><a href="#FNanchor_7_122"><span class="label">[7]</span></a> Powell, <i>Exploration of the Colorado River</i>, p. 177, etc. (1875). +Hayden, <i>Rep. U.S. Geol. Survey of the Colorado, etc.</i> (1871-80).</p></div> + +<div class="footnote"><p><a name="Footnote_8_123" id="Footnote_8_123"></a><a href="#FNanchor_8_123"><span class="label">[8]</span></a> Richthofen, <i>Natural System of Volcanic Rocks</i>, Mem. California +Acad. Sciences, vol. i. (1868).</p></div> + +<div class="footnote"><p><a name="Footnote_9_124" id="Footnote_9_124"></a><a href="#FNanchor_9_124"><span class="label">[9]</span></a> Geikie, <i>Geological Sketches at Home and Abroad</i>, p. 271 (1882).</p></div> + +<div class="footnote"><p><a name="Footnote_10_125" id="Footnote_10_125"></a><a href="#FNanchor_10_125"><span class="label">[10]</span></a> Prestwich, <i>Geology</i>, vol. i. p. 370, quoting from Richthofen.</p></div> + +<div class="footnote"><p><a name="Footnote_11_126" id="Footnote_11_126"></a><a href="#FNanchor_11_126"><span class="label">[11]</span></a> The origin of geysers is variously explained; see Prestwich, <i>Geology</i>, +vol. i. p. 170. They are probably due to heated waters suddenly converted +into steam by contact with rock at a high temperature.</p></div> +<p><span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_III_CHAPTER_III" id="PART_III_CHAPTER_III"></a>CHAPTER III. +<br /><br /> +VOLCANOES OF NEW ZEALAND.</h2> + + +<p>One other region of volcanic action remains to be +noticed before passing on to the consideration of +those of less recent age. New Zealand is an island +wherein seem to be concentrated all the phenomena +of volcanic action of past and present time. Though +it is doubtful if the term "active," in its full sense, +can be applied to any of the existing craters (with two +or three exceptions, such as Tongariro and Whakari +Island), we find craters and cones in great numbers +in perfectly fresh condition, extensive sheets of +trachytic and basaltic lavas, ashes, and agglomerates; +lava-floods descending from the ruptured +craters of ashes and scoriæ; old crater-basins converted +into lakes; geysers, hot springs and fumaroles +which may be counted by hundreds, and cataracts +breaking over barriers of siliceous sinter; and, lastly, +lofty volcanic mountains vying in magnitude with +Vesuvius and Etna. All these wonderful exhibitions +of moribund volcanic action seem to be concentrated +in the northern island of Auckland. The +southern island, which is the larger, also has its +natural attractions, but they are of a different kind; +chief of all is the grand range of mountains called, not +inappropriately, the "Southern Alps," vying with its +European representative in the loftiness of its peaks +<span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span>and the splendour of its snowfields and glaciers, but +formed of more ancient and solid rocks than those +of the northern island.</p> + +<p>(<i>a.</i>) <i>Auckland District.</i>—We are indebted to several +naturalists for our knowledge of the volcanic regions +of New Zealand, but chiefly to Ferdinand von Hochstetter, +whose beautiful maps and graphic descriptions +leave nothing to be desired.<a name="FNanchor_1_127" id="FNanchor_1_127"></a><a href="#Footnote_1_127" class="fnanchor">[1]</a> In this work Hochstetter +was assisted by Julius Haast and Sir J. Hector. +From their account we learn that the Isthmus of +Auckland is one of the most remarkable volcanic +districts in the world. It is characterised by a large +number of extinct cinder-cones, in a greater or less +perfect state of preservation, and giving origin to +lava-streams which have poured down the sides of +the hills on to the plains. Besides these are others +formed of stratified tuff, with interior craters, surrounding +in mural cliffs eruptive cones of scoriæ, +ashes, and lapilli; these cones are scattered over the +isthmus and shores of Waitemata and Manukau. +The tuff cones and craters rise from a floor of Tertiary +sandstone and shale, the horizontal strata of which +are laid open in the precipitous bluffs of Waitemata +and Manukau harbours; they sometimes contain +fossil shells of the genera <i>Pecten</i>, <i>Nucula</i>, <i>Cardium</i>, +<i>Turbo</i>, and <i>Neritæ</i>. As the volcanic tuff-beds are +intermingled with the Upper Tertiary strata, it is +inferred that the first outbursts of volcanic forces +occurred when the region was still beneath the waters +of the ocean. Cross-sections show that the different +layers slope both outwards (parallel to the sides) and +<span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span>inwards towards the bottom of the craters. Sometimes +these craters have been converted into lakes, as +in the case of those of the Eifel; but generally they are +dry or have a floor of morass. Of the crater-lakes, +those of Kohuora, five in number, are perhaps the +most remarkable; and in the case of two of these +the central cones of slag appear as islets rising from +the surface of the waters. The fresh-water lake +Pupuka has a depth of twenty-eight fathoms. To +the north of Auckland Harbour rises out of the waters +of the Hauraki Gulf the cone of Rangitoto, 920 feet +high, the flanks formed of rugged streams of basalt, +and the summit crowned by a circular crater of slag +and ash, out of the centre of which rises a second +cone with the vent of eruption. This is the largest +and newest of the Auckland volcanoes, and appears +to have been built up by successive outpourings of +basaltic lava from the central orifice, after the general +elevation of the island.</p> + +<div class="figcenter"> +<a name="FIGURE_26"> + <img src="images/figure26.jpg" alt="Forms of volcanic tuff cones" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 26.</span>—Forms of volcanic tuff cones, with their cross-sections, in +the Province of Auckland.—No. 1. Simple tuff cone with central crater; +No. 2. Outer tuff cone with interior cinder cone and crater; No. 3. +The same with lava-stream issuing from the interior cone.—(After Hochstetter.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span></p><p>Before leaving the description of the tuff-cones, +which are a peculiar feature in the volcanic phenomena +of New Zealand, and are of many forms +and varieties, we must refer to that of Mount +Wellington (Maunga Rei). This is a compound +volcano, in which the oldest and smallest of the +group is a tuff-crater-cone, exhibiting very beautifully +the outward slope of its beds. Within this +crater arise two cones of cinders, each with small +craters. It would appear that after a long interval +the larger of the two principal cones, formed of +cinders and known as Mount Wellington, burst +forth from the southern margin of the older tuff-cone, +and, being built up to a height of 850 feet, +gradually overspread the sides of its older neighbour. +Mount Wellington itself has three craters, and from +these large streams of basaltic lava have issued forth +in a westerly direction, while a branch entered and +partially filled the old tuff-crater to the northwards.</p> + +<p><span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span></p><p>Southwards from Manukau Harbour, and extending +a short distance from the coast-line to +Taranaki Point, there occurs a plateau of basalt-conglomerate +(<i>Basaltkonglomerat</i>), with sheets of +basaltic lava overspreading the Tertiary strata. +These plateau-basalts are intersected by eruptive +masses in the form of dykes, but still there are no +craters or cones of eruption to be seen; so that we +may infer that the sheets, at least, were extruded +from fissures in the manner of those of the Colorado +or Idaho regions of America. Proceeding still +further south into the interior of the island, we +here find a lofty plateau of an average elevation +of 2,000 feet, interposed between the Tertiary beds +of the Upper and Middle Waikato, and formed of +trachytic and pitch-stone tuff, amongst which arise +old extinct volcanic cones, such as those of Karioi, +Pirongia, Kakepuku, Maunga Tautari, Aroha, and +many others. These trachytic lavas would seem +to be more ancient than the basaltic, previously +described.</p> + +<p>(<i>b.</i>) <i>Taupo Lake, and surrounding district.</i>—But of +all these volcanic districts, none is more remarkable +than that surrounding the Taupo Lake, which lies +amidst the Tertiary strata of the Upper Waikato +Basin. The surface of this lake is 1,250 feet above +that of the ocean, and its margin is enclosed within +a border of rhyolite and pitchstone—rising into +a mass of the same material 1,800 feet high on the +eastern side. The form of the lake does not suggest +that it is itself the crater of a volcano, but rather that +it was originated by subsidence. On all sides, however, +trachytic cones arise, of which the most remarkable +group lies to the south of the lake, just +<span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span>in front of the two giant trachytic cones, the loftiest +in New Zealand, one called Tongariro, rising about +6,500 feet, and the other Ruapahu, which attains an +elevation of over 9,000 feet, with the summit capped +by snow. These two lofty cones, standing side by +side, are supposed by the Maoris to be the husband +and wife to whom were born the group of smaller +cones above referred to as occupying the southern +shore of Taupo Lake. The volcano of Tongariro +may still be considered as in a state of activity, as +its two craters (Ngauruhoe and Ketetahi) constantly +emit steam, and several solfataras break out on its +flanks.<a name="FNanchor_2_128" id="FNanchor_2_128"></a><a href="#Footnote_2_128" class="fnanchor">[2]</a></p> + +<p>(<i>c.</i>) <i>Roto Mahana.</i>—In a northerly direction from +Tongariro, and distant from the coast by a few +miles, lies in the Bay of Plenty the second of the +active volcanoes of New Zealand, the volcanic island +of Whakari (White Island), from the crater of which +are constantly erupted vast masses of steam clouds. +The distance between these two active craters +is 120 nautical miles; and along the tract joining +them steam-jets and geysers issue forth from the +deep fissures through which the lava sheets have +formerly been extruded. Numerous lakes also +occupy the larger cavities in the ground; and hot-springs, +steam-fumaroles and solfataras burst out +in great numbers along the banks of the Roto +Mahana Lake and the Kaiwaka River by which +it is drained. Amongst such eruptions of hot-water +and steam we might expect the formation of siliceous +sinter, and the deposition of sulphur and other +minerals; nor will our expectations be disappointed. +<span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span>For here we have the wonderful terraces of siliceous +sinter deposited by the waters entering Roto Mahana +as they descend from the numerous hot-springs or +pools near its margin. All travellers concur in +describing these terraces as the most wonderful +of all the wonders of the Lake district of New +Zealand—so great is their extent, and so rich and +varied is their colouring.</p> + +<p>The beautiful map of Roto Mahana on an enlarged +scale by Hochstetter shows no fewer than ten large +sinter terraces descending towards the margin of this +lake, besides several mud-springs, fumaroles, and +solfataras. But the largest and most celebrated of +all the sinter terraces has within the last few years +been buried from view beneath a flood of volcanic +trass, or mud, an event which was as unexpected +as it was unwelcome. In May, 1887, the mountain +of Tarawera, which rises to the north-east of Roto +Mahana, and on the line of eruption above described, +suddenly burst forth into violent activity, covering +the country for miles around with clouds of ashes, +and, pouring down torrents of mud, completely +enveloped the beautiful terrace of sinter which had +previously been one of the wonders of New Zealand. +By the same eruption several human beings were +entombed, and their residences destroyed.</p> + +<p>The waters of Roto Mahana, together with the +hot-springs and fountains are fed from rain, and +from the waters of Taupo Lake, which, sinking +through fissures in the ground, come in contact with +the interior heated matter, and thus steam at high +temperature and pressure is generated.<a name="FNanchor_3_129" id="FNanchor_3_129"></a><a href="#Footnote_3_129" class="fnanchor">[3]</a></p> + +<p><span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span></p><p>(<i>d.</i>) <i>Moribund condition of New Zealand Volcanoes.</i>—From +what has been said, it will be inferred that in +the case of New Zealand, as in those of Auvergne, +the Eifel and Lower Rhine, Arabia, and Western +America, we have an example of a region wherein +the volcanic forces are well-nigh spent, but in which +they were in a state of extraordinary activity +throughout the later Tertiary, down to the commencement +of the present epoch. In most of these +cases the secondary phenomena of vulcanicity are +abundantly manifest; but the great exhibitions of +igneous action, when the plains were devastated by +sheets of lava, and cones and craters were piled up +through hundreds and thousands of feet, have for the +present, at least, passed away.</p> + +<div class="footnote"><p><a name="Footnote_1_127" id="Footnote_1_127"></a><a href="#FNanchor_1_127"><span class="label">[1]</span></a> <i>Geol.-topographischer Atlas von Neu-Seeland</i>, von Dr. Ferd. von +Hochstetter und Dr. A. Petermann. Gotha: Justus Perthes (1863). +Also <i>New Zealand</i>, trans. by E. Sauter, Stuttgart (1867).</p></div> + +<div class="footnote"><p><a name="Footnote_2_128" id="Footnote_2_128"></a><a href="#FNanchor_2_128"><span class="label">[2]</span></a> Tongariro was visited in 1851 by Mr. H. Dyson, who describes the +eruption of steam.</p></div> + +<div class="footnote"><p><a name="Footnote_3_129" id="Footnote_3_129"></a><a href="#FNanchor_3_129"><span class="label">[3]</span></a> Mr. Froude figures and describes the two terraces, the "White" +and "Pink," in <i>Oceana</i>, 2nd edition, pp. 285-291.</p></div> +<p><span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span></p> + + +<hr class="major" /> +<h1><a name="PART_IV" id="PART_IV"></a>PART IV. +<br /><br /> +TERTIARY VOLCANIC DISTRICTS OF THE +BRITISH ISLES.</h1> + + + +<hr class="major" /> +<h2><a name="PART_IV_CHAPTER_I" id="PART_IV_CHAPTER_I"></a>CHAPTER I. +<br /><br /> +ANTRIM.</h2> + + +<p>It is an easy transition to pass from the consideration +of European and other dormant, or extinct, +volcanic regions to those of the British Isles, +though the volcanic forces may have become in +this latter instance quiescent for a somewhat longer +period. In all the cases we have been considering, +whether those of Central Italy, of the Rhine and +Moselle, of Auvergne, or of Syria and Arabia, the +cones and craters of eruption are generally present +entire, or but slightly modified in form and size by +the effects of time. But in the case of the Tertiary +volcanic districts of the British Isles this is not so. +On the contrary, these more prominent features of +vulcanicity over the surface of the ground have been +removed by the agents of denudation, and our +observations are confined to the phenomena presented +by extensive sheets of lava and beds of ash, +or the stumps and necks of former vents of eruption, +<span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span>together with dykes of trap by which the plateau-lavas +are everywhere traversed or intersected.</p> + +<p>The volcanic region of the British Isles extends at +intervals from the North-east of Ireland through the +Island of Mull and adjoining districts on the mainland +of Morvern and Ardnamurchan into the Isle of Skye, +and comprises several smaller islets; the whole being +included in the general name of the Inner Hebrides. +It is doubtful if the volcanic lavas of Co. Antrim were +ever physically connected with those of the west of +Scotland, though they may be considered as contemporary +with them; and in all cases the existing +tracts of volcanic rock are mere fragments of those +originally formed by the extrusion of lavas from +vents of eruption. In addition to these, there are +large areas of volcanic rock overspread by the waters +of the ocean.</p> + +<p>(<i>a.</i>) <i>Geological Age.</i>—The British volcanic eruptions +now under consideration are all later than the Cretaceous +period. Throughout Antrim, and in parts of +Mull, the lavas are found resting on highly eroded +faces either of the Upper Chalk (<a href="#FIGURE_27">Fig. 27</a>), or, where it +has been altogether denuded away, on still older Mesozoic +strata. From the relations of the basaltic sheets of +Antrim to the Upper Chalk, it is clear that the latter +formation, after its deposition beneath the waters of +the Cretaceous seas, was elevated into dry land and +exposed to a long period of subaërial erosion before +the first sheets of lava invaded the surface of the +ground. We are, therefore, tolerably safe in considering +the first eruptions to belong to the Tertiary +period; but the evidence, derived as it is exclusively +from plant remains, is somewhat conflicting as to the +precise epoch to which the lavas and beds of tuff +<span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span>containing the plant-remains are to be referred. The +probabilities appear to be that they are of Miocene +age; and if so, the trachytic lavas, which in Antrim +are older than those containing plants, may be referred +to a still earlier epoch—namely, that of the Eocene.<a name="FNanchor_1_130" id="FNanchor_1_130"></a><a href="#Footnote_1_130" class="fnanchor">[1]</a> +As plant remains are not very distinctive, the question +regarding the exact time of the first volcanic eruptions +will probably remain for ever undecided; but +we are not likely to be much in error if we consider +the entire volcanic period to range from the close of +the Eocene to that of the Miocene; by far the greater +mass of the volcanic rocks being referable to the +latter epoch.</p> + +<p>In describing the British volcanic districts it will be +most convenient to deal with them in three divisions—viz., +those of Antrim, Mull, and Skye, commencing +with Antrim.<a name="FNanchor_2_131" id="FNanchor_2_131"></a><a href="#Footnote_2_131" class="fnanchor">[2]</a></p> + +<p>(<i>b.</i>) <i>Volcanic Area.</i>—The great sheets of basalt and +other volcanic products of the North-east of Ireland +overspread almost the whole of the County Antrim, +and adjoining districts of Londonderry and Tyrone, +breaking off in a fine mural escarpment along the +<span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span>northern shore of Belfast Lough and the sea coast +throughout the whole of its range from Larne +Harbour to Lough Foyle; the only direction in which +these features subside into the general level of the +country being around the shores of Lough Neagh. +Several outliers of the volcanic sheets are to be found +at intervals around the great central plateau; such as +those of Rathlin Island, Island Magee, and Scrabo +Hill in Co. Down. The area of the basaltic plateau +may be roughly estimated at 2,000 square miles.</p> + +<div class="figcenter"> +<a name="FIGURE_27"></a> +<a href="images/figure27full.jpg"> + <img src="images/figure27.jpg" alt="The White Rocks" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 27.</span>—"The White Rocks," Portrush, Co. Antrim, showing the plateau-basalt resting on an eroded surface of the Upper +Chalk, with bands of flint.—(From a photograph.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_158" id="Page_158">[Pg 158]</a></span></p><p>The truncated edges of this marginal escarpment +rising to levels of 1,000 to 1,260 feet, as in the case of +Benevenagh in Co. Derry, and 1,825 feet at Mullaghmore, +attest an originally greatly more extended +range of the basaltic sheets; and it is not improbable +that at the close of the Miocene epoch they extended +right across the present estuary of Lough Foyle to +the flanks of the mountains of Inishowen in Donegal +in one direction, and to those of Slieve Croob in the +other. In the direction of Scotland the promontories +of Kintyre and Islay doubtless formed a part of the +original margin. Throughout this vast area the volcanic +lavas rest on an exceedingly varied rocky floor, +both as regards composition and geological age. (See +<a href="#FIGURE_28">Fig. 28</a>.) Throughout the central, southern, eastern, +and northern parts of their extent, the Chalk formation +may be considered to form this floor; but in the +direction of Armagh and Tyrone, towards the southwestern +margin, the basaltic sheets are found resting +indiscriminately on Silurian, Carboniferous, and +Triassic strata. The general relations of the plateau-basalts +to the underlying formations show, that at the +close of the Cretaceous period there had been considerable +terrestrial disturbances and great subaërial +<span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span>denudation, resulting in some cases in the complete +destruction of the whole of the Cretaceous strata, +before the lava floods were poured out; owing to +which, these latter are found resting on formations of +older date than the Cretaceous.<a name="FNanchor_3_132" id="FNanchor_3_132"></a><a href="#Footnote_3_132" class="fnanchor">[3]</a></p> + +<div class="figcenter"> +<a name="FIGURE_28"></a> +<a href="images/figure28full.jpg"> + <img src="images/figure28.jpg" alt="Volcanic plateau of Antrim" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 28.</span>—Section across the volcanic plateau of Antrim, from the +Highlands of Inishowen, Co. Donegal, on the N.W., to Belfast Lough +on the S.E., to show the relations of the volcanic rocks to the older +formations.—B. Basaltic sheets breaking off in high escarpments; T. +Trachyte porphyry of Tardree mountain rising from below the newer +plateau-basalts; C. Upper Chalk with flints; N.R. New Red marl and +sandstone (Trias); M. Metamorphic beds of quartzite, various schists +and crystalline limestone; F. Large fault. +</td></tr> +</table> +</div> + +<div class="footnote"><p><a name="Footnote_1_130" id="Footnote_1_130"></a><a href="#FNanchor_1_130"><span class="label">[1]</span></a> Mr. J. Starkie Gardner, from a recent comparison of the plant-remains +of Antrim and Mull, concludes that "that they might belong to +any age between the beginning and the end of the warmer Eocene +period; and that they cannot be of earlier, and are unlikely to be of +later, date."—<i>Trans. Palæont. Soc.</i>, vol. xxxvii. (1883).</p></div> + +<div class="footnote"><p><a name="Footnote_2_131" id="Footnote_2_131"></a><a href="#FNanchor_2_131"><span class="label">[2]</span></a> Having dealt with this district rather fully in <i>The Physical Geology +and Geography of Ireland</i> (Edit. 1891, p. 81), and also in my Presidential +Address (Section C.) at the meeting of the British Association, +1874, a brief review of the subject will be sufficient here, the reader +being referred to the former treatises for fuller details. The following +should also be consulted: Gen. Portlock, <i>Geology of Londonderry and +Tyrone</i> (1843); Sir A. Geikie, "History of Volcanic Action during the +Tertiary Period in the British Isles," <i>Trans. Roy. Soc. Edinburgh</i>, +1888; and the <i>Descriptive Memoirs</i> of the Geological Survey relating +to this tract of country.</p></div> + +<div class="footnote"><p><a name="Footnote_3_132" id="Footnote_3_132"></a><a href="#FNanchor_3_132"><span class="label">[3]</span></a> Owing to the superposition of the basaltic masses on beds of chalk +throughout a long line of coast, we are presented with the curious +spectacle of the whitest rocks in nature overlain by the blackest, as may +be seen in the cliffs at Larne, Glenarm, Kinbane and Portrush. (See +<a href="#FIGURE_27">Fig. 27</a>.)</p></div> +<p><span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_IV_CHAPTER_II" id="PART_IV_CHAPTER_II"></a>CHAPTER II. +<br /><br /> +SUCCESSION OF VOLCANIC ERUPTIONS.</h2> + + +<p>(<i>c.</i>) <i>First Stage.</i>—The earliest eruptions of lava in +the North-east of Ireland belonged to the highly acid +varieties, consisting of quartz-trachyte with tridymite.<a name="FNanchor_1_133" id="FNanchor_1_133"></a><a href="#Footnote_1_133" class="fnanchor">[1]</a> +This rock rises to the surface at Tardree and Brown +Dod hills and Templepatrick. It consists of a light-greyish +felsitic paste enclosing grains of smoke-quartz, +crystals of sanidine, plagioclase and biotite, +with a little magnetite and apatite. It is a rock +of peculiar interest from the fact that it is almost +unique in the British Islands, and has its petrological +counterpart rather amongst the volcanic hills of the +Siebengebirge than elsewhere. It is generally consolidated +with the columnar structure.</p> + +<p><span class="pagenum"><a name="Page_161" id="Page_161">[Pg 161]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_29"> + <img src="images/figure29.jpg" alt="Quarry at Templepatrick" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 29.</span>—Part of the section shown in the quarry at Templepatrick, +showing the superposition of the basalt (<i>d</i>) to the trachyte (<i>b</i>), with the +intervening bed of flint gravel (<i>c</i>). All these rocks are seen to rest +upon an eroded surface of the Chalk formation (<i>a</i>). +</td></tr> +</table> +</div> + +<p>The trachyte appears to have been extruded from +one or more vents in a viscous condition, the principal +vent being probably situated under Tardree mountain, +where the rock occurs in greatest mass, and it probably +arose as a dome-shaped mass, with a somewhat +extended margin, above the floor of Chalk which formed +the surface of the ground.<a name="FNanchor_2_134" id="FNanchor_2_134"></a><a href="#Footnote_2_134" class="fnanchor">[2]</a> (<a href="#FIGURE_27">Fig. 27</a>.) At Templepatrick +the columnar trachyte may be observed +resting on the Chalk, or upon a layer of flint gravel +interposed between the two rocks, and which has been +thrust out of position by a later intrusion of basalt +coming in from the side.<a name="FNanchor_3_135" id="FNanchor_3_135"></a><a href="#Footnote_3_135" class="fnanchor">[3]</a> It is to be observed, +however, that the trachytic lavas nowhere appear +cropping out along with the sheets of basalt around +the escarpments overlooking the sea, or inland; +showing that they did not spread very far from their +<span class="pagenum"><a name="Page_162" id="Page_162">[Pg 162]</a></span>vents of eruption; a fact illustrating the lower +viscosity, or fluidity, of the acid lavas as compared +with those of the basic type.</p> + +<p>(<i>d.</i>) <i>Second Stage.</i>—After an interval, probably of +long duration, a second eruption of volcanic matter +took place over the entire area; but now the acid lavas +of the first stage are replaced by basic lavas. Now, +for the first time, vast masses of basalt and dolerite +are extruded both from vents of eruption and fissures; +and, owing to their extreme viscosity, spread themselves +far and wide until they reach the margin of +some uprising ground of old Palæozoic or Metamorphic +rocks by which the volcanic plain is almost +surrounded. The great lava sheets thus produced +are generally more or less amorphous, vesicular and +amygdaloidal, often exhibiting the globular concentric +structure, and weathering rapidly to a kind of ferruginous +sand or clay under the influence of the atmosphere. +Successive extrusions of these lavas produce +successive beds, which are piled one over the other in +some places to a depth of 600 feet; and at the close +of the stage, when the volcanic forces had for the +time exhausted themselves, the whole of the North-east +of Ireland must have presented an aspect not +unlike that of one of those great tracts of similar +lava in the region of Idaho and the Snake River in +Western America, described in a previous chapter.</p> + +<p>(<i>e.</i>) <i>Third Stage (Inter-volcanic).</i>—The third stage +may be described as inter-volcanic. Owing to the +formation of a basin, probably not deep, and with +gently sloping sides, a large lake was formed over +the centre of the area above described. Its floor was +basalt, and the streams from the surrounding uplands +carried down leaves and stems of trees, strewing them +<span class="pagenum"><a name="Page_163" id="Page_163">[Pg 163]</a></span>over its bed. Occasionally eruptions of ash took place +from small vents, forming the ash-beds with plants +found at Ballypallidy, Glenarm, and along the coast +as at Carrick-a-raide. The streams also brought +down sand and gravel from the uprising domes of +trachyte, and deposited them over the lake-bed along +with the erupted ashes.<a name="FNanchor_4_136" id="FNanchor_4_136"></a><a href="#Footnote_4_136" class="fnanchor">[4]</a> The epoch we are now +referring to was one of economic importance; as, +towards its close, there was an extensive deposition +of pisolitic iron-ore over the floor of the lake, sometimes +to the depth of two or three feet. This ore has +been extensively worked in recent years.</p> + +<div class="figcenter"> +<a name="FIGURE_30"></a> +<a href="images/figure30full.jpg"> + <img src="images/figure30.jpg" alt="Cliffs above the Giant's Causeway" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 30.</span>—Cliff section above the Giant's Causeway, coast of Co. Antrim, showing successive tiers of basaltic +lava, with intervening bands of bole. +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_164" id="Page_164">[Pg 164]</a></span></p><p>(<i>f.</i>) <i>Fourth Stage (Volcanic).</i>—The last stage described +was brought to a termination by a second +outburst of basic lavas on a scale probably even +grander than the preceding. These lavas consisting +of basalt and dolerite, with their varieties, and extruded +from vents and fissures, spread themselves in all +directions over the pre-existing lake deposits or the +older sheets of augitic lava, and probably entirely +buried the trachytic hills. These later sheets solidified +into more solid masses than those of the second +stage. They form successive terraces with columnar +structure, each terrace differing from that above and +below it in the size and length of the columns, and +separated by thin bands of "bole" (decomposed lava), +often reddish in colour, clearly defining the limits of +the successive lava-flows. Nowhere throughout the +entire volcanic area are these successive terraces so +finely laid open to view as along the north coast of +Antrim, where the lofty mural cliffs, worn back into +successive bays with intervening headlands by the +<span class="pagenum"><a name="Page_165" id="Page_165">[Pg 165]</a></span>irresistible force of the Atlantic waves, present to the +spectator a vertical section from 300 to 400 feet in +height, in which the successive tiers of columnar +basalt, separated by thin bands of bole, are seen to +rise one above the other from the water's edge to the +summit of the cliff, as shown in <a href="#FIGURE_30">Fig. 30</a>. Here, also, +at the western extremity of the line of cliffs we find +that remarkable group of vertical basaltic columns, +stretching from the base of the cliff into the Atlantic, +and known far and wide by the name of "The Giant's +Causeway," the upper ends of the columns forming a +tolerably level surface, gently sloping seawards, and +having very much the aspect of an artificial tesselated +pavement on a huge scale. A portion of the Causeway, +with the cliff in the background, is shown in the +figure (<a href="#FIGURE_31">Fig. 31</a>). The columns are remarkable for their +symmetry, being generally hexagonal, though occasionally +they are pentagons, and each column is +horizontally traversed by joints of the ball-and-socket +form, thus dividing them into distinct courses of +natural masonry. These are very well shown in the +accompanying view of the remarkable basaltic pillars +known as "The Chimneys," which stand up from +the margin of the headland adjoining the Causeway, +monuments of past denudation, as they originally +formed individuals amongst the group belonging +to one of the terraces in the adjoining coast.<a name="FNanchor_5_137" id="FNanchor_5_137"></a><a href="#Footnote_5_137" class="fnanchor">[5]</a> +(<a href="#FIGURE_32">Fig. 32</a>).</p> + +<div class="figcenter"> +<a name="FIGURE_31"> + <img src="images/figure31.jpg" alt="The Giant's Causeway" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 31.</span>—The Giant's Causeway, formed of basaltic columns in a +vertical position, and of pentagonal or hexagonal section; above the +Causeway is seen a portion of the cliff composed of tiers of lava with +intervening bands of bole, etc.—(From a photograph.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_166" id="Page_166">[Pg 166]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_32"> + <img src="images/figure32.jpg" alt="The Chimneys" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 32.</span>—"The Chimneys," columns of basalt on slope of cliff overlooking +the Atlantic, north coast of Co. Antrim. The horizontal segments, +or cup-and-ball joints, of the columns are well shown in this +figure. (From a photograph.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_167" id="Page_167">[Pg 167]</a></span></p><p>(<i>g.</i>) <i>Original Thickness of the Antrim Lavas.</i>—It +is impossible to determine with certainty what may +have been the original thickness of the accumulated +sheets of basic lavas with their associated beds of ash +and bole. The greatest known thickness of the lower +zone of lavas is, as I have already stated, about 600 +feet. The intermediate beds of ash and bole sometimes +attain a thickness of 40 feet, and the upper +group of basalt about 400 feet; these together would +constitute a series of over 1,000 feet in thickness. But +this amount, great as it is, is undoubtedly below the +original maximum, as the uppermost sheets have been +removed by denuding agencies, we know not to what +extent. Nor is it of any great importance. Sufficient +remains to enable us to form a just conception +of the magnitude both as regards thickness and extent +of the erupted matter of the Miocene period over the +North-east of Ireland and adjoining submerged tracts, +and of the magnitude of the volcanic operations necessary +for the production of such masses.</p> + +<p><span class="pagenum"><a name="Page_168" id="Page_168">[Pg 168]</a></span></p><p>(<i>h.</i>) <i>Volcanic Necks.</i>—As already remarked, no +craters of eruption survive throughout the volcanic +region of the North-east of Ireland, owing to the +enormous extent of the denudation which this region +has undergone since the Miocene Epoch; but the old +"necks" of such craters—in other words, the pipes +filled with either solid basalt, or basalt and ashes—are +still to be found at intervals over the whole area. +Owing to the greater solidity of the lava which filled +up these "necks" over the plateau-basaltic sheets +which surround them, they appear as bosses or hills +rising above the general level of the ground. One of +these bosses of highly columnar basalt occurs between +Portrush and Bushmills, not far from Dunluce Castle, +another at Scawt Hill, near Glenarm, and a third at +Carmoney Hill above Belfast Lough. But by far +the most prominent of these old solidified vents of +eruption is that of Sleamish, a conspicuous mountain +which rises above the general level of the plateau +near Ballymena, and attains an elevation of 1,437 feet +above the sea. Seen from the west, the mountain +has the appearance of a round-topped cone; but on +examination it is found to be in reality a huge dyke, +breaking off abruptly towards the north-west, in which +direction it reaches its greatest height, then sloping +downwards towards the east. This form suggests +that Sleamish is in reality one of the fissure-vents +of eruption rather than the neck of an old volcano. +The rock of which it is formed consists of exceedingly +massive, coarsely-crystalline dolerite, rich in olivine, +and divided into large quadrangular blocks by parallel +joint planes. Its junction with the plateau-basalt +from which it rises can nowhere be seen; but at the +nearest point where the two rocks are traceable the +<span class="pagenum"><a name="Page_169" id="Page_169">[Pg 169]</a></span>plateau-basalt appears to be somewhat indurated; +breaking with a splintery fracture and a sharp ring +under the hammer, suggesting that the lava of +Sleamish had been extruded through the horizontal +sheets, and had considerably indurated the portions in +contact with, or in proximity to, it.<a name="FNanchor_6_138" id="FNanchor_6_138"></a><a href="#Footnote_6_138" class="fnanchor">[6]</a> Amongst the +vents filled with ash and agglomerate, the most remarkable +is that of Carrick-a-raide, near Ballycastle. +It forms this rocky island and a portion of the adjoining +coast, where the beds of ash are finely displayed; +consisting of fragments and bombs of basalt, with +pieces of chalk, flint, and peperino, which is irregularly +bedded. These ash-beds attain a thickness of about +120 feet just below the road to Ballycastle, but rapidly +tail out in both directions from the locality of the +vent. Just below the ash-beds, the white chalk with +flints may be seen extending down into the sea-bed. +Nowhere in Antrim is there such a display of volcanic +ash and agglomerate as at this spot.<a name="FNanchor_7_139" id="FNanchor_7_139"></a><a href="#Footnote_7_139" class="fnanchor">[7]</a></p> + +<p>(<i>i.</i>) <i>Dykes: Conditions under which they were +Erupted.</i>—No one can visit the geological sections +in Co. Antrim and the adjoining districts of Down, +Armagh, Derry, and Tyrone, without being struck by +the great number and variety of the igneous dykes +by which the rocks are traversed. The great majority +of these dykes are basaltic, and they are found traversing +all the formations, including the Cretaceous and +Tertiary basaltic sheets. The Carlingford and Mourne +Mountains are seamed with such dykes, and they are +<span class="pagenum"><a name="Page_170" id="Page_170">[Pg 170]</a></span>splendidly laid open to view along the coast south +of Newcastle in Co. Down, as also along the Antrim +coast from Belfast to Larne. The fine old castle of +Carrickfergus has its foundations on one of those dyke-like +intrusions, but one of greater size than ordinary. +All the dykes here referred to are not, however, of +the same age, as is conclusively proved by sections +amongst the Mourne Mountains where cliffs of Lower +Silurian strata, superimposed on the intrusive granite +of the district, exhibit two sets of basaltic dykes—one +(the older) abruptly terminated at the granite margin, +the other and newer penetrating the granite and Silurian +rocks alike. It is not improbable that the older +dykes belong to the Carboniferous or Permian age, +while the newer are with equal probability of Tertiary +age. Sir A. Geikie has shown that the Tertiary dykes +of the North of Ireland are representatives of others +occurring at intervals over the North of England, +and Central and Western Scotland, all pointing towards +the central region of volcanic activity; or in a parallel +direction thereto, approximating to the N.W. in +Ireland, the Island of Islay, and East Argyleshire, +but in the centre of Scotland generally ranging from +east to west.<a name="FNanchor_8_140" id="FNanchor_8_140"></a><a href="#Footnote_8_140" class="fnanchor">[8]</a> The area affected by the dykes of undoubted +Tertiary age Geikie estimates at no less than +40,000 square miles—a territory greater than either +Scotland or Ireland, and equal to more than a third +of the total land-surface of the British Isles;<a name="FNanchor_9_141" id="FNanchor_9_141"></a><a href="#Footnote_9_141" class="fnanchor">[9]</a> and he +regards them as posterior "to the rest of the geological +structures of the regions which they traverse." +<span class="pagenum"><a name="Page_171" id="Page_171">[Pg 171]</a></span>It is clear that the dykes referred to belong to one +great system of eruption or intrusion; and they may +be regarded as the manifestation of the final effort of +internal forces over this region of the British Isles. +They testify to the existence of a continuous <i>magma</i> +(or shell) of augitic lava beneath the crust; and as +the aggregate horizontal extent of all these dykes, or +of the fissures which they fill, must be very considerable, +it is clear that the crust through which they +have been extruded has received an accession of +horizontal space, and has been fissured by forces +acting from beneath, as the late Mr. Hopkins, of +Cambridge, had explained on mechanical grounds in +his elaborate essay many years ago.<a name="FNanchor_10_142" id="FNanchor_10_142"></a><a href="#Footnote_10_142" class="fnanchor">[10]</a> This view +occurred to myself when examining the region of the +North-east of Ireland, but I was not then aware that it +had been dealt with on mathematical principles by so +eminent a mathematician. The bulging of the crust +is a necessary consequence of the absence of plication +of the strata due to the extrusion of this enormous +quantity of molten lava; and the intrusion of +thousands of dykes over the North-east of Ireland, +unaccompanied by foldings of the strata, must have +added a horizontal space of several thousand feet to +that region.<a name="FNanchor_11_143" id="FNanchor_11_143"></a><a href="#Footnote_11_143" class="fnanchor">[11]</a></p> + +<div class="footnote"><p><a name="Footnote_1_133" id="Footnote_1_133"></a><a href="#FNanchor_1_133"><span class="label">[1]</span></a> A peculiar form of crystalline quartz first recognized in this rock by +a distinguished German petrologist, the late Prof. A. von Lasaulx, who +visited the district in 1876.</p></div> + +<div class="footnote"><p><a name="Footnote_2_134" id="Footnote_2_134"></a><a href="#FNanchor_2_134"><span class="label">[2]</span></a> Sir A. Geikie has disputed the correctness of the view, which I advocated +as far back as 1874, that the trachytic lavas of Antrim are the earliest +products of volcanic action; but at the time he wrote his paper on the +volcanic history of these islands, it was not known that pebbles of this +trachyte are largely distributed amongst the ash-beds which occur in the +very midst of the overlying basaltic sheets, as I shall have to explain +later on. This discovery puts the question at rest as regards the +relations of the two sets of rocks.</p></div> + +<div class="footnote"><p><a name="Footnote_3_135" id="Footnote_3_135"></a><a href="#FNanchor_3_135"><span class="label">[3]</span></a> This remarkable section at the chalk quarries of Templepatrick the +author has figured and described in the <i>Physical Geology and Geography +of Ireland</i>, p. 99, 2nd edit. (1891), where the reader will find the subject +discussed more fully than can be done here.</p></div> + +<div class="footnote"><p><a name="Footnote_4_136" id="Footnote_4_136"></a><a href="#FNanchor_4_136"><span class="label">[4]</span></a> These pebbles were first noticed by Mr. McHenry, of the Irish +Geological Survey, in 1890.</p></div> + +<div class="footnote"><p><a name="Footnote_5_137" id="Footnote_5_137"></a><a href="#FNanchor_5_137"><span class="label">[5]</span></a> The vertical position of the columns of the Giant's Causeway is +rather enigmatical. The Causeway cannot be a dyke, as has often been +supposed, otherwise the columns would have been horizontal, <i>i.e.</i>, at +right angles to the sides of the dyke. Mr. R. G. Symes, of the Geological +Survey, has suggested that the Causeway columns have been +vertically lowered between two lines of fault, and that originally they +formed a portion of the tier of beautiful columns seen in the cliff above, +and known as "The Organ."</p></div> + +<div class="footnote"><p><a name="Footnote_6_138" id="Footnote_6_138"></a><a href="#FNanchor_6_138"><span class="label">[6]</span></a> Sleamish and several other of the Antrim vents are described by Sir +A. Geikie in the monograph already referred to, <i>loc. cit.</i>, p. 101, <i>et seq.</i> +Also in the <i>Expl. Memoirs of the Geological Survey of Ireland</i>.</p></div> + +<div class="footnote"><p><a name="Footnote_7_139" id="Footnote_7_139"></a><a href="#FNanchor_7_139"><span class="label">[7]</span></a> A diagrammatised section of the Carrick-a-raide volcanic neck is +given by Sir A. Geikie, <i>loc. cit.</i>, p. 105.</p></div> + +<div class="footnote"><p><a name="Footnote_8_140" id="Footnote_8_140"></a><a href="#FNanchor_8_140"><span class="label">[8]</span></a> Geikie, <i>loc. cit.</i>, p. 29, <i>et seq.</i></p></div> + +<div class="footnote"><p><a name="Footnote_9_141" id="Footnote_9_141"></a><a href="#FNanchor_9_141"><span class="label">[9]</span></a> P. 32. The view that the crust of the earth has been horizontally +extended by the intrusion of dykes is noticed by McCulloch in reference +to the dykes of Skye.</p></div> + +<div class="footnote"><p><a name="Footnote_10_142" id="Footnote_10_142"></a><a href="#FNanchor_10_142"><span class="label">[10]</span></a> Hopkins, <i>Cambridge Phil. Trans.</i>, vol. vi. p. 1 (1836).</p></div> + +<div class="footnote"><p><a name="Footnote_11_143" id="Footnote_11_143"></a><a href="#FNanchor_11_143"><span class="label">[11]</span></a> As suggested in my Presidential Address to Section C. of the British +Association at Belfast, 1874.</p></div> +<p><span class="pagenum"><a name="Page_172" id="Page_172">[Pg 172]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_IV_CHAPTER_III" id="PART_IV_CHAPTER_III"></a>CHAPTER III. +<br /><br /> +ISLAND OF MULL AND ADJOINING COAST.</h2> + + +<p>The Island of Mull, with the adjoining districts of +Morvern and Ardnamurchan, forms the more southern +of the two chief centres of Tertiary volcanic eruptions +in the West of Scotland, that of Skye being the more +northern. These districts have been the subject of +critical and detailed study by several geologists, from +McCulloch down to the present day; and amongst +the more recent, Sir Archibald Geikie and Professor +Judd hold the chief place. Unfortunately, the interpretation +of the volcanic phenomena by these two +accomplished observers has led them to very different +conclusions as regards several important points in the +volcanic history of these groups of islands; as, for +example, regarding the relative ages of the plateau-basalts +and the acid rocks, such as the trachytes and +granophyres; again as regards the presence of distinct +centres of eruption; and also as regards the relations +of the gabbros of Skye to the basaltic sheets. Such +being the case, it would appear the height of rashness +on the part of the writer, especially in the absence of +a detailed examination of the sections over the whole +region, to venture on a statement of opinion regarding +the points at issue; and he must, therefore, content +himself with a brief account of the phenomena as +<span class="pagenum"><a name="Page_173" id="Page_173">[Pg 173]</a></span>gathered from a perusal of the writings of these and +other observers,<a name="FNanchor_1_144" id="FNanchor_1_144"></a><a href="#Footnote_1_144" class="fnanchor">[1]</a> guided also to some extent by the +analogous phenomena presented by the volcanic +region of the North-east of Ireland.</p> + +<p>(<i>a.</i>) <i>General Features.</i>—As in the case of the +Antrim district, the Island of Mull and adjoining +tracts present us with the spectacle of a vast accumulation +of basaltic lava-flows, piled layer upon layer, +with intervening beds of bole and tuff, up to a thickness, +according to Geikie, of about 3,500 feet. At the +grand headland of Gribon, on the west coast, the +basaltic sheets are seen to rise in one sheer sweep to +a height of 1,600 feet, and then to stretch away with +a slight easterly dip under Ben More at a distance of +some eight miles. This mountain, the upper part of +which is formed of beds of ashes, reaches an elevation +of 3,169 feet, so that the accumulated thickness of the +beds of basalt under the higher part of the mountain +must be at least equal to the amount stated above—that +is, twice as great as the representative masses of +Antrim. The base of the volcanic series is seen at +Carsaig and Gribon to rest on Cretaceous and +Jurassic rocks, like those of Antrim; hence the +Tertiary age is fully established by the evidence of +superposition. This was further confirmed by the +discovery by the Duke of Argyll,<a name="FNanchor_2_145" id="FNanchor_2_145"></a><a href="#Footnote_2_145" class="fnanchor">[2]</a> some years ago +(1850), of bands of flint-gravel and tuff, with dicotyledonous +leaves amongst the basalts of Ardtun Head. +<span class="pagenum"><a name="Page_174" id="Page_174">[Pg 174]</a></span>The basement beds of tuff and gravel contain, besides +pebbles of flint and chalk, others of sanidine trachyte, +showing that highly acid lavas had been extruded +and consolidated before the first eruption of the +plateau-basalts; another point of analogy between the +volcanic phenomenon of Antrim and the Inner Hebrides. +These great sheets of augitic lava extend +over the whole of the northern tract of Mull, the +Isles of Ulva and Staffa, and for a distance of several +miles inwards from the northern shore of the Sound +of Mull, covering the wild moorlands of Morvern and +Ardnamurchan, where they terminate in escarpments +and outlying masses, indicating an originally much +more extended range than at the present day. The +summits of Ben More and its neighbouring height, +Ben Buy, are formed of beds of ash and tuff. The +volcanic plateau is, according to Judd, abruptly +terminated along the southern side by a large vault, +bringing the basalt in contact with Palæozoic rocks.<a name="FNanchor_3_146" id="FNanchor_3_146"></a><a href="#Footnote_3_146" class="fnanchor">[3]</a></p> + +<p>(<i>b.</i>) <i>Granophyres.</i>—The greater part of the tract +lying to the south of Loch na Keal, which almost +divides Mull into two islands, and extending southwards +and eastwards to the shores of the Firth of +Lorn and the Sound of Mull, is formed of a peculiar +group of acid (or highly silicated) rocks, classed under +the general term of "Granophyres." These rocks +approach towards true granites in one direction, and +through quartz-porphyry and felsite to rhyolite in +another—probably depending upon the conditions of +cooling and consolidation. In their mode of weathering +and general appearance on a large scale, they +present a marked contrast to the basic lavas with +which they are in contact from the coast of L. na +<span class="pagenum"><a name="Page_175" id="Page_175">[Pg 175]</a></span>Keal to that of L. Buy. The nature of this contact, +whether indicating the priority of the granophyres to +the plateau-basalts or otherwise, is a matter of dispute +between the two observers above named; but the +circumstantial account given by Sir A. Geikie,<a name="FNanchor_4_147" id="FNanchor_4_147"></a><a href="#Footnote_4_147" class="fnanchor">[4]</a> accompanied +by drawings of special sections showing +this contact, appears to prove that the granophyre is +the newer of the two masses of volcanic rock, and +that it has been intruded amongst the basaltic-lavas +at a late period in the volcanic history of these islands. +A copy of one of these sketches is here given (<a href="#FIGURE_33">Fig. 33</a>), +according to which the felsite is shown to penetrate +the basaltic sheets at Alt na Searmoin in Mull; other +sections seen at Cruach Torr an Lochain, and on the +south side of Beinn Fada, appear to lead to similar +conclusions. These rocks are penetrated by numerous +basaltic dykes.</p> + +<div class="figcenter"> +<a name="FIGURE_33"> + <img src="images/figure33.jpg" alt="Alt na Searmoin" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 33.</span>—Section at Alt na Searmoin, Mull, to show the intrusion +of felsite (or granophyre) (<i>b</i>) into basalt and dolerite (<i>a</i>) of the plateau-basalt +series.—(Geikie.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_176" id="Page_176">[Pg 176]</a></span></p><p>(<i>c.</i>) <i>Representative Rocks of Mourne and Carlingford, +Ireland.</i>—Assuming Sir A. Geikie's view to be +correct, it is possible that we may have in the granite +and quartz-porphyries of Mourne and Carlingford +representatives of the granites, granophyres, and other +acid rocks of the later period of Mull. The granite of +Mourne is peculiar in structure, and differs from the +ordinary type of that rock in which the silica forms +the ground mass. In the case of the granite of the +Mourne Mountains, the rock consists of a crystalline +granular aggregate of orthoclase, albite, smoke-quartz, +and mica; it is also full of drusy cavities, in which the +various minerals crystallise out in very perfect form. +As far as regards direct evidence, the age of this rock +can only be stated to be post-Carboniferous, and earlier +than certain Tertiary basaltic dykes by which it is +traversed. The granophyres of Mull are traversed by +similar dykes, which are representatives of the very +latest stage of volcanic action in the British Islands. +The author is therefore inclined to concur with Sir +A. Geikie in assigning to the granite of the Mourne +Mountains, and the representative felsitic rocks of the +Carlingford Mountains, a Tertiary age—in which case +the analogy between the volcanic phenomena of the +Inner Hebrides and of the North-east of Ireland would +seem to be complete.<a name="FNanchor_5_148" id="FNanchor_5_148"></a><a href="#Footnote_5_148" class="fnanchor">[5]</a></p> + +<div class="footnote"><p><a name="Footnote_1_144" id="Footnote_1_144"></a><a href="#FNanchor_1_144"><span class="label">[1]</span></a> Geikie, <i>Proc. Roy. Soc. Edinburgh</i> (1867); <i>Brit. Assoc. Rep.</i> +(Dundee, 1867); "Tertiary Volcanic Rocks of the British Isles," +<i>Quart. Journ. Geol. Soc.</i>, vol. xxvii. p. 279; also, "History of Volcanic +Action in British Isles," <i>Trans. Roy. Soc. Edin.</i> (1888); Judd, "On +the Ancient Volcanoes of the Highlands," etc., <i>Quart. Journ. Geol. Soc.</i>, +vol. xxx. p. 233; and <i>Volcanoes</i>, p. 139.</p></div> + +<div class="footnote"><p><a name="Footnote_2_145" id="Footnote_2_145"></a><a href="#FNanchor_2_145"><span class="label">[2]</span></a> <i>Brit. Assoc. Rep.</i> for 1850, p. 70.</p></div> + +<div class="footnote"><p><a name="Footnote_3_146" id="Footnote_3_146"></a><a href="#FNanchor_3_146"><span class="label">[3]</span></a> Judd, <i>Quart. Jour. Geol. Soc.</i>, vol. xxx. p. 242.</p></div> + +<div class="footnote"><p><a name="Footnote_4_147" id="Footnote_4_147"></a><a href="#FNanchor_4_147"><span class="label">[4]</span></a> <i>History of Volcanic Action, etc.</i>, <i>loc. cit.</i> p. 153, <i>et seq.</i> The +"Granophyres" of Geikie come under the head of "Felsites," passing +into "granite" in one direction and quartz-trachyte in another, according +to Judd; the proportion of silica from 69 to 75 per cent.—<i>Quart. +Jour. Geol. Soc.</i>, vol. xxx. p. 235.</p></div> + +<div class="footnote"><p><a name="Footnote_5_148" id="Footnote_5_148"></a><a href="#FNanchor_5_148"><span class="label">[5]</span></a> This view the author has expressed in a recent edition of <i>The +Physical Geology of Ireland</i>, p. 177 (1891).</p></div> +<p><span class="pagenum"><a name="Page_177" id="Page_177">[Pg 177]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_IV_CHAPTER_IV" id="PART_IV_CHAPTER_IV"></a>CHAPTER IV. +<br /><br /> +ISLE OF SKYE.</h2> + + +<p>This is the largest and most important of all the +Tertiary volcanic districts, but owing to the extensive +denudation to which, in common with other Tertiary +volcanic regions of the British Isles, it has been subjected, +its present limits are very restricted comparatively +to its original extent. Not only is this evident +from the manner in which the basaltic sheets terminate +along the sea-coast in grand mural cliffs, as opposite +"Macleod's Maidens," and at the entrance to Lough +Bracadale on the western coast, but the evidence is, +according to Sir A. Geikie, still more striking along the +eastern coast; showing that the Jurassic, and other older +rocks there visible, were originally buried deep under +the basaltic sheets which have been stripped from off +that part of the country. These great plateau-basalts +occupy about three-fourths of the entire island along +the western and northern areas, rising into terraced +mountains over 2,000 feet in height, and are deeply +furrowed by glens and arms of the sea, along which the +general structure of the tableland is laid open, sometimes +for leagues at a time.</p> + +<p>It is towards the south-eastern part of the island +that the most interesting and important phenomena +are centred; for here we meet with representatives +<span class="pagenum"><a name="Page_178" id="Page_178">[Pg 178]</a></span>of the acid (or highly silicated) group of rocks, and of +remarkable beds of gabbro, which have long attracted +the attention of petrologists. These latter beds, +throughout a considerable distance round the flanks +of the Cuillin Hills, are interposed between the acid +rocks and the plateau-basalts; but towards the north, +on approaching Lough Sligahan, the acid rocks, consisting +of granophyres, quartz-porphyries, and hornblendic-granitites, +are in direct contact with the +plateau-basalts; and, according to the very circumstantial +account of Sir A. Geikie, are intrusive into +them; not only sending veins into the basaltic sheets, +but also producing a marked alteration in their structure +where they approach the newer intrusive mass. +Equally circumstantial is the same author's account of +the relations of the granophyres to the gabbros,<a name="FNanchor_1_149" id="FNanchor_1_149"></a><a href="#Footnote_1_149" class="fnanchor">[1]</a> as seen +at Meall Dearg and the western border of the Cuillin +Hills—where the former rock may be seen to send +numerous veins into the latter. Not only is this so, +but the granophyre is frequently seen to truncate, +and abruptly terminate some of the basaltic dykes by +which the basic sheets are traversed—as in the neighbourhood +of Beinn na Dubhaic. All these phenomena +strongly remind us of the conditions of similar rocks +amongst the mountains of Mourne and Carlingford in +Ireland; where, at Barnaveve, the syenite (or hornblendic +quartz-felsite) is seen to break through the +masses of olivine gabbro, and send numerous veins +into this latter rock.<a name="FNanchor_2_150" id="FNanchor_2_150"></a><a href="#Footnote_2_150" class="fnanchor">[2]</a></p> + +<p>The interpretation here briefly sketched differs +<span class="pagenum"><a name="Page_179" id="Page_179">[Pg 179]</a></span>widely from that arrived at by Professor Judd. The +granitoid masses of the Red Mountains (Beinn Dearg) +and the neighbouring heights are, in his view, the +roots of the great volcano from which were erupted +the various lavas; the earlier eruptions producing +the acid lavas, to be followed by the gabbros, and +these by the plateau-basaltic sheets, which stretch +away towards the north and west into several peninsulas. +Thus he holds that "the rocks of basic composition +were ejected subsequently to those of the +acid variety," and appeals to various sections in confirmation +of this view.<a name="FNanchor_3_151" id="FNanchor_3_151"></a><a href="#Footnote_3_151" class="fnanchor">[3]</a> To reconcile these views is +at present impossible; but as the controversy between +these two observers is probably not yet closed, there +is room for hope that the true interpretation of the +relations of these rocks to each other will ere long +be fully established.</p> + +<div class="footnote"><p><a name="Footnote_1_149" id="Footnote_1_149"></a><a href="#FNanchor_1_149"><span class="label">[1]</span></a> Geikie, <i>loc. cit.</i>, p. 161, etc.</p></div> + +<div class="footnote"><p><a name="Footnote_2_150" id="Footnote_2_150"></a><a href="#FNanchor_2_150"><span class="label">[2]</span></a> <i>Physical Geology of Ireland</i>, 2nd edition, p. 174 (Fig. 21). +Professor Judd has also come to the conclusion that the granite of +Mourne is of Tertiary age, <i>Quart. Jour. Geol. Soc.</i>, vol. xxx. p. 275.</p></div> + +<div class="footnote"><p><a name="Footnote_3_151" id="Footnote_3_151"></a><a href="#FNanchor_3_151"><span class="label">[3]</span></a> Judd, <i>loc. cit.</i>, p. 254.</p></div> +<p><span class="pagenum"><a name="Page_180" id="Page_180">[Pg 180]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_IV_CHAPTER_V" id="PART_IV_CHAPTER_V"></a>CHAPTER V. +<br /><br /> +THE SCUIR OF EIGG.</h2> + + +<p>Amongst the more remarkable of the smaller islets +are those of Eigg, Rum, Canna, and Muck, lying between +Mull on the south and Skye on the north, and +undoubtedly at one time physically connected together. +The Island of Eigg is especially remarkable +for the fact, as stated by Geikie, that here we have +the one solitary case of "a true superficial stream of +acid lava—that of the Scuir of Eigg."<a name="FNanchor_1_152" id="FNanchor_1_152"></a><a href="#Footnote_1_152" class="fnanchor">[1]</a> (<a href="#FIGURE_34">Fig. 34</a>.) +This forms a sinuous ridge, composed of pitchstone +of several kinds, of over two miles in length, rising +from the midst of a tableland of bedded basalt and +tuff to a height of 1,289 feet above the ocean; the +plateau-basalt is traversed by basaltic dykes, ranging +in a N.W.-S.E. direction. But what is specially remarkable +is the evidence afforded by an examination +of the course of the Scuir, that it follows the channel +of an ancient river-valley, which has been hollowed +out in the surface of the plateau. The course of this +channel is indicated by the presence of a deposit of +river-gravel, which in some places forms a sort of +cushion between the base of the Scuir and the side of +the channel. Over this gravel-bed the viscous pitchstone-lava +appears to have flowed, taking possession +<span class="pagenum"><a name="Page_181" id="Page_181">[Pg 181]</a></span>of the river-channel, and also of the beds of several +small tributary streams which flowed into the channel +of the Scuir. The recent date of the pitchstone forming +this remarkable mural ridge, once occupying the bed of +a river-channel, is shown by the fact that the basaltic +dykes which traverse the plateau-basalts are truncated +by the river-gravel, which is, therefore, more recent; +and, as we have seen, the pitchstone stream is more +recent than the river-gravel. But at the time when +this last volcanic eruption took place, the physical +geography of the whole region must have been very +different from that of the present time. From the +character and composition of the pebbles in the old +river-bed, amongst which are Cambrian sandstone, +quartzite, clay-slate, and white Jurassic limestone, +Sir A. Geikie concludes that when the river was +flowing, the island must have been connected with +the mainland to the east where the parent masses +of these pebbles are found.</p> + +<div class="figcenter"> +<a name="FIGURE_34"> + <img src="images/figure34.jpg" alt="Scuir of Eigg" style="margin-left:36px;" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 34.</span>—View of the Scuir of Eigg from the east. The lower +portion of the mountain is formed of bedded basalt, or dolerite with +numerous dykes and veins of basalt, felstone, and pitchstone; the upper +cliff, or Scuir, is composed of pitchstone of newer age, the remnant of a +lava flow which once filled a river channel in the basaltic sheets. A +dyke, or sheet, of porphyry is seen to be interposed between the Scuir +and the basaltic sheets.—(After Geikie.) +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_182" id="Page_182">[Pg 182]</a></span></p><p><i>Effects of Denudation.</i>—The position of the Scuir +of Eigg and its relations to the basaltic sheets show +the enormous amount of denudation which these +latter have undergone since the stream of pitchstone-lava +filled the old river channel. The walls, or banks, +of the channel have been denuded away, thus converting +the pitchstone casting into a projecting wall +of rock. That it originally extended outwards into +the ocean to a far greater distance than at present is +evident from the abruptly truncated face of the cliff; +and yet this remarkable volcanic mass seems to have +been, perhaps, the most recent exhibition of volcanic +action to be found in the British Isles. It is perhaps, +on this account, the most striking of the numerous +examples exhibited throughout the West of Scotland +and the North-east of Ireland of the enormous amount +of denudation to which these districts have been subjected +since the extinction of the volcanic fires; and +this at a period to which we cannot assign a date +more ancient than that of the Pliocene. Yet, let us +consider for a moment to what physical vicissitudes +these districts have been subjected since that epoch. +Assuming, as we may with confidence, that the volcanic +eruptions were subaërial, and that the tracts +covered by the plateau-basalts were in the condition +of dry land when the eruptions commenced, in this +<span class="pagenum"><a name="Page_183" id="Page_183">[Pg 183]</a></span>condition they continued in the main throughout the +period of volcanic activity. But the eruptions had +scarcely ceased, and the lava floods and dykes become +consolidated, before the succeeding glacial epoch +set in; when the snows and glaciers of the Scottish +Highlands gradually descending from their original +mountain heights, and spreading outwards in all +directions, ultimately enveloped the whole of the +region we are now considering until it was entirely +concealed beneath a mantle of ice moving slowly, +but irresistibly, outwards towards the Atlantic, crossing +the deep channels, such as the Sound of Mull and +the Minch, climbing up the sides of opposing rocks +and islands until even the Outer Hebrides and the +North-east of Ireland were covered by one vast +mantle of ice and snow. The movement of such a +body of ice over the land must have been attended +with a large amount of abrasion of the rocky floor; +nor have the evidences of that abrasion entirely disappeared +even at the present day. We still detect +the grooves and scorings on the rock-surfaces where +they have been protected by a coating of boulder +clay; and we still find the surface strewn with the +blocks and <i>débris</i> of that mighty ice-flood.</p> + +<p>But whatever may have been the amount of erosion +caused by the great ice-sheet, it was chiefly confined +to the more or less horizontal surface-planes. Erosion +of another kind was to succeed, and to produce more +lasting effects on the configuration of the surface. On +the disappearance of the ice-sheet, an epoch characterised +by milder conditions of climate set in. This +was accompanied by subsidence and submersion of +large tracts of the land during the Interglacial stage; +so that the sea rose to heights of several hundred feet +<span class="pagenum"><a name="Page_184" id="Page_184">[Pg 184]</a></span>above the present level, and has left behind stratified +gravels with shells at these elevations in protected +places. During this period of depression and of subsequent +re-emergence the wave-action of the Atlantic +waters must have told severely on the coast and islands, +wearing them into cliffs and escarpments, furrowing +out channels and levelling obstructions. Such action +has gone on down to the present day. The North-west +of Scotland and of Ireland has been subjected +throughout a very lengthened period to the wear and +tear of the Atlantic billows. In the case of the former, +the remarkable breakwater which nature has thrown +athwart the North-west Highlands in the direction of +the waves, forming the chain of islands constituting +the Outer Hebrides, and composed of very tough +Archæan gneiss and schist, has done much to retard the +inroads which the waves might otherwise have made +on the Isle of Skye; while Coll and Tiree, composed +of similar materials, have acted with similar beneficent +effect for Mull and the adjoining coasts. But such is +the tremendous power of the Atlantic billows when +impelled by westerly winds, that to their agency must +be mainly attributed the small size of the volcanic +land-surfaces as compared with their original extent, +and the formation of those grand headlands which +are presented by the igneous masses of Skye, Ardnamurchan, +and Mull towards the west. Rain and river +action, supplemented by that of glaciers, have also +had a share in eroding channels and wearing down +the upper surface of the ground, with the result we at +present behold in the wild and broken scenery of the +Inner Hebrides and adjoining coast.</p> + +<div class="footnote"><p><a name="Footnote_1_152" id="Footnote_1_152"></a><a href="#FNanchor_1_152"><span class="label">[1]</span></a> Geikie, <i>loc. cit.</i>, p. 178; also <i>Quart. Jour. Geol. Soc.</i>, vol. xxvii. +p. 303.</p></div> +<p><span class="pagenum"><a name="Page_185" id="Page_185">[Pg 185]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_IV_CHAPTER_VI" id="PART_IV_CHAPTER_VI"></a>CHAPTER VI. +<br /><br /> +ISLE OF STAFFA.</h2> + + +<p>Reference has been made to this remarkable island +in a former page, but some more extended notice is +desirable before leaving the region of the Inner +Hebrides. Along with the islands of Pladda, Treshnish, +and Blackmore, Staffa is one of the outlying +volcanic islands of the group, being distant about six +miles from the coast of Mull, and indicates the minimum +distance to which the plateau-basaltic sheets +originally extended in the direction of the old marginal +lands of Tiree and Coll. The island consists of successive +sheets of bedded basaltic lava, with partings +of tuff, one of which of considerable thickness is shown +to lie at the base of the cliff on the south-west side of +the island.<a name="FNanchor_1_153" id="FNanchor_1_153"></a><a href="#Footnote_1_153" class="fnanchor">[1]</a> The successive lava-sheets present great +varieties of structure, like those on the north coast of +Antrim; some being amorphous, others columnar, +with either straight or bent columns. The lava-sheet +out of which Fingal's Cave is excavated consists of +vertical prisms, beautifully formed, and surmounted +by an amorphous mass of the same material. At the +entrance of the Boat Cave we have a somewhat similar +<span class="pagenum"><a name="Page_186" id="Page_186">[Pg 186]</a></span>arrangement of the columns;<a name="FNanchor_2_154" id="FNanchor_2_154"></a><a href="#Footnote_2_154" class="fnanchor">[2]</a> but at the Clam-shell +Cave the prisms are curved, indicating some movement +in the viscous mass before they had been fully +consolidated.</p> + +<p>Fingal's Cave is called after the celebrated prince +of Morvern (or Morven), a province of ancient Caledonia. +He is supposed to have been the father of +Ossian, the Celtic bard rendered famous by Macpherson. +The cave, one of many which pierce the coast-cliffs +of Western Scotland, is 227 feet in length, +166 feet in height, and 40 feet in width. On all sides +regular columns of basalt, some entire, others broken, +rise out of the water and support the roof. The cave +is only accessible in calm weather.</p> + +<div class="footnote"><p><a name="Footnote_1_153" id="Footnote_1_153"></a><a href="#FNanchor_1_153"><span class="label">[1]</span></a> A drawing of this cliff is given by Geikie in the <i>Manual of Geology</i> +(Jukes and Geikie), 3rd edition, p. 277.</p></div> + +<div class="footnote"><p><a name="Footnote_2_154" id="Footnote_2_154"></a><a href="#FNanchor_2_154"><span class="label">[2]</span></a> Prestwich, <i>Geology</i>, vol. i. p. 281, where a view of this cave is +given.</p></div> +<p><span class="pagenum"><a name="Page_187" id="Page_187">[Pg 187]</a></span></p> + + +<hr class="major" /> +<h1><a name="PART_V" id="PART_V"></a>PART V. +<br /><br /> +PRE-TERTIARY VOLCANIC ROCKS.</h1> + + + +<hr class="major" /> +<h2><a name="PART_V_CHAPTER_I" id="PART_V_CHAPTER_I"></a>CHAPTER I. +<br /><br /> +THE DECCAN TRAP-SERIES OF INDIA.</h2> + + +<p>The great outpourings of augitic lava of Tertiary and +recent times which we have been considering appear +to have been anticipated in several parts of the world, +more especially in Peninsular India and in Africa, +and it is desirable that we should devote a few pages +to the description of these remarkable volcanic formations, +as they resemble, both in their mode of +occurrence and general structure, some of the great +lava-floods of a more recent period we have been considering. +Of the districts to be described, the first +which claims our notice is the Deccan.</p> + +<p>(<i>a.</i>) <i>Extent of the Volcanic Plateau.</i>—The volcanic +plateau of the Deccan stretches from the borders of +the Western Ghats and the sea-coast near Bombay +inland to Amarantak, at the head of the Narbudda +River (long. 82° E.), and from Belgaum (lat. 15° 31' N.) +to near Goona (lat. 24° 30'). The vast area thus +circumscribed is far from representing the original +extent of the tract overspread by the lava-floods, as +outlying fragments of these lavas are found as far +east as long. 84° E. in one direction, and at Kattiwar +<span class="pagenum"><a name="Page_188" id="Page_188">[Pg 188]</a></span>and Cutch in another. The present area, however, is +estimated to be not less than 200,000 square miles.<a name="FNanchor_1_155" id="FNanchor_1_155"></a><a href="#Footnote_1_155" class="fnanchor">[1]</a></p> + +<p>(<i>b.</i>) <i>Nature and Thickness of the Lava-flows.</i>—This +tract is overspread almost continuously by sheets of +basaltic lava, with occasional bands of fresh-water strata +containing numerous shells, figured and described by +Hislop, and believed by him to be of Lower Eocene +age. The lava-sheets vary considerably in character, +ranging from finest compact basalt to coarsely +crystalline dolerite, in which olivine is abundant. +The columnar structure is not prevalent, the rock +being either amorphous, or weathering into concentric +shells. Volcanic ash, or bole, is frequently found +separating the different lava-flows; and in the upper +amygdaloidal sheets numerous secondary minerals are +found, such as quartz, agate and jasper, stilbite and +chlorite. The total thickness of the whole series, +where complete, is about 6,000 feet, divided as follows:</p> + +<div class="center"> +<table border="0" cellpadding="4" cellspacing="0" summary=""> +<tr> +<td align="left">1. Upper trap; with ash and inter-trappean beds</td> +<td align="right">1,500</td> +<td align="center">feet</td> +</tr> +<tr> +<td align="left">2. Middle trap; sheets of basalt and ash</td> +<td align="right">4,000</td> +<td align="center">"</td> +</tr> +<tr> +<td align="left">3. Lower trap; basalt with inter-trappean beds</td> +<td align="right" style="border-bottom:1px solid black;">500</td> +<td align="center" style="border-bottom:1px solid black;">"</td> +</tr> +<tr> +<td align="left"></td> +<td align="right" style="border-bottom:4px double black;">6,000</td> +<td align="center" style="border-bottom:4px double black;">"</td> +</tr> +</table> +</div> + +<p>Throughout the region here described these great +sheets of volcanic rock are everywhere approximately +horizontal, and constitute a table-land of 3,000 to +4,000 feet in elevation, breaking off in terraced escarpments, +and penetrated by deep river-valleys, of which +the Narbudda is the most important. The foundation +<span class="pagenum"><a name="Page_189" id="Page_189">[Pg 189]</a></span>rock is sometimes metamorphic schist, or gneiss, +at other times sandstone referred by Hislop to +Jurassic age; and in no single instance has a volcanic +crater or focus of eruption been observed. But outside +the central trappean area volcanic foci are numerous, +as in Cutch, the Rajhipla Hills and the Lower Narbudda +valley. The original excessive fluidity of the +Deccan trap is proved by the remarkable horizontality +of the beds over large areas, and the extensive +regions covered by very thin sheets of basalt or dolerite.</p> + +<p>(<i>c.</i>) <i>Geological Age.</i>—As regards the geological age +of this great volcanic series much uncertainty exists, +owing to the absence of marine forms in the inter-trappean +beds. One single species, <i>Cardita variabilis</i>, +has been observed as occurring in these beds, and in +the limestone below the base of the trap at Dudukur. +The <i>facies</i> of the forms in this limestone is Tertiary; +but there is a remarkable absence of characteristic +genera. On the other hand, Mr. Blanford states that +the bedded traps are seen to underlie the Eocene +Tertiary strata with <i>Nummulites</i> in Guzerat and +Cutch,<a name="FNanchor_2_156" id="FNanchor_2_156"></a><a href="#Footnote_2_156" class="fnanchor">[2]</a> which would appear to determine the limit of +their age in one direction. On balancing the evidence, +however, it is tolerably clear that the volcanic eruptions +commenced towards the close of the Cretaceous +period, and continued into the commencement of the +Tertiary, thus bridging over the interval between the +two epochs; and since the greater sheets have been +exposed throughout the whole of the Tertiary and +Quarternary periods, it is not surprising if they have +suffered enormously from denuding agencies, and +that any craters or cones of eruption that may once +have existed have disappeared.</p> + +<div class="footnote"><p><a name="Footnote_1_155" id="Footnote_1_155"></a><a href="#FNanchor_1_155"><span class="label">[1]</span></a> The Deccan Traps have been described by Sykes, <i>Geol. Trans.</i>, 2nd +Series, vol. iv.; also Rev. S. Hislop, "On the Geology of the Neighbourhood +of Nagpur, Central India," <i>Quart. Journ. Geol. Soc.</i>, vol. x. +p. 274; and <i>Ibid.</i>, vol. xvi. p. 154. Also, H. B. Medlicott and W. +T. Blanford, <i>Manual of the Geology of India</i>, vol. i. (1879).</p></div> + +<div class="footnote"><p><a name="Footnote_2_156" id="Footnote_2_156"></a><a href="#FNanchor_2_156"><span class="label">[2]</span></a> Blanford, <i>Geology of Abyssinia</i>, p. 185.</p></div> +<p><span class="pagenum"><a name="Page_190" id="Page_190">[Pg 190]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_V_CHAPTER_II" id="PART_V_CHAPTER_II"></a>CHAPTER II. +<br /><br /> +ABYSSINIAN TABLE-LANDS.</h2> + + +<p>Another region in which the volcanic phenomena +bear a remarkable analogy to those of Central India, +just described, is that of Abyssinia. Nor are these +tracts so widely separated that they may not be +considered as portions of one great volcanic area +extending from Abyssinia, through Southern Arabia, +into Cutch and the Deccan, in the one direction, +while the great volcanic cones of Kenia and Kilimanjaro, +with their surrounding tracts of volcanic matter, +may be the extreme prolongations in the other. Along +this tract volcanic operations are still active in the +Gulf of Aden; and cones quite unchanged in form, +and evidently of very recent date, abound in many +places along the coast both of Arabia and Africa. +The volcanic formations of this tract are, however, +much more recent than those which occupy the +high plateaux of Central and Southern Abyssinia +of which we are about to speak.</p> + +<p>(<i>a.</i>) <i>Physical Features.</i>—Abyssinia forms a compact +region of lofty plateaux intersected by deep +valleys, interposed between the basin of the Nile on +the west, and the low-lying tract bordering the Red +Sea and the Indian Ocean on the east. The plateaux +are deeply intersected by valleys and ravines, giving +<span class="pagenum"><a name="Page_191" id="Page_191">[Pg 191]</a></span>birth to streams which feed the head waters of the +Blue Nile (Bahr el Arak) and the Atbara. Several +fine lakes lie in the lap of the mountains, of which +the Zana, or Dembia, is the largest, and next Ashangi, +visited by the British army on its march to Magdala +in 1868, and which, from its form and the volcanic +nature of the surrounding hills, appears to occupy +the hollow of an extinct crater. The table-land of +Abyssinia reaches its highest elevation along the +eastern and southern margin, where its average +height may be 8,000 to 10,000 feet; but some peaks +rise to a height of 12,000 to 15,000 feet in Shoa and +Ankobar.<a name="FNanchor_1_157" id="FNanchor_1_157"></a><a href="#Footnote_1_157" class="fnanchor">[1]</a></p> + +<p>(<i>b.</i>) <i>Basaltic Lava Sheets.</i>—An enormous area of +this country seems to be composed of volcanic rocks +chiefly in the form of sheets of basaltic lava, which +rise into high plateaux, and break off in steep—sometimes +precipitous—mural escarpments along the +sides of the valleys. These are divisible into the +following series:—</p> + +<p>(1) <i>The Ashangi Volcanic Series.</i>—The earliest +forerunners of the more recent lavas seem to have +been erupted in Jurassic times, in the form of sheets +of contemporaneous basalt or dolerite amongst the +Antola limestones which are of this period. But the +great mass of the volcanic rocks are much more +recent, and may be confidently referred to the late +Cretaceous or early Tertiary epochs. Their resemblance +to the great trappean series of Western India, +even in minute particulars, is referred to by Mr. +Blanford, who suggests the view that they belong +to one and the same great series of lava-flows extruded +over the surface of this part of the globe. +<span class="pagenum"><a name="Page_192" id="Page_192">[Pg 192]</a></span>This view is inherently probable. They consist of +basalts and dolerites, generally amygdaloidal, with +nodules of agate and zeolite, and are frequently coated +with green-earth (chlorite). Beds of volcanic ash +or breccia also frequently occur, and often contain +augite crystals. At Senafé, hills of trachyte passing +into claystone and basalt were observed by Mr. +Blanford, but it is not clear what are their relations +to the plateau-basaltic sheets.<a name="FNanchor_2_158" id="FNanchor_2_158"></a><a href="#Footnote_2_158" class="fnanchor">[2]</a></p> + +<p>(2) <i>Magdala Volcanic Series.</i>—This is a more recent +group of volcanic lavas, chiefly distinguished from +the lower, or Ashangi, group, by the occurrence of +thick beds of trachyte, usually more or less crystalline, +and containing beautiful crystals of sanidine. +The beds of trachyte break off in precipitous scarps, +and being of great thickness and perfectly horizontal, +are unusually conspicuous. Mr. Blanford says, with +regard to this group, that there is a remarkable resemblance +in its physical aspect to the scenery of the +Deccan and the higher valleys of the Western Ghats +of India, but the peculiarities of the landscape are +exaggerated in Abyssinia. Many of the trachytic +beds are brecciated and highly columnar; sedimentary +beds are also interstratified with those of volcanic +origin. The Magdala group is unconformable to +that of Ashangi in some places. A still more recent +group of volcanic rocks appears to occur in the +neighbourhood of Senafé, consisting of amorphous +masses of trachyte, often so fine-grained and compact +as to pass into claystone and to resemble sandstone. +At Akub Teriki the rocks appear to be in the immediate +vicinity of an ancient vent of eruption.</p> + +<p>From what has been said, it will be apparent that +<span class="pagenum"><a name="Page_193" id="Page_193">[Pg 193]</a></span>Abyssinia offers volcanic phenomena of great interest +for the observer. There is considerable variety in +the rock masses, in their mode of distribution, and +in the scenery which they produce. The extensive +horizontal sheets of lava are suggestive of fissure-eruption +rather than of eruption through volcanic +craters; and although these may have once been in +existence, denudation has left no vestiges of them at +the present day. In all these respects the resemblance +of the volcanic phenomena to those of Peninsular +India is remarkably striking; it suggests the +view that they are contemporaneous as regards the +time of their eruption, and similar as regards their +mode of formation.</p> + +<div class="footnote"><p><a name="Footnote_1_157" id="Footnote_1_157"></a><a href="#FNanchor_1_157"><span class="label">[1]</span></a> W. T. Blanford, <i>Geology of Abyssinia</i>, pp. 151-2.</p></div> + +<div class="footnote"><p><a name="Footnote_2_158" id="Footnote_2_158"></a><a href="#FNanchor_2_158"><span class="label">[2]</span></a> Blanford, <i>loc. cit.</i>, p. 182.</p></div> +<p><span class="pagenum"><a name="Page_194" id="Page_194">[Pg 194]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_V_CHAPTER_III" id="PART_V_CHAPTER_III"></a>CHAPTER III. +<br /><br /> +CAPE COLONY.</h2> + + +<p><i>Basalt of the Plateau.</i>—The extensive sheets of +plateau-basalt forming portions of the Neuweld range +and the elevated table-land of Cape Colony, may be +regarded as forerunners of those just described, and +possibly contemporaneous with the Ashangi volcanic +series of Abyssinia. The great basaltic sheets of +the Cape Colony are found capping the highest +elevations of the Camderboo and Stormberg ranges, +as well as overspreading immense areas of less +elevated land, to an extent, according to Professor +A. H. Green, of at least 120,000 square miles.<a name="FNanchor_1_159" id="FNanchor_1_159"></a><a href="#Footnote_1_159" class="fnanchor">[1]</a> +Amongst these sheets, innumerable dykes, and masses +of solid lava which filled the old vents of eruption, +are to be observed. The floor upon which the lava-floods +have been poured out generally consists of the +"Cave Sandstone," the uppermost of a series of +deposits which had previously been laid down over +the bed of an extensive lake which occupied this +part of Africa during the Mesozoic period. After +the deposition of this sandstone, the volcanic forces +appear to have burst through the crust, and from +<span class="pagenum"><a name="Page_195" id="Page_195">[Pg 195]</a></span>vents and fissures great floods of augitic lava, with +beds of tuff, invaded the region occupied by the +waters of the lake. The lava-sheets have since +undergone extensive denudation, and are intersected +by valleys and depressions eroded down through +them into the sandstone floor beneath; and though +the precise geological period at which they were +extruded must remain in doubt, it appears probable +that they may be referred to that of the Trias.<a name="FNanchor_2_160" id="FNanchor_2_160"></a><a href="#Footnote_2_160" class="fnanchor">[2]</a></p> + +<div class="footnote"><p><a name="Footnote_1_159" id="Footnote_1_159"></a><a href="#FNanchor_1_159"><span class="label">[1]</span></a> Green. "On the Geology of the Cape Colony," <i>Quart. Jour. Geol. +Soc.</i>, vol. xliv. (1888).</p></div> + +<div class="footnote"><p><a name="Footnote_2_160" id="Footnote_2_160"></a><a href="#FNanchor_2_160"><span class="label">[2]</span></a> The district lying along the south coast of Africa is described +by Andrew G. Bain, in the <i>Trans. Geol. Soc.</i>, vol. vii. (1845); but +there is little information regarding the volcanic region here referred to.</p></div> +<p><span class="pagenum"><a name="Page_196" id="Page_196">[Pg 196]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_V_CHAPTER_IV" id="PART_V_CHAPTER_IV"></a>CHAPTER IV. +<br /><br /> +VOLCANIC ROCKS OF PAST GEOLOGICAL PERIODS +OF THE BRITISH ISLES.</h2> + + +<p>It is beyond the scope of this work to describe the +volcanic rocks of pre-Tertiary times over various parts +of the globe. The subject is far too large to be treated +otherwise than in a distinct and separate essay. I +will therefore content myself with a brief enumeration +of the formations of the British Isles in which contemporaneous +volcanic action has been recognised.<a name="FNanchor_1_161" id="FNanchor_1_161"></a><a href="#Footnote_1_161" class="fnanchor">[1]</a></p> + +<p>There is little evidence of volcanic action throughout +the long lapse of time extending backwards from +the Cretaceous to the Triassic epochs, that is to say, +throughout the Mesozoic or Secondary period, and it +is not till we reach the Palæozoic strata that evidence +of volcanic action unmistakably presents itself.</p> + +<p><i>Permian Period.</i>—In Ayrshire, and in the western +parts of Devonshire, beds of felspathic porphyry, felstone +and ash are interstratified with strata believed +to be of Permian age. In Devonshire these have only +recently been recognised by Dr. Irving and the author +as of Permian age, the strata consisting of beds of +breccia, lying at the base of the New Red Sandstone. +Those of Ayrshire have long been recognised as of +<span class="pagenum"><a name="Page_197" id="Page_197">[Pg 197]</a></span>the same period; as they rest unconformably on the +coal measures, and consist of porphyrites, melaphyres, +and tuffs of volcanic origin.</p> + +<p><i>Carboniferous Period.</i>—Volcanic rocks occur +amongst the coal-measures of England and Scotland, +while they are also found interbedded with the +Carboniferous Limestone series in Derbyshire, Scotland, +and Co. Limerick in Ireland. The rocks consist +chiefly of basalt, dolerite, melaphyre and felstone.</p> + +<p><i>Devonian Period.</i>—Volcanic rocks of Devonian +age occur in the South of Scotland, consisting of +felstone-porphyries and melaphyres; also at Boyle, +in Roscommon, and amongst the Glengariff beds +near Killarney in Ireland.</p> + +<p><i>Upper Silurian Period.</i>—Volcanic rocks of this +stage are only known in Ireland, on the borders of +Cos. Mayo and Galway, west of Lough Mask, and at +the extreme headland of the Dingle Promontory in +Co. Kerry. They consist of porphyrites, felstones +and tuffs, or breccias, contemporaneously erupted +during the Wenlock and Ludlow stages. Around +the flanks of Muilrea, beds of purple quartz-felstone +with tuff are interstratified with the Upper Silurian +grits and slates.</p> + +<p><i>Lower Silurian Period.</i>—Volcanic action was developed +on a grand scale during the Arenig and Caradoc-Bala +stages, both in Wales and the Lake district, +and in the Llandeilo stage in the South of Scotland. +The felspathic lavas, with their associated beds of +tuff and breccia, rise into some of the grandest mountain +crests of North Wales, such as those of Cader +Idris, Aran Mowddwy, Arenig and Moel Wyn. A +similar series is also represented in Ireland, ranging +from Wicklow to Waterford, forming a double group +<span class="pagenum"><a name="Page_198" id="Page_198">[Pg 198]</a></span>of felstones, porphyries, breccias, and ash-beds, with +dykes of basalt and dolerite. The same series again +appears amidst the Lower Silurian beds of Co. Louth, +near Drogheda.</p> + +<p><i>Metamorphic Series presumably of Lower Silurian +Age.</i>—If, as seems highly probable, the great metamorphic +series of Donegal and Derry are the representatives +in time of the Lower Silurian series, +some of the great sheets of felspathic and hornblendic +trap which they contain are referable to this +epoch. These rocks have undergone a change in +structure along with the sedimentary strata of which +they were originally formed, so that the sheets of (presumably) +augitic lava have been converted into hornblende-rock +and schist. Similar masses occur in North +Mayo, south of Belderg Harbour.</p> + +<p><i>Cambrian Period.</i>—In the Pass of Llanberis, along +the banks of Llyn Padarn, masses of quartz-porphyry, +felsite and agglomerate, or breccia, indicate volcanic +action during this stage. These rocks underlie beds +of conglomerate, slate and grit of the Lower Cambrian +epoch, and, as Mr. Blake has shown, are clearly +of volcanic origin, and pass upwards into the sedimentary +strata of the period. A similar group, first +recognised by Professor Sedgwick, stretches southwards +from Bangor along the southern shore of the +Menai Straits. Again, we find the volcanic eruptions +of this epoch at St. David's, consisting of diabasic and +felsitic lava, with beds of ash; and in the centre of +England, amongst the grits and slates of Charnwood +Forest presumably of Cambrian age, various felstones, +porphyries, and volcanic breccias are found.</p> + +<p>Thus it will be seen that every epoch, from the +earliest stage of the Cambrian to the Permian, in the +<span class="pagenum"><a name="Page_199" id="Page_199">[Pg 199]</a></span>British Isles, gives evidence of the existence of volcanic +action; from which we may infer that the +originating cause, whatever it may be, has been in +operation throughout all past geological time represented +by living forms. The question of the condition +of our globe in Archæan times, and earlier, is +one which only can be discussed on theoretic ground, +and is beyond the scope of this work.</p> + +<div class="footnote"><p><a name="Footnote_1_161" id="Footnote_1_161"></a><a href="#FNanchor_1_161"><span class="label">[1]</span></a> The reader is referred to Sir A. Geikie's Presidential Address to the +Geological Society (1891) for the latest view of this subject.</p></div> + +<p><span class="pagenum"><a name="Page_200" id="Page_200">[Pg 200]</a></span></p> +<hr class="major" /> + +<div class="figcenter"> +<a name="MAP_2"></a> +<a href="images/map2full.jpg"> + <span class="center">VOLCANIC BAND OF THE MOLUCCAS.</span><br /> + <img src="images/map2.jpg" alt="Map of Moluccas" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +Map showing the volcanic belt to which Krakatoa belongs. The shaded portion is volcanic. +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_201" id="Page_201">[Pg 201]</a></span></p> +<hr class="major" /> + + +<h1><a name="PART_VI" id="PART_VI"></a>PART VI. +<br /><br /> +SPECIAL VOLCANIC AND SEISMIC +PHENOMENA.</h1> + + + +<hr class="major" /> +<h2><a name="PART_VI_CHAPTER_I" id="PART_VI_CHAPTER_I"></a>CHAPTER I. +<br /><br /> +THE ERUPTION OF KRAKATOA IN 1883.</h2> + + +<p>I propose to introduce here some account of one +of the most terrible outbursts of volcanic action +that have taken place in modern times; namely, +the eruption of the volcano of Krakatoa (a corruption +of Rakata) in the strait of Sunda, between +the islands of Sumatra and Java, in the year 1883. +The Malay Archipelago, of which this island once +formed a member, is a region where volcanic action +is constant, and where the outbursts are exceptionally +violent. With the great island of Borneo +as a solid, non-volcanic central core, a line of volcanic +islands extends from Chedooba off the coast +of Pegu through Sumatra, Java, Sumbawa, Flores, +and, reaching the Moluccas, stretches northwards +through the Philippines into Japan and Kamtschatka. +This is probably the most active volcanic belt in the +world, and the recent terrible earthquake and eruption +in Japan (November, 1891) gives proof that the +volcanic forces are as powerful and destructive as ever.<a name="FNanchor_1_162" id="FNanchor_1_162"></a><a href="#Footnote_1_162" class="fnanchor">[1]</a></p> + +<p><span class="pagenum"><a name="Page_202" id="Page_202">[Pg 202]</a></span></p><p>(<i>a.</i>) <i>Dormant Condition down to 1680.</i>—Down to +the year 1680, this island, although from its form and +structure evidently volcanic, appears to have been +in a dormant state; its sides were covered with +luxuriant forests, and numerous habitations dotted +its shore. But in May of that year an eruption +occurred, owing to which the aspect of Krakatoa +as described by Vogel was entirely changed; the +surface of the island when this writer passed on +his voyage to Sumatra appeared burnt up and arid, +while blocks of incandescent rock were being hurled +into the air from four distinct points. After this first +recorded eruption the island relapsed into a state of +repose, and except for a stream of molten lava which +issued from the northern extremity, there was no +evidence of its dangerous condition. The luxuriant +vegetation of the tropics speedily re-established +itself, and the volcano was generally regarded as +"extinct."<a name="FNanchor_2_163" id="FNanchor_2_163"></a><a href="#Footnote_2_163" class="fnanchor">[2]</a> History repeats itself; and the history +of Vesuvius was repeated in the case of Krakatoa.</p> + +<p><span class="pagenum"><a name="Page_203" id="Page_203">[Pg 203]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_35"> + <img src="images/figure35.jpg" alt="Map of Krakatoa" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 35.</span>—Map +Of The Krakatoa Group Of Islands Before +The Eruption Of August 1883 (From Admiralty Chart) +</td></tr> +</table> +</div> + +<p>(<i>b.</i>) <i>Eruption of May, 1883.</i><a name="FNanchor_3_164" id="FNanchor_3_164"></a><a href="#Footnote_3_164" class="fnanchor">[3]</a>—On the morning of +May 20, 1883, the inhabitants of Batavia, of Buitenzorg, +and neighbouring localities, were surprised by a +confused noise, mingled with detonations resembling +the firing of artillery. The phenomena commenced +between ten and eleven o'clock in the morning, and +soon acquired such intensity as to cause general +alarm. The detonations were accompanied by +tremblings of the ground, of buildings and various +objects contained in dwellings; but it was generally +admitted that these did not proceed from earthquake +shocks, but from atmospheric vibrations. No deviation +of the magnetic needle was observed at the Meteorological +Institute of Batavia; but a vertical oscillation +was apparent, and persons who listened with the ear +placed on the ground, even during the most violent +detonations, could hear no subterranean noise whatever. +It became clear that the sounds came from +some volcano burst into activity; but it is strange that +for two whole days it remained uncertain what was +the particular volcano to which the phenomena were +to be referred. The detonations appeared, indeed, to +come from the direction of Krakatoa; but from +<span class="pagenum"><a name="Page_204" id="Page_204">[Pg 204]</a></span>Serang, Anjer, and Merak, localities situated much +nearer Krakatoa than Batavia, the telegraph announced +that neither detonations nor atmospheric +vibrations had been perceived. The distance between +Batavia and Krakatoa is ninety-three English miles. +The doubts thus experienced were, however, soon put +to rest by the arrival of an American vessel under the +command of A. R. Thomas, and of other ships which +hailed from the straits of Sunda. From their accounts +it was ascertained that in the direction of Krakatoa +the heavens were clouded with ashes, and that a grand +column of smoke, illumined from time to time by +flashes of flame, arose from above the island. Thus +after a repose of more than two hundred years, "the +peaceable isle of Krakatoa, inhabited, and covered by +thick forests, was suddenly awakened from its condition +of fancied security."</p> + +<div class="figcenter"> +<a name="FIGURE_36"> + <img src="images/figure36.jpg" alt="Section through Krakatoa" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 36.</span>—Section from Verlaten Island through Krakatoa, to show +the outline before and after the eruption of August, 1888. The continuous +line shows the former; the dotted line and shading, the latter; +from which it will be observed that the original island has to a large +extent disappeared. The line of section is shown in <a href="#FIGURE_35">Fig. 35</a>. +</td></tr> +</table> +</div> + +<p>(<i>c.</i>) <i>Form and Appearance of the Island before the +Eruption of 1883.</i>—From surveys made in 1849 and +1881, it would appear that the island of Krakatoa +consisted of three mountains or groups of mountains +(Figs. <a href="#FIGURE_35">35</a>, <a href="#FIGURE_36">36</a>); the southern formed by the cone of Rakata +(properly so called), rising with a scarped face +above the sea to a height of over 800 mètres (2,622 +feet). Adjoining this cone, and rising from the centre of +<span class="pagenum"><a name="Page_205" id="Page_205">[Pg 205]</a></span>the island, came the group of Danan, composed of +many summits, probably forming part of the <i>enceinte +annulaire</i> of a crater. And near the northern +extremity of the isle, a third group of mammelated +heights could be recognised under the general name +of Perboewatan, from which issued several obsidian +lava-flows, with a steep slope; these dated back perhaps +to the period of the first known eruption of 1680. +This large and mountainous island as it existed at the +beginning of May, 1883, has been entirely destroyed +by the terrible eruptions of that year, with the exception +of the peripheric rim (composed of the most +ancient of the volcanic rocks, andesite), of which Verlaten +Island and Rakata formed a part, and one very +small islet, which is noted on the maps as "rots" +(rock), and on the new map of the Straits of Sunda +of the Dutch Navy as that of "Bootsmansrots."<a name="FNanchor_4_165" id="FNanchor_4_165"></a><a href="#Footnote_4_165" class="fnanchor">[4]</a></p> + +<p>As shown by the map in the Report of the Royal +Society, the group of islands which existed previous +to 1883 were but the unsubmerged portions of one +vast volcanic crater, built up of a remarkable variety +of lava allied to the andesite of the Java volcanoes, +but having a larger percentage of silica, and hence +falling under the head of "enstatite-dacite."<a name="FNanchor_5_166" id="FNanchor_5_166"></a><a href="#Footnote_5_166" class="fnanchor">[5]</a> That +these volcanic rocks are of very recent origin is shown +by the fact, ascertained by Verbeek, that beneath them +occur deposits of Post-Tertiary age, and that these in +turn rest on the Tertiary strata which are widely distributed +through Sumatra, Java, and the adjoining +islands. According to the reasoning of Professor +Judd, the Krakatoa group at an early period of its +history presented the form of a magnificent crater-cone, +several miles in circumference at the base, which +<span class="pagenum"><a name="Page_206" id="Page_206">[Pg 206]</a></span>subsequent eruptions shattered into fragments or blew +into the air in the form of dust, ashes, and blocks +of lava, while the central part collapsed and fell in, +leaving a vast circular ring like the ancient crater of +Somma (see <a href="#FIGURE_6">Fig. 6, p. 43</a>), and he supposes the +former eruptions to have been on a scale exceeding +in magnificence those which have caused such +world-wide interest within the last few years.</p> + +<p>(<i>d.</i>) <i>Eruption of 26th to 28th of August.</i>—It was, +as we have seen, in the month of May that, in the +language of Chev. Verbeek, "the volcano of Krakatoa +chose to announce in a high voice to the inhabitants +of the Archipelago that, although almost nothing +amongst the many colossal volcanic mountains of the +Indies, it yielded to none of them in regard to its power." +These eruptions were, however, only premonitory of +the tremendous and terrible explosion which was to +commence on Sunday, the 26th of August, and which +continued for several days subsequently. A little +after noon of that day, a rumbling noise accompanied +by short and feeble explosions was heard at Buitenzorg, +coming from the direction of Krakatoa; and +similar sounds were heard at Anjer and Batavia a +little later. Soon these detonations augmented in +intensity, especially about five o'clock in the evening; +and news was afterwards received that the sounds +had been heard in the isle of Java. These sounds +increased still more during the night, so that few +persons living on the west side of the isle of Java +were able to sleep. At seven in the morning there +came a crash so formidable, that those who had hoped +for a little sleep at Buitenzorg leaped from their beds. +Meanwhile the sky, which had up to this time been +clear, became overcast, so that by ten o'clock it +<span class="pagenum"><a name="Page_207" id="Page_207">[Pg 207]</a></span>became necessary to have recourse to lamps, and the +air became charged with vapour. Occasional shocks +of earthquake were now felt. Darkness became +general all over the straits and the bordering coasts. +Showers of ashes began to fall. The repeated shocks +of earthquake, and the rapid discharges of subterranean +artillery, all combined to show that an eruption +of even greater violence than that of May was in +progress at the isle of Krakatoa.</p> + +<p>But the most interested witnesses to this terrible +outburst were those on board the ships plying through +the straits. Amongst these was the <i>Charles Bal</i>, a +British vessel under the command of Captain Watson. +This ship was ten miles south of the volcano on Sunday +afternoon, and therefore well in sight of the island +at the time when the volcano had entered upon its +paroxysmal state of action. Captain Watson describes +the island as being covered by a dense black cloud, +while sounds like the discharges of artillery occurred +at intervals of a second of time; and a crackling noise +(probably arising from the impact of fragments of +rock ascending and descending in the atmosphere) +was heard by those on board. These appearances +became so threatening towards five o'clock in the +evening, that the commander feared to continue his +voyage and began to shorten sail. From five to six +o'clock a rain of pumice in large pieces, quite warm, +fell upon the ship, which was one of those that escaped +destruction during this terrible night.<a name="FNanchor_6_167" id="FNanchor_6_167"></a><a href="#Footnote_6_167" class="fnanchor">[6]</a></p> + +<p>(<i>e.</i>) <i>Electrical Phenomena.</i>—During this eruption, +electrical phenomena of great splendour were observed. +<span class="pagenum"><a name="Page_208" id="Page_208">[Pg 208]</a></span>Captain Wooldbridge, viewing the eruption +in the afternoon of the 26th from a distance of forty +miles, speaks of a great vapour-cloud looking like an +immense wall being momentarily lighted up "by +bursts of forked lightning like large serpents rushing +through the air. After sunset this dark wall resembled +a blood-red curtain, with edges of all shades of +yellow, the whole of a murky tinge, through which +gleamed fierce flashes of lightning." As Professor +Judd observes, the abundant generation of atmospheric +electricity is a familiar phenomenon in all +volcanic eruptions on a grand scale. The steam-jets +rushing through the orifices of the earth's crust +constitute an enormous hydro-electrical engine, and +the friction of the ejected materials striking against +one another in their ascent and descent also does +much in the way of generating electricity.<a name="FNanchor_7_168" id="FNanchor_7_168"></a><a href="#Footnote_7_168" class="fnanchor">[7]</a> It has +been estimated by several observers that the column of +watery vapour ascended to a height of from twelve to +seventeen and even twenty-three miles; and on reaching +the upper strata of the atmosphere, it spread itself +out in a vast canopy resembling "the pine-tree" form +of Vesuvian eruptions; and throughout the long night +of the 27th this canopy continued to extend laterally, +and the particles of dust which it enclosed began to +descend slowly through the air.</p> + +<p>(<i>f.</i>) <i>Formation of Waves.</i>—This tremendous outburst +of volcanic forces, which to a greater or less +extent influenced the entire surface of the globe, gave +rise to waves which traversed both air and ocean; and +in consequence of the large number of observatories +scattered all over the globe, and the excellence and +delicacy of the instruments of observation, we are +<span class="pagenum"><a name="Page_209" id="Page_209">[Pg 209]</a></span>put in possession of the remarkable results which +have been obtained from the collection of the observations +in the hands of competent specialists. +The results are related <i>in extenso</i> in the Report +of the Royal Society, illustrated by maps and diagrams, +and are worthy of careful study by those +interested in terrestrial phenomena. A brief summary +is all that can be given here, but it will probably +suffice to bring home to the reader the magnitude +and grandeur of the eruption.</p> + +<p>The vibrations or waves generated in August, 1883, +at Krakatoa may be arranged under three heads: +(1) Atmospheric Waves; (2) Sound Waves; and (3) +Oceanic Waves; which I will touch upon in the order +here stated.</p> + +<p>(1) <i>Atmospheric Waves.</i>—These phenomena have +been ably handled by General Strachey,<a name="FNanchor_8_169" id="FNanchor_8_169"></a><a href="#Footnote_8_169" class="fnanchor">[8]</a> from a +large number of observations extending all over the +globe. From these it has been clearly established that +an atmospheric wave, originating at Krakatoa as a +centre, expanded outwards in a circular form and +travelled onwards till it became a great circle at a +distance of 180 degrees from its point of origin, after +which it still advanced, but now gradually contracting +to a node at the antipodes of Krakatoa; that is to +say, at a point over the surface of North America, +situated in lat. 6° N. and long. 72° W. (or thereabout). +Having attained this position, the wave was reflected +or reproduced, expanding outwards for 180 degrees +and travelling backwards again to Krakatoa, from +which it again started, and returning to its original +form again overspread the globe. This wonderful +repetition, due to the spherical form of the earth, was +<span class="pagenum"><a name="Page_210" id="Page_210">[Pg 210]</a></span>observed no fewer than seven times, though with such +diminished force as ultimately to be outside the range +of observation by the most sensitive instruments. It +is one of the triumphs of modern scientific appliances +that the course of such a wave, generated in a fluid +surrounding a globe, which might be demonstrated on +mathematical principles, has been actually determined +by experiments carried on over so great an area.</p> + +<p>(2) <i>Sound Waves.</i>—If the sound-waves produced +at the time of maximum eruption were not quite as +far-reaching as those of the air, they were certainly +sufficiently surprising to be almost incredible, were it +not that they rest, both as regards time and character, +upon incontestible authority. The sound of the +eruption, resembling that of the discharge of artillery, +was heard not only over nearly all parts of Sumatra, +Java, and the coast of Borneo opposite the Straits of +Sunda, but at places over two thousand miles distant +from the scene of the explosions. Detailed accounts, +collected with great care, are given in the Report of +the Royal Society, from which the following are +selected as examples:—</p> + +<blockquote><p>1. At the port of Acheen, at the northern extremity of Sumatra, +distant 1,073 miles, it was supposed that the port was being +attacked, and the troops were put under arms.</p> + +<p>2. At Singapore, distant 522 miles, two steamers were dispatched +to look out for the vessel which was supposed to be +firing guns as signals of distress.</p> + +<p>3. At Bankok, in Siam, distant 1,413 miles, the report was +heard on the 27th; as also at Labuan, in Borneo, distant 1,037 +miles.</p> + +<p>4. At places in the Philippine Islands, distant about 1,450 +miles, detonations were heard on the 27th, at the time of the +eruption.</p></blockquote> + +<p>The above places lie northwards of Krakatoa. In +<span class="pagenum"><a name="Page_211" id="Page_211">[Pg 211]</a></span>the opposite direction, we have the following examples:—</p> + +<blockquote><p>5. At Perth, in Western Australia, distant 1,092 miles, sounds +as of guns firing at sea were heard; and at the Victorian Plains, +distant about 1,700 miles, similar sounds were heard.</p> + +<p>6. In South Australia, at Alice's Springs, Undoolga, and +other places at distances of over 2,000 miles, the sounds of the +eruption were also heard.</p> + +<p>7. In a westerly direction at Dutch Bay, Ceylon, distant +2,058 miles, the sounds were heard between 7 a.m. and 10 a.m. +on the morning of the 27th of August.</p> + +<p>8. Lastly, at the Chagos Islands, distant 2,267 miles, the detonations +were audible between 10 and 11 a.m. of the same day.</p></blockquote> + +<p>Some of the above distances are so great that we +may fail to realise them; but they will be more easily +appreciated, perhaps, if we change the localities to our +own side of the globe, and take two or three cases +with similar distances. Then, if the eruption had taken +place amongst the volcanoes of the Canaries, the detonations +would have been heard at Gibraltar, at Lisbon, +at Portsmouth, Southampton, Cork, and probably at +Dublin and Liverpool; or, again, supposing the eruption +had taken place on the coast of Iceland, the +report would have been heard all over the western +and northern coasts of the British Isles, as well as at +Amsterdam and the Hague. The enormous distance +to which the sound travelled in the case of Krakatoa +was greatly due to the fact that the explosions took +place at the surface of the sea, and the sound was +carried along that surface uninterruptedly to the +localities recorded; a range of mountains intervening +would have cut off the sound-wave at a comparatively +short distance from its source.</p> + +<p>(3) <i>Oceanic Waves.</i>—As may be supposed, the +<span class="pagenum"><a name="Page_212" id="Page_212">[Pg 212]</a></span>eruption gave rise to great agitation of the ocean +waters with various degrees of vertical oscillation; +but according to the conclusions of Captain Wharton, +founded on numerous data, the greatest wave seems +to have originated at Krakatoa about 10 a.m. on the +27th of August, rising on the coasts of the Straits of +Sunda to a height of fifty feet above the ordinary sea-level. +This wave appears to have been observed over +at least half the globe. It travelled westwards to the +coast of Hindostan and Southern Arabia, ultimately +reaching the coasts of France and England. Eastwards +it struck the coast of Australia, New Zealand, +the Sandwich Islands, Alaska, and the western coast +of North America; so that it was only the continent +of North and South America which formed a barrier +(and that not absolute) to the circulation of this +oceanic wave all over the globe. The destruction to +life and property caused by this wave along the coasts +of Sunda was very great. Combined with the earthquake +shocks (which, however, were not very severe), +the tremendous storm of wind, the fall of ashes +and cinders, and the changes in the sea-bed, it produced +in the Straits of Sunda for some time after the +eruption a disastrous transformation. Lighthouses +had been swept away; all the old familiar landmarks +on the shore were obscured by a vast deposit of +volcanic dust; the sea itself was encumbered with +enormous quantities of floating pumice, in many +places of such thickness that no vessel could force its +way through them; and for months after the eruption +one of the principal channels was greatly obstructed +by two islands which had arisen in its midst. The +Sebesi channel was completely blocked by banks +composed of volcanic materials, and two portions of +<span class="pagenum"><a name="Page_213" id="Page_213">[Pg 213]</a></span>these banks rose above the sea as islands, which +received the name of "Steers Island" and "Calmeyer +Island"; but these, by the action of the waves, have +since been completely swept away, and the materials +strewn over the bed of the sea.<a name="FNanchor_9_170" id="FNanchor_9_170"></a><a href="#Footnote_9_170" class="fnanchor">[9]</a></p> + +<p>(<i>g.</i>) <i>Atmospheric Effects.</i>—But the face of nature, +even in her most terrific and repulsive aspect, is seldom +altogether unrelieved by some traces of beauty. +In contrast to the fearful and disastrous phenomena +just described, is to be placed the splendour of the +heavens, witnessed all over the central regions of +the globe throughout a period of several months after +the eruption of 1883, which has been ably treated +by the Hon. Rollo Russell and Mr. C. D. Archibald, +in the Royal Society's Report.</p> + +<p>When the particles of lava and ashes mingled with +vapour were projected into the air with a velocity +greater than that of a ball discharged from the largest +Armstrong gun, these materials were carried by the +prevalent trade-winds in a westerly direction, and +some of them fell on the deck of ships sailing in +the Indian Ocean as far as long. 80° E., as in the case +of the <i>British Empire</i>—on which the particles fell on +the 29th of August, at a distance of 1,600 miles from +Krakatoa. But far beyond this limit, the finer particles +of dust (or rather minute crystals of felspar and other +minerals), mingled with vapour of water, were carried +by the higher currents of the air as far as the Seychelles +and Africa,—not only the East coast, but also +the West, as Cape Coast Castle on the Gold Coast; to +Paramaribo, Trinidad, Panama, the Sandwich Isles, +<span class="pagenum"><a name="Page_214" id="Page_214">[Pg 214]</a></span>Ceylon and British India, at all of which places during +the month of September the sun assumed tints of blue +or green, as did also the moon just before and after the +appearance of the stars;<a name="FNanchor_10_171" id="FNanchor_10_171"></a><a href="#Footnote_10_171" class="fnanchor">[10]</a> and from the latter end of +September and for several months, the sky was remarkable +for its magnificent coloration; passing from +crimson through purple to yellow, and melting away +in azure tints which were visible in Europe and the +British Isles; while a large corona was observed round +both the sun and moon. These beautiful sky effects +were objects of general observation throughout the +latter part of the year 1883 and commencement of the +following year.</p> + +<p>The explanation of these phenomena may be briefly +stated. The fine particles, consisting for the most +part of translucent crystals, or fragments of crystals, +formed a canopy high up in the atmosphere, being +gradually spread over both sides of the equator till it +formed a broad belt, through which the rays of the +sun and moon were refracted. Towards dawn and +sunset they were refracted and reflected from the +facets of the crystal, and thus underwent decomposition +into the prismatic colours; as do the rays of the +sun when refracted and reflected from the particles of +moisture in a rain-cloud. The subject is one which +cannot be fully dealt with here, and is rather outside +the scope of this work.</p> + +<p>(<i>h.</i>) <i>Origin of the Eruption.</i>—The ultimate cause of +volcanic eruptions is treated in a subsequent chapter, +nor is that of Krakatoa essentially different from +others. It was remarkable, however, both for the +magnitude of the forces evoked and the stupendous +<span class="pagenum"><a name="Page_215" id="Page_215">[Pg 215]</a></span>scale of the resulting phenomena. It is evident that +water played an important part in these phenomena, +though not as the prime mover;—any more than water +in the boiler of a locomotive is the prime mover in +the generation of the steam. Without the fuel in the +furnace the steam would not be produced; and the +amount of steam generated will be proportional to +the quantity and heat of the fuel in the furnace and +the quantity of water in the boiler. In the case of +Krakatoa, both these elements were enormous and +inexhaustible. The volcanic chimney (or system of +chimneys), being situated on an island, was readily +accessible to the waters of the ocean when fissures +gave them access to the interior molten matter. That +such fissures were opened we may well believe. The +earthquakes which occurred at the beginning of May, +and later on, on the 27th of that month, may indicate +movements of the crust by which water gained access. +It appears that in May the only crater in a state of +activity was that of Perboewatan; in June another +crater came into action, connected with Danan in the +centre of the island, and in August a third burst forth. +Thus there was progressive activity up to the commencement +of the grand eruption of the 26th of that +month.<a name="FNanchor_11_172" id="FNanchor_11_172"></a><a href="#Footnote_11_172" class="fnanchor">[11]</a> During this last paroxysmal stage, the centre +of the island gave way and sunk down, when the waters +of the ocean gained free access, and meeting with the +columns of molten matter rising from below originated +the prodigious masses of steam which rose into the +air.</p> + +<p>(<i>i.</i>) <i>Cause of the Detonations.</i>—The detonations +which accompanied the last great eruption are +repeatedly referred to in all the accounts. These +<span class="pagenum"><a name="Page_216" id="Page_216">[Pg 216]</a></span>may have been due, not only to the sudden explosions +of steam directly produced by the ocean water coming +in contact with the molten lava, but by dissociation of +the vapour of water at the critical point of temperature +into its elements of oxygen and hydrogen; the +reunion of these elements at the required temperature +would also result in explosions.</p> + +<p>The phenomena attending this great volcanic eruption, +so carefully tabulated and critically examined, +will henceforth be referred to as constituting an epoch +in the history of volcanic action over the globe, and be +of immense value for reference and comparison.</p> + +<div class="footnote"><p><a name="Footnote_1_162" id="Footnote_1_162"></a><a href="#FNanchor_1_162"><span class="label">[1]</span></a> The eruption of Krakatoa has been the subject of an elaborate +Report published by the Royal Society, and is also described in a +work by Chevalier R. D. M. Verbeek, Ingenieur en Chef des Mines, +and published by order of the Governor-General of the Netherland +Indies (1886). See also an Article by Sir R. S. Ball in the <i>Contemporary +Review</i> for November, 1888.</p></div> + +<div class="footnote"><p><a name="Footnote_2_163" id="Footnote_2_163"></a><a href="#FNanchor_2_163"><span class="label">[2]</span></a> Verbeek, <i>loc. cit.</i>, p. 4.</p></div> + +<div class="footnote"><p><a name="Footnote_3_164" id="Footnote_3_164"></a><a href="#FNanchor_3_164"><span class="label">[3]</span></a> The account of this eruption is a free translation from Verbeek.</p></div> + +<div class="footnote"><p><a name="Footnote_4_165" id="Footnote_4_165"></a><a href="#FNanchor_4_165"><span class="label">[4]</span></a> Verbeek, <i>loc. cit.</i>, p. 160.</p></div> + +<div class="footnote"><p><a name="Footnote_5_166" id="Footnote_5_166"></a><a href="#FNanchor_5_166"><span class="label">[5]</span></a> Judd, <i>Rep. R. S.</i></p></div> + +<div class="footnote"><p><a name="Footnote_6_167" id="Footnote_6_167"></a><a href="#FNanchor_6_167"><span class="label">[6]</span></a> A fuller account by Prof. Judd will be found in the <i>Report of the +Royal Society</i>, p. 14. Several vessels at anchor were driven ashore on +the straits owing to the strong wind which arose.</p></div> + +<div class="footnote"><p><a name="Footnote_7_168" id="Footnote_7_168"></a><a href="#FNanchor_7_168"><span class="label">[7]</span></a> Judd, <i>Report</i>, p. 21.</p></div> + +<div class="footnote"><p><a name="Footnote_8_169" id="Footnote_8_169"></a><a href="#FNanchor_8_169"><span class="label">[8]</span></a> <i>Report</i>, Part ii.</p></div> + +<div class="footnote"><p><a name="Footnote_9_170" id="Footnote_9_170"></a><a href="#FNanchor_9_170"><span class="label">[9]</span></a> In this eruption, 36,380 human beings perished, of whom 37 were +Europeans; 163 villages (<i>kampoengs</i>) were entirely, and 132 partially, +destroyed.—Verbeek, <i>loc. cit.</i>, p. 79.</p></div> + +<div class="footnote"><p><a name="Footnote_10_171" id="Footnote_10_171"></a><a href="#FNanchor_10_171"><span class="label">[10]</span></a> Verbeek, <i>loc. cit.</i>, p. 144-5. The dust put a girdle round the earth +in thirteen days.</p></div> + +<div class="footnote"><p><a name="Footnote_11_172" id="Footnote_11_172"></a><a href="#FNanchor_11_172"><span class="label">[11]</span></a> Verbeek, <i>loc. cit.</i>, p. 30.</p></div> +<p><span class="pagenum"><a name="Page_217" id="Page_217">[Pg 217]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_VI_CHAPTER_II" id="PART_VI_CHAPTER_II"></a>CHAPTER II. +<br /><br /> +EARTHQUAKES.</h2> + + +<p><i>Connection of Earthquakes with Volcanic Action.</i>—The +connection between earthquake shocks and +volcanic eruptions is now so generally recognised +that it is unnecessary to insist upon it here. All +volcanic districts over the globe are specially liable +to vibrations of the crust; but at the same time it is +to be recollected that these movements visit countries +occasionally from which volcanoes, either recent or +extinct, are absent; in which cases we may consider +earthquake shocks to be abortive attempts to originate +volcanic action.</p> + +<p>(<i>a.</i>) <i>Origin.</i>—From the numerous observations +which have been made regarding the nature of these +phenomena by Hopkins, Lyell, and others, it seems +clearly established that earthquakes have their origin +in some sudden impact of gas, steam, or molten matter +impelled by gas or steam under high pressure, beneath +the solid crust.<a name="FNanchor_1_173" id="FNanchor_1_173"></a><a href="#Footnote_1_173" class="fnanchor">[1]</a> How such impact originates we need +<span class="pagenum"><a name="Page_218" id="Page_218">[Pg 218]</a></span>not stop to inquire, as the cause is closely connected +with that which produces volcanic eruptions. The +effect, however, of such impact is to originate a wave +of translation through the crust, travelling outwards +from the point, or focus, on the surface immediately +over the point of impact.<a name="FNanchor_2_174" id="FNanchor_2_174"></a><a href="#Footnote_2_174" class="fnanchor">[2]</a> These waves of translation +can in some cases be laid down on a map, and +are called "isoseismal curves," each curve representing +approximately an equal degree of seismal intensity; +as shown on the chart of a part of North America +affected by the great Charleston earthquake. (<a href="#FIGURE_37">Fig. 37</a>.) +Mr. Hopkins has shown that the earthquake-wave, +when it passes through rocks differing in density and +elasticity, changes in some degree not only its velocity, +but its direction; being both refracted and reflected +in a manner analogous to that of light when it passes +from one medium to another of different density.<a name="FNanchor_3_175" id="FNanchor_3_175"></a><a href="#Footnote_3_175" class="fnanchor">[3]</a> +When a shock traverses the crust through a thickness +of several miles it will meet with various kinds of rock +as well as with fissures and plications of the strata, +owing to which its course will be more or less modified.</p> + +<p>(<i>b.</i>) <i>Formation of Fissures.</i>—During earthquake +movements, fissures may be formed in the crust, and +filled with gaseous or melted matter which may not +in all cases reach the surface; and, on the principle +that volcanoes are safety-valves for regions beyond +their immediate influence, we may infer that the earthquake +shock, which generally precedes the outburst of +<span class="pagenum"><a name="Page_219" id="Page_219">[Pg 219]</a></span>a volcano long dormant, finds relief by the eruption +which follows; so that whatever may be the extent of +the disastrous results of such an eruption, they would +be still more disastrous if there had been no such +safety-valve as that afforded by a volcanic vent. Thus, +probably, owing to the extinction of volcanic activity +in Syria, the earthquakes in that region have been +peculiarly destructive. For example, on January 1, +1837, the town of Safed west of the Jordan valley was +completely destroyed by an earthquake in which most +of the inhabitants perished. The great earthquakes +of Aleppo in the present century, and of Syria in the +middle of the eighteenth, were of exceptional severity. +In that of Syria, which took place in 1759, and which +was protracted during a period of three months, an +area of 10,000 square leagues was affected. Accon, +Saphat, Baalbeck, Damascus, Sidon, Tripoli, and other +places were almost entirely levelled to the ground; +many thousands of human beings lost their lives.<a name="FNanchor_4_176" id="FNanchor_4_176"></a><a href="#Footnote_4_176" class="fnanchor">[4]</a> +Other examples might be cited.</p> + +<p>(<i>c.</i>) <i>Earthquake Waves.</i>—We have now to return to +the phenomena connected with the transmission of +earthquake-waves. The velocity of transmission +through the earth is very great, and several attempts +have been made to measure this velocity with accuracy. +The most valuable of such attempts are those connected +with the Charleston and Riviera shocks. Fortunately, +owing to the perfection of modern appliances, and the +number of observers all over the globe, these results +are entitled to great confidence. The phenomena +connected with the Charleston earthquake, which took +<span class="pagenum"><a name="Page_220" id="Page_220">[Pg 220]</a></span>place on the 31st of August, 1886, are described in +great detail by Captain Clarence E. Dutton, of the +U.S. Ordnance Corps.<a name="FNanchor_5_177" id="FNanchor_5_177"></a><a href="#Footnote_5_177" class="fnanchor">[5]</a> The conclusions arrived at +are;—that as regards the depth of the focal point, this is +estimated at twelve miles, with a probable error of less +than two miles; while, as regards the rate of travel of +the earthquake-wave, the estimate is (in one case) +about 3.236 miles per second; and in another about +3.226 miles per second.</p> + +<p>On the other hand, in the case of the earthquake of +the Riviera, which took place on the 23rd of February, +1887, at 5.30 a.m. (local time), the vibrations of which +appear to have extended across the Atlantic, and to +have sensibly affected the seismograph in the Government +Signal Office at Washington, the rate of travel +was calculated at about 500 miles per hour, less than +one-half that determined in the case of Charleston; +but Captain Dutton claims, and probably with justice, +that the results obtained in the latter case are far +more reliable than any hitherto arrived at.</p> + +<p>(<i>d.</i>) <i>Oceanic Waves.</i>—When the originating impact +takes place under the bed of the ocean—either by a +sudden up-thrust of the crust to the extent, let us +suppose, of two or three feet, or by an explosion from +a submarine volcano—a double wave is formed, one +travelling through the crust, the other through the +ocean; and as the rate of velocity of the former is +greatly in excess of that of the latter, the results on +their reaching the land are often disastrous in the +extreme. It is the ocean-wave, however, which is the +more important, and calls for special consideration. If +the impact takes place in very deep water, the whole +mass of the water is raised in the form of a low dome, +<span class="pagenum"><a name="Page_221" id="Page_221">[Pg 221]</a></span>sloping equally away in all directions; and it commences +to travel outwards as a wave with an advancing +crest until it approaches the coast and enters +shallow water. The wave then increases in height, +and the water in front is drawn in and relatively +lowered; so that on reaching a coast with a shelving +shore the form of the surface consists of a trough in +front followed by an advancing crest. These effects +may be observed on a small scale in the case of a +steamship advancing up a river, or into a harbour +with a narrow channel, but are inappreciable in deep +water, or along a precipitous open coast.</p> + +<p>(<i>e.</i>) <i>The Earthquake of Lisbon, 1755.</i>—The disastrous +results of a submarine earthquake upon the +coast have never been more terribly illustrated than +in the case of the earthquake of Lisbon which took +place on November 1, 1755. The inhabitants had no +warning of the coming danger, when a sound like +that of thunder was heard underground, and immediately +afterwards a violent shock threw down the +greater part of their city; this was the land-wave. In the +course of about six minutes, sixty thousand persons +perished. The sea first retired and left the harbour dry, +so forming the trough in front of the crest; immediately +after the water rolled in with a lofty crest, some 50 +feet above the ordinary level, flooding the harbour and +portions of the city bordering the shore. The mountains +of Arrabida, Estrella, Julio, Marvan, and Cintra, +were impetuously shaken, as it were, from their very +foundations; and according to the computation of +Humboldt, a portion of the earth's surface four times +the extent of Europe felt the effects of this great +seismic shock, which extended to the Alps, the shores +of the Baltic, the lakes of Scotland, the great lakes of +<span class="pagenum"><a name="Page_222" id="Page_222">[Pg 222]</a></span>North America, and the West Indian Islands. The +velocity of the sea-wave was estimated at about 20 +miles per minute.</p> + +<p>(<i>f.</i>) <i>Earthquake of Lima and Callao, 28th October, +1746.</i>—Of somewhat similar character was the terrible +catastrophe with which the cities of Lima and Callao +were visited in the middle of the last century,<a name="FNanchor_6_178" id="FNanchor_6_178"></a><a href="#Footnote_6_178" class="fnanchor">[6]</a> in +which the former city, then one of great magnificence, +was overthrown; and Callao was inundated by +a sea-wave, in which out of 23 ships of all sizes in the +harbour the greater number foundered; several, including +a man-of-war, were lifted bodily and stranded, +and all the inhabitants with the exception of about +two hundred were drowned. A volcano in Lucanas +burst forth the same night, and such quantities of +water descended from the cone that the whole +country was overflowed; and in the mountain near +Pataz, called Conversiones de Caxamarquilla, three +other volcanoes burst forth, and torrents of water +swept down their sides. In the case of these cities, +the land-wave, or shock, preceded the sea-wave, which +of course only reached the port of Callao.</p> + +<p><span class="pagenum"><a name="Page_223" id="Page_223">[Pg 223]</a></span></p> + +<div class="figcenter"> +<a name="FIGURE_37"> + <img src="images/figure37.jpg" alt="Isoseismal curves" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 37.</span>—The lines represent isoseismal curves, or curves of equal +intensity, the force decreasing outwards from the focus at Charleston, +No. 10. +</td></tr> +</table> +</div> + +<p>(<i>g.</i>) <i>Earthquake of Charleston, 31st August, 1886.</i>—I +shall close this account of some remarkable earthquakes +with a few facts regarding that of Charleston, +on the Atlantic seaboard of Carolina.<a name="FNanchor_7_179" id="FNanchor_7_179"></a><a href="#Footnote_7_179" class="fnanchor">[7]</a> At 9.51 a.m. +of this day, the inhabitants engaged in their ordinary +occupations were startled by the sound of a distant +roar, which speedily deepened in volume so as to resemble +the noise of cannon rattling along the road, +"spreading into an awful noise, that seemed to pervade +at once the troubled earth below and the still air +above." At the same time the floors began to heave +underfoot, the walls visibly swayed to and fro, and the +crash of falling masonry was heard on all sides, while +<span class="pagenum"><a name="Page_224" id="Page_224">[Pg 224]</a></span>universal terror took possession of the populace, who +rushed into the streets, the black portion of the community +being the most demonstrative of their terror. +Such was the commencement of the earthquake, by +which nearly all the houses of Charleston were damaged +or destroyed, many of the public buildings seriously +injured or partially demolished. The effects were felt +all over the States as far as the great lakes of Canada +and the borders of the Rocky Mountains. Two +epicentral <i>foci</i> appear to have been established; one +lying about 15 miles to the N.W. of Charleston, called +the <i>Woodstock focus</i>; the other about 14 miles due +west of Charleston, called the <i>Rantowles focus</i>; +around each of these <i>foci</i> the isoseismic curves concentrated,<a name="FNanchor_8_180" id="FNanchor_8_180"></a><a href="#Footnote_8_180" class="fnanchor">[8]</a> +but in the map (<a href="#FIGURE_37">Fig. 37</a>) are combined +into the area of one curve. The position of these <i>foci</i> +clearly shows that the origin of the Charleston earthquake +was not submarine, though occurring within a +short distance of the Atlantic border; the curves of +equal intensity (isoseismals) are drawn all over the +area influenced by the shock.</p> + +<p>As a general result of these detailed observations, +Captain Dutton states that there is a remarkable +coincidence in the phenomena with those indicated by +the theory of wave-motion as the proper one for an +elastic, nearly homogeneous, solid medium, composed +of such materials as we know to constitute the rocks +of the outer portions of the earth; but on the other +hand he states that nothing has been disclosed which +seems to bring us any nearer to the precise nature of +the forces which generated the disturbance.<a name="FNanchor_9_181" id="FNanchor_9_181"></a><a href="#Footnote_9_181" class="fnanchor">[9]</a></p> + +<div class="footnote"><p><a name="Footnote_1_173" id="Footnote_1_173"></a><a href="#FNanchor_1_173"><span class="label">[1]</span></a> The views of Mr. R. Mallet, briefly stated, are somewhat as +follows:—Owing to the secular cooling of the earth, and the consequent +lateral crushing of the surface, this crushing from time to +time overcomes the resistance; in which case shocks are experienced +along the lines of fracture and faulting by which the crust is intersected. +These shocks give rise to earthquake waves, and as the crushing of the +walls of the fissure developes heat, we have here the <i>vera causa</i> both of +volcanic eruptions and earthquake shocks—the former intensified into +explosions by access of water through the fissures.—"On the Dynamics +of Earthquakes," <i>Trans. Roy. Irish Acad.</i>, vol. xxi.</p></div> + +<div class="footnote"><p><a name="Footnote_2_174" id="Footnote_2_174"></a><a href="#FNanchor_2_174"><span class="label">[2]</span></a> Illustration of the mode of propagation of earthquake shocks will +be found in Lyell's <i>Principles of Geology</i>, vol. ii. p. 136, or in the +author's <i>Physiography</i>, p. 76, after Hopkins.</p></div> + +<div class="footnote"><p><a name="Footnote_3_175" id="Footnote_3_175"></a><a href="#FNanchor_3_175"><span class="label">[3]</span></a> "Rep. on Theories of Elevation and Earthquakes," <i>Brit. Ass. +Rep.</i> 1847, p. 33. In the map prepared by Prof. J. Milne and Mr. W. +K. Burton to show the range of the great earthquake of Japan (1891), +similar isoseismal lines are laid down.</p></div> + +<div class="footnote"><p><a name="Footnote_4_176" id="Footnote_4_176"></a><a href="#FNanchor_4_176"><span class="label">[4]</span></a> Lyell, <i>loc. cit.</i>, p. 163. Two Catalogues of Earthquakes have been +drawn up by Prof. O'Reilly, and are published in the <i>Trans. Roy. Irish +Academy</i>, vol. xxviii. (1884 and 1886).</p></div> + +<div class="footnote"><p><a name="Footnote_5_177" id="Footnote_5_177"></a><a href="#FNanchor_5_177"><span class="label">[5]</span></a> <i>Ninth Annual Report, U.S. Geological Survey</i> (1888).</p></div> + +<div class="footnote"><p><a name="Footnote_6_178" id="Footnote_6_178"></a><a href="#FNanchor_6_178"><span class="label">[6]</span></a> <i>A True and Particular Account of the Dreadful Earthquake</i>, 2nd +edit. The original published at Lima by command of the Viceroy. +London, 1748. Translated from the Spanish.</p></div> + +<div class="footnote"><p><a name="Footnote_7_179" id="Footnote_7_179"></a><a href="#FNanchor_7_179"><span class="label">[7]</span></a> I take the account from that of Capt. Dutton above cited, <a href="#Page_220">p. 220</a>.</p></div> + +<div class="footnote"><p><a name="Footnote_8_180" id="Footnote_8_180"></a><a href="#FNanchor_8_180"><span class="label">[8]</span></a> Dutton, <i>Report</i>, Plate xxvi., p. 308.</p></div> + +<div class="footnote"><p><a name="Footnote_9_181" id="Footnote_9_181"></a><a href="#FNanchor_9_181"><span class="label">[9]</span></a> <i>Ibid.</i>, p. 211. On the connection between the moon's position and +earthquake shocks, see Mr. Richardson's paper on Scottish earthquakes, +<i>Trans. Edin. Geol. Soc.</i>, vol. vi. p. 194 (1892).</p></div> +<p><span class="pagenum"><a name="Page_225" id="Page_225">[Pg 225]</a></span></p> + + +<hr class="major" /> +<h1><a name="PART_VII" id="PART_VII"></a>PART VII. +<br /><br /> +VOLCANIC AND SEISMIC PROBLEMS.</h1> + + + +<hr class="major" /> +<h2><a name="PART_VII_CHAPTER_I" id="PART_VII_CHAPTER_I"></a>CHAPTER I. +<br /><br /> +THE ULTIMATE CAUSE OF VOLCANIC ACTION.</h2> + + +<p>Volcanic phenomena are the outward manifestations +of forces deep-seated beneath the crust of the +globe; and in seeking for the causes of such phenomena +we must be guided by observation of their +nature and mode of action. The universality of these +phenomena all over the surface of our globe, in past +or present times, indicates the existence of a general +cause beneath the crust. It is true that there are +to be found large tracts from which volcanic rocks +(except those of great geological antiquity) are +absent, such as Central Russia, the Nubian Desert, +and the Central States of North America; but such +absence by no means implies the non-existence of +the forces which give rise to volcanic action beneath +those regions, but only that the forces have not been +sufficiently powerful to overcome the resistance offered +by the crust over those particular tracts. On the +other hand, the similarity of volcanic lavas over wide +regions is strong evidence that they are drawn from +<span class="pagenum"><a name="Page_226" id="Page_226">[Pg 226]</a></span>one continuous magma, consisting of molten matter +beneath the solid exterior crust.</p> + +<p>(<i>a.</i>) <i>Lines of Volcanic Action.</i>—It has been shown in a +previous page that volcanic action of recent or Tertiary +times has taken place mainly along certain lines which +may be traced on the surface of a map or globe. One +of these lines girdles the whole globe, while others lie +in certain directions more or less coincident with lines +of flexure, plication or faulting. The Isle of Sumatra +offers a remarkable example of the coincidence of +such lines with those of volcanic vents. Not only the +great volcanic cones, but also the smaller ones, are +disposed in chains which run parallel to the longitudinal +axis of the island (N.W.-S.E.). The sedimentary +rocks are bent and faulted in lines parallel +to the main axis, and also to the chains of volcanic +mountains, and the observation holds good with +regard to different geological periods.<a name="FNanchor_1_182" id="FNanchor_1_182"></a><a href="#Footnote_1_182" class="fnanchor">[1]</a> Another +remarkable case is that of the Jordan Valley. Nowhere +can the existence of a great fracture and +vertical displacement of the strata be more clearly +determined than along this remarkable line of depression; +and it is one which is also coincident with a +zone of earthquake and volcanic disturbances.</p> + +<p>(<i>b.</i>) <i>Such Lines generally lie along the Borders of the +Ocean.</i>—But even where, from some special cause, +actual observation on the relations of the strata are +precluded, the general configuration of the ground +and the relations of the boundaries between land and +sea to those of volcanic chains, evidently point in +many cases to their mutual interdependence. The +remarkable straightness of the coast of Western +<span class="pagenum"><a name="Page_227" id="Page_227">[Pg 227]</a></span>America, and of the parallel chain of the Andes, +affords presumptive evidence that this line is coincident +with a fracture or system of faults, along which +the continent has been bodily raised out of the waters +of the ocean. Of this elevation within very recent times +we have abundant evidence in the existence of raised +coral-reefs and oceanic shell-beds at intervals all along +the coast; rising in Peru to a level of no less than +3,000 feet above the ocean, as shown by Alexander +Agassiz.<a name="FNanchor_2_183" id="FNanchor_2_183"></a><a href="#Footnote_2_183" class="fnanchor">[2]</a> Such elevations probably occurred at a +time when the volcanoes of the Andes were much +more active than at present. Considered as a whole, +these great volcanic mountains may be regarded as +in a dormant, or partially moribund, condition; and +if the volcanic forces have to some extent lost their +strength, so it would appear have those of elevation.</p> + +<p>(<i>c.</i>) <i>Areas of Volcanic Action in the British Isles.</i>—In +the case of the British Islands it may be observed +that the later Tertiary volcanic districts lie along +very ancient depressions, which may indicate zones +of weakness in the crust. Thus the Antrim plateau, +as originally constituted, lay in the lap of a range of +hills formed of crystalline, or Lower Silurian, rocks; +while the volcanic isles of the Inner Hebrides were +enclosed between the solid range of the Archæan +rocks of the Outer Hebrides on the one side, and the +Silurian and Archæan ranges of the mainland on +the other. And if we go back to the Carboniferous +period, we find that the volcanic district of the centre +of Scotland was bounded by ranges of solid strata +both to the north and south, where the resistance to +interior pressure from molten matter would have +been greater than in the Carboniferous hollow-ground, +<span class="pagenum"><a name="Page_228" id="Page_228">[Pg 228]</a></span>where such molten matter has been abundantly extruded. +In all these cases, the outflow of molten +matter was in a direction somewhat parallel to the +plications of the strata.</p> + +<p>(<i>d.</i>) <i>Special Conditions under which the Volcanic +Action operates.</i>—Assuming, then, that the molten +matter, forming an interior magma or shell, is constantly +exerting pressure against the inner surface of +the solid crust, and can only escape where the crust +is too weak (owing to faults, plications, or fissures) to +resist the pressure, we have to inquire what are the +special conditions under which outbursts of volcanic +matter take place, and what are the general results +as regards the nature of the <i>ejecta</i> dependent on +those conditions.</p> + +<p>(<i>e.</i>) <i>Effect of the Presence or Absence of Water.</i>—The +two chief conditions determining the nature of +volcanic products, considered in the mass, are the +presence or absence of water. Such presence or +absence does not of course affect the essential +chemical composition of the <i>ejecta</i>, but it materially +influences the form in which the matter is erupted. +The agency of water in volcanic eruptions is a very +interesting and important subject in connection with +the history of volcanic action, and has been ably +treated by Professor Prestwich.<a name="FNanchor_3_184" id="FNanchor_3_184"></a><a href="#Footnote_3_184" class="fnanchor">[3]</a> At one time it was +considered that water was essential to volcanic +activity; and the fact that the great majority of +volcanic cones are situated in the vicinity of the +oceanic waters, or of inland seas, was pointed to in +confirmation of this theory. But the existence in +Western America and other volcanic countries of +fissures of eruption along which molten lava has been +<span class="pagenum"><a name="Page_229" id="Page_229">[Pg 229]</a></span>extruded without explosions of steam, shows that +water is not an essential factor in the production of +volcanic phenomena; and, as Professor Prestwich has +clearly demonstrated, it is to be regarded as an element +in volcanic explosions, rather than as a prime cause +of volcanic action. The main difficulty he shows to +be thermo-dynamical; and calculating the rate of +increase in the elastic force of steam on descending +to greater and greater depths and reaching strata +of higher and higher temperatures, as compared with +the force of capillarity, he comes to the conclusion +that water cannot penetrate to depths of more than +seven or eight miles, and therefore cannot reach the +seat of the eruptive forces. Professor Prestwich also +points out that if the extrusion of lava were due to +the elastic force of vapour of water there should be a +distinct relation between the discharge of the lava +and of the vapour; whereas the result of an examination +of a number of well-recorded eruptions shows that +the two operations are not related, and are, in fact, +perfectly independent. Sometimes there has been a +large discharge of lava, and little or no escape of +steam; at other times there have been paroxysmal +explosive eruptions with little discharge of lava. +Even in the case of Vesuvius, which is close to the sea, +there have been instances when the lava has welled +out almost with the tranquillity of a water-spring.</p> + +<p>(<i>f.</i>) <i>Access of Surface Water to Molten Lava during +Eruptions.</i>—The existence of water during certain +stages in eruptions is too frequent a phenomena to +be lost sight of; but its presence may be accounted +for in other ways, besides proximity to the sea or +ocean. Certain volcanic mountains, such as Etna +and Vesuvius, are built upon water-bearing strata, +<span class="pagenum"><a name="Page_230" id="Page_230">[Pg 230]</a></span>receiving their supplies from the rainfall of the surrounding +country, or perhaps partly from the sea. +In addition to this the ashes and scoriæ of the +mountain sides are highly porous, and rain or snow +can penetrate and settle downwards around the pipe +or throat through which molten lava wells up from +beneath. In such cases it is easy to understand how, +at the commencement of a period of activity, molten +lava ascending through one or more fissures, and +meeting with water-charged strata or scoriæ, will convert +the water into steam at high pressure, resulting +in explosions more or less violent and prolonged, in +proportion to the quantity of water and the depth +to which it has penetrated. In this manner we may +suppose that ashes, scoriæ, and blocks of rock torn +from the sides of the crater-throat, and hurled into +the air, are piled around the vent, and accumulate into +hills or mountains of conical form. After the explosion +has exhausted itself, the molten lava quietly +wells up and fills the crater, as in the cases of those of +Auvergne and Syria, and other places. We may, +therefore, adopt the general principle that in volcanic +eruptions <i>where water in large quantities is present, we +shall have crater-cones built up of ashes, scoriæ, and +pumice; but where absent, the lava will be extravasated +in sheets to greater or less distances without the formation +of such cones; or if cones are fanned, they will +be composed of solidified lava only, easily distinguishable +from crater-cones of the first class</i>.</p> + +<p>(<i>g.</i>) <i>Nature of the Interior Reservoir from which +Lavas are derived.</i>—We have now to consider the +nature of the interior reservoir from which lavas are +derived, and the physical conditions necessary for +their eruption at the surface.</p> + +<p><span class="pagenum"><a name="Page_231" id="Page_231">[Pg 231]</a></span></p><p>Without going back to the question of the original +condition of our globe, we may safely hold the view +that at a very early period of geological history it +consisted of a solidified crust at a high temperature, +enfolding a globe of molten matter at a still higher +temperature. As time went on, and the heat +radiated into space from the surface of the globe, +while at the same time slowly ascending from the +interior by conduction, the crust necessarily contracted, +and pressing more and more on the interior +molten magma, this latter was forced from time to +time to break through the contracting crust along +zones of weakness or fissures.</p> + +<p>(<i>h.</i>) <i>The Earth's Crust in a State of both Exterior +Thrust and of Interior Tension.</i>—As has been shown +by Hopkins,<a name="FNanchor_4_185" id="FNanchor_4_185"></a><a href="#Footnote_4_185" class="fnanchor">[4]</a> and more recently by Mr. Davison,<a name="FNanchor_5_186" id="FNanchor_5_186"></a><a href="#Footnote_5_186" class="fnanchor">[5]</a> an +exterior crust in such a condition must eventually +result in being under a state of horizontal thrust +towards the exterior and of tension towards the +interior surface. For the exterior portion, having +cooled down, and consequently contracted to its +normal state, will remain rigid up to a certain point +of resistance; but the interior portion still continuing +to contract, owing to the conduction of the heat +towards the exterior, would tend to enter upon a +condition of tension, as becoming too small for the interior +molten magma; and such a state of tension would +tend to produce rupture of the interior part. In this +manner fissures would be formed into which the +molten matter would enter; and if the fissures happened +to extend to the surface, owing to weakness of +the crust or flexuring of the strata, or other cause, the +<span class="pagenum"><a name="Page_232" id="Page_232">[Pg 232]</a></span>molten matter would be extruded either in the form +of dykes or volcanic vents. In this way we may +account for the numerous dykes of trap by which +some volcanic districts are intersected, such as those +of the north of Ireland and centre of Scotland.</p> + +<p>From the above considerations, it follows that the +earth's crust must be in a condition both of pressure +(or lateral thrust) towards the exterior portion, and +of tension towards the interior, the former condition +resulting in faulting and flexuring of the rocks, the +latter in the formation of open fissures, through which +lava can ascend under high pressure. These operations +are of course the attempt of the natural forces +to arrive at a condition of equilibrium, which is never +attained because the processes are never completed; +in other words, radiation and convection of heat are +constantly proceeding, giving rise to new forces of +thrust and tension.</p> + +<p>It now remains for us to consider what may be the +condition of the interior molten magma; and in doing +so we must be guided to a large extent by considerations +regarding the nature of the extruded matter at +the surface.</p> + +<p>(<i>i.</i>) <i>Relative Densities of Lavas.</i>—Now, observation +shows that, as bearing on the subject under consideration, +lavas occur mainly under two classes as regards +their density. The most dense (or basic) are those in +which silica is deficient, but iron is abundant; the +least dense (or acid) are those which are rich in silica, +but in which iron occurs in small quantity. This +division corresponds with that proposed by Bunsen +and Durocher<a name="FNanchor_6_187" id="FNanchor_6_187"></a><a href="#Footnote_6_187" class="fnanchor">[6]</a> for volcanic rocks, upon the results of +analyses of a large number of specimens from various +districts. Rocks may be thus arranged in groups:</p> +<p><span class="pagenum"><a name="Page_233" id="Page_233">[Pg 233]</a></span></p> + +<blockquote style="margin-left:10em; text-indent:-6em;"><p>(1) <i>The Basic</i> (Heavier)—poor in silica, rich in iron; containing +silica 45-58 per cent. Examples: +Basalt, Dolerite, Hornblende rock, Diorite, +Diabase, Gabbro, Melaphyre, and Leucite +lava.</p> + +<p>(2) <i>The Acid</i> (Lighter)—rich in silica, poor in iron; containing +silica 62-78 per cent. Examples: +Trachyte, Rhyolite, Obsidian, Domite, Felsite, +Quartz-porphyry, Granite.</p></blockquote> + +<p>The Andesite group forms a connecting link between +the highly acid and the basic groups, and there are +many varieties of the above which it is not necessary +to enumerate. Durocher supposes that the molten +magmas of these various rocks are arranged in concentric +shells within the solid crust in order of their +respective densities, those of the lighter density, +namely the acid magmas, being outside those of +greater density, namely the basic; and this is a view +which seems not improbable from a consideration not +only of the principle itself, but of the succession of +the varieties of lava in many districts. Thus we find +that acid lavas have been generally extruded first, and +basic afterwards—as in the cases of Western America, +of Antrim, the Rhine and Central France. And +if the interior of our globe had been in a condition +of equilibrium from the time of the consolidation +of the crust to the present, reason would +induce us to conclude that the lavas would ultimately +have arranged themselves in accordance with the +conditions of density beneath that crust. But the +state of equilibrium has been constantly disturbed. +Every fresh outburst of volcanic force, and every fresh +extrusion of lava, tends to disturb it, and to alter the +relations of the interior viscous or molten magmas. +Owing to this it happens, as we may suppose, that the +<span class="pagenum"><a name="Page_234" id="Page_234">[Pg 234]</a></span>order of eruption according to density is sometimes +broken, and we find such rocks as granophyre (a +variety of andesite) breaking through the plateau-basalts +of Mull and Skye, as explained in a former +chapter. Notwithstanding such variations, however, +the view of Durocher may be considered as the most +reasonable we can arrive at on a subject which is +confessedly highly conjectural.</p> + +<p>(<i>j.</i>) <i>Conclusion as regards the Ultimate Cause of +Volcanic Action</i>.—Notwithstanding, however, the complexity +of the subject, and the uncertainties which +must attend an inquiry where some of the data are outside +the range of our observation, sufficient evidence +can be adduced to enable us to arrive at a tolerably +clear view of the ultimate cause of volcanic action. +So tempting a subject was sure to evoke numerous +essays, some of great ingenuity, such as that of Mr. +Mallet; others of great complexity, such as that of +Dr. Daubeny. But more recent consideration and +wider observation have tended to lead us to the conclusion +that the ultimate cause is the most simple, the +most powerful, and the most general which can be +suggested; namely, <i>the contraction of the crust due to +secular cooling of the more deeply seated parts by conduction +and radiation of heat into space</i>. Owing to +this cause, the enclosed molten matter is more or less +abundantly extruded from time to time along the +lines and vents of eruption, so as to accommodate itself +to the ever-contracting crust. Nor can we doubt that +this process has been going on from the very earliest +period of the earth's history, and formerly at a greater +rate than at present. When the crust was more +highly heated, the radiation and conduction must +have been proportionately more rapid. Owing to +<span class="pagenum"><a name="Page_235" id="Page_235">[Pg 235]</a></span>this cause also the contraction of the crust was +accelerated. To such irresistible force we owe +the wonderful flexuring, folding, and horizontal +overthrusting which the rocks have undergone in +some portions of the globe—such as in the Alps, the +Highlands of Scotland and of Ireland, and the Alleghannies +of America. It is easy to show that the +acceleration of the earth's rotation must be a consequence +of such contraction; but, after all, this is but +one of those compensatory forces of which we see +several examples in the world around us. It can also +be confidently inferred that at an early period of the +earth's history, when the moon was nearer to our +planet than at present, the tides were far more powerful, +and their effect in retarding the earth's rotation +was consequently greater. During this period the +acceleration due to contraction was also greater; and +the two forces probably very nearly balanced each +other. Both these forces (those of acceleration and +retardation) have been growing weaker down to the +present day, though there appears to have been a +slight advantage on the side of the retarding force.<a name="FNanchor_7_188" id="FNanchor_7_188"></a><a href="#Footnote_7_188" class="fnanchor">[7]</a></p> + +<div class="footnote"><p><a name="Footnote_1_182" id="Footnote_1_182"></a><a href="#FNanchor_1_182"><span class="label">[1]</span></a> R. D. M. Verbeek, <i>Krakatau</i>, p. 105 (1886); also, J. Milne, <i>The +Great Earthquake of Japan</i>, 1891.</p></div> + +<div class="footnote"><p><a name="Footnote_2_183" id="Footnote_2_183"></a><a href="#FNanchor_2_183"><span class="label">[2]</span></a> <i>Bull. Mus. Comp. Zool.</i>, vol. iii.</p></div> + +<div class="footnote"><p><a name="Footnote_3_184" id="Footnote_3_184"></a><a href="#FNanchor_3_184"><span class="label">[3]</span></a> <i>Proc. Roy. Soc.</i>, No. 237 (1885); also, <i>Rep. Brit. Assoc.</i> (1881).</p></div> + +<div class="footnote"><p><a name="Footnote_4_185" id="Footnote_4_185"></a><a href="#FNanchor_4_185"><span class="label">[4]</span></a> Hopkins, <i>supra cit.</i>, <a href="#Page_218">p. 218</a>.</p></div> + +<div class="footnote"><p><a name="Footnote_5_186" id="Footnote_5_186"></a><a href="#FNanchor_5_186"><span class="label">[5]</span></a> C. Davison and G. H. Darwin, <i>Phil. Trans.</i>, vol. 178, p; 241.</p></div> + +<div class="footnote"><p><a name="Footnote_6_187" id="Footnote_6_187"></a><a href="#FNanchor_6_187"><span class="label">[6]</span></a> Durocher, <i>Ann. des Mines</i>, vol. ii. (1857).</p></div> + +<div class="footnote"><p><a name="Footnote_7_188" id="Footnote_7_188"></a><a href="#FNanchor_7_188"><span class="label">[7]</span></a> See on this subject the author's <i>Textbook of Physiography</i> (Deacon +and Co., 1888), pp. 56 and 122.</p></div> +<p><span class="pagenum"><a name="Page_236" id="Page_236">[Pg 236]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_VII_CHAPTER_II" id="PART_VII_CHAPTER_II"></a>CHAPTER II. +<br /><br /> +LUNAR VOLCANOES.</h2> + + +<p>The surface of the moon presented to our view affords +such remarkable indications of volcanic phenomena +of a special kind, that we are justified in devoting a +chapter to their consideration. It is very tantalising +that our beautiful satellite only permits us to look at +and admire one half of her sphere; but it is not a very +far-fetched inference if we feel satisfied that the other +half bears a general resemblance to that which is presented +to the earth. It is scarcely necessary to inform +the reader why it is that we never see but one face; +still, for the sake of those who have not thought out +the subject I may state that it is because the moon +rotates on her axis exactly in the time that she performs +a revolution round the earth. If this should +not be sufficiently clear, let the reader perform a very +simple experiment for himself, which will probably +bring conviction to his mind that the explanation here +given is correct. Let him place an orange in the +centre of a round table, and then let him move +round the table from a starting-point sideways, ever +keeping his face directed towards the orange; and +when he has reached his starting-point, he will find +that he has rotated once round while he has performed +one revolution round the table. In this case the performer +<span class="pagenum"><a name="Page_237" id="Page_237">[Pg 237]</a></span>represents the moon and the orange the +earth.</p> + +<p>Now this connection between the earth and her +satellite is sufficiently close to be used as an argument +(if not as actual demonstration) that the earth and +the moon were originally portions of the same mass, +and that during some very early stage in the development +of the solar system these bodies parted company, +to assume for ever after the relations of planet and +satellite. At the epoch referred to, we may also suppose +that these two masses of matter were in a highly +incandescent, if not even gaseous, state; and we conclude, +therefore, that having been once portions of the +same mass, they are composed of similar materials. +This conclusion is of great importance in enabling us +to reason from analogy regarding the origin of the +physical features on the moon's surface, and for the +purpose of comparison with those which we find on +the surface of our globe; because it is evident that, if +the composition of the moon were essentially different +from that of our earth, we should have no basis whatever +for a comparison of their physical features.</p> + +<p>When the moon started on her career of revolution +round the earth, we may well suppose that her orbit was +much smaller than at present. She was influenced by +counteracting forces, those of gravitation drawing her +towards the centre of gravity of the earth,<a name="FNanchor_1_189" id="FNanchor_1_189"></a><a href="#Footnote_1_189" class="fnanchor">[1]</a> and the +centrifugal force, which in the first instance was the +stronger, so that her orbit for a lengthened period +gradually increased until the two forces, those of +<span class="pagenum"><a name="Page_238" id="Page_238">[Pg 238]</a></span>attraction and repulsion, came into a condition of +equilibrium, and she now performs her revolution +round the earth at a mean distance of 240,000 miles, +in an orbit which is only very slightly elliptical.<a name="FNanchor_2_190" id="FNanchor_2_190"></a><a href="#Footnote_2_190" class="fnanchor">[2]</a> How +the period of the moon's rotation is regulated by the +earth's attraction on her molten lava-sheets, first at the +surface, and now probably below the outer crust, has +been graphically shown by Sir Robert Ball,<a name="FNanchor_3_191" id="FNanchor_3_191"></a><a href="#Footnote_3_191" class="fnanchor">[3]</a> but it +cannot be doubted that once the moon was appreciably +nearer to our globe than at present. The attraction of +her mass produced tides in the ocean of correspondingly +greater magnitude, and capable of effecting +results, both in eroding the surface and in transporting +masses of rock, far beyond the bounds of our +every-day experience.</p> + +<p>Of all the heavenly bodies, the sun excepted, the +moon is the most impressive and beautiful. As we +catch her form, rising as a fair crescent in the western +sky after sunset, gradually increasing in size and +brilliancy night after night till from her circular disk +she throws a full flood of light on our world and then +passes through her decreasing phases, we recognise +her as "the Governor of the night," or in the words +of our own poet, when in her crescent phase, "the +Diadem of night." Seen through a good binocular glass, +her form gains in rotundity; but under an ordinary +telescope with a four-inch objective, she appears like a +globe of molten gold. Yet all this light is derivative, +and is only a small portion of that she receives from +the sun. That her surface is a mass of rigid matter +destitute of any inherent brilliancy, appears plain +<span class="pagenum"><a name="Page_239" id="Page_239">[Pg 239]</a></span>enough when we view a portion of her disk through +a very large telescope. It was the good fortune of +the author to have an opportunity for such a view +through one of the largest telescopes in the world. +The 27-inch refractor manufactured by Sir Howard +Grubb of Dublin, for the Vienna observatory, a few +years ago, was turned on a portion of the moon's +disk before being finally sent off to its destination; +and seen by the aid of such enormous magnifying +power, nothing could be more disappointing as regards +the appearance of our satellite. The sheen and lustre +of the surface was now observed no longer; the mountains +and valleys, the circular ridges and hollows +were, indeed, wonderfully defined and magnified, but +the matter of which they seemed to be constituted +resembled nothing so much as the pale plaster of a +model. One could thus fully realise the fact that the +moon's light is only derivative. Still we must recollect +that the most powerful telescope can only bring +the surface of the moon to a distance from us of +about 250 miles; and it need not be said that objects +seen at such a distance on our earth present very +deceptive appearances; so that we gain little information +regarding the composition of the moon's crust, +or exterior surface, simply from observation by the aid +of large telescopes.</p> + +<p>Reasoning from analogy with our globe, we may +infer that the exterior shell of the moon consists of +crystalline volcanic matter of the highly silicated, or +acid, varieties resting upon another of a denser description, +rich in iron, and resembling basalt. This +hypothesis is hazarded on the supposition that the +composition of the matter of the moon's mass resembles +in the main that of our globe. During the +<span class="pagenum"><a name="Page_240" id="Page_240">[Pg 240]</a></span>process of cooling from a molten condition, the heavier +lavas would tend to fall inwards, and allow the lighter +to come to the surface, and form the outer shell in +both cases. Thus, the outer crust would resemble the +trachytic lavas of our globe, and their pale colour +would enable the sun's rays to be reflected to a greater +extent than if the material were of the blackness of +basalt.<a name="FNanchor_4_192" id="FNanchor_4_192"></a><a href="#Footnote_4_192" class="fnanchor">[4]</a> So much for the material. We have now to +consider the structure of the moon's surface, and here +we find ourselves treading on less speculative and +safer ground. All astronomers since the time of +Schroter seem to be of accord in the opinion that the +remarkable features of the moon's surface are in some +measure of volcanic origin, and we shall presently +proceed to consider the character of these forms more +in detail.</p> + +<p>But first, and as leading up to the discussion of +these physical features, we must notice one essential +difference between the constitution of the moon and +of the earth; namely, the absence of water and of an +atmosphere in the case of the moon. The sudden and +complete occultation of the stars when the moon's disk +passes between them and the place of the observer on +the earth's surface, is sufficient evidence of the absence +of air; and, as no cloud has ever been noticed to veil +even for a moment any part of our satellite's face, we +are pretty safe in concluding that there is no water; +or at least, if there be any, that it is inappreciable in +<span class="pagenum"><a name="Page_241" id="Page_241">[Pg 241]</a></span>quantity.<a name="FNanchor_5_193" id="FNanchor_5_193"></a><a href="#Footnote_5_193" class="fnanchor">[5]</a> Hence we infer that there is no animal or +vegetable life on the moon's surface; neither are there +oceans, lakes or rivers, snowfields or glaciers, river-valleys +or cañons, islands, stratified rocks, nor volcanoes +of the kind most prevalent on our own +globe.</p> + +<div class="figcenter"> +<a name="FIGURE_38"></a> +<a href="images/figure38full.jpg"> + <img src="images/figure38.jpg" alt="Photograph of the Moon" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 38.</span>—Photograph of the moon's surface (in part) showing the +illuminated "spots," and ridges, and the deep hollows. The position +of "Tycho" is shown near the upper edge, and some of the volcanic +craters are very clearly seen near the margin. +</td></tr> +</table> +</div> + +<p><span class="pagenum"><a name="Page_242" id="Page_242">[Pg 242]</a></span></p><p>Now on looking at a photographic picture of the +moon's surface (<a href="#FIGURE_38">Fig. 38</a>), we observe that there are +enormous dark spaces, irregular in outline, but more or +less approaching the circular form, surrounded by steep +and precipitous declivities, but with sides sloping outwards. +These were supposed at one time to be seas; +and they retain the name, though it is universally +admitted that they contain no water. Some of these +hollows are four English miles in depth. The largest +of these, situated near the north pole of the moon, is +called <i>Mare Imbrium</i>; next to it is <i>Mare Serenitatis</i>; +next, <i>Mare Tranquilitatis</i>, with several others.<a name="FNanchor_6_194" id="FNanchor_6_194"></a><a href="#Footnote_6_194" class="fnanchor">[6]</a> Mare +Imbrium is of great depth, and from its floor rise +several conical mountains with circular craters, the +largest of which, <i>Archimedes</i>, is fifty miles in diameter; +its vast smooth interior being divided into seven +distinct zones running east and west. There is no +central mountain or other obvious internal sign of +former volcanic activity, but its irregular wall rises +into abrupt towers, and is marked outside by decided +terraces.<a name="FNanchor_7_195" id="FNanchor_7_195"></a><a href="#Footnote_7_195" class="fnanchor">[7]</a></p> + +<p>The Mare Imbrium is bounded along the east by a +range of mountains called the <i>Apennines</i>, and towards +the north by another range called the <i>Alps</i>; while a +third range, that of the <i>Caucasus</i>, strikes northward +from the junction of the two former ranges. Several +<span class="pagenum"><a name="Page_243" id="Page_243">[Pg 243]</a></span>circular or oval craters are situated on, and near to, +the crest of these ridges.</p> + +<div class="figcenter"> +<a name="FIGURE_39"> + <img src="images/figure39.jpg" alt="Portion of the Moon" /> +</a> +<table border="0" summary="" style="max-width:80%;"> +<tr><td align="left"> +<span class="smcap">Fig. 39.</span>—A magnified portion of the moon's surface, showing the +forms of the great craters with their outer ramparts. The white spot +with shadow is a cone rising from the centre of one of the larger craters +to a great height and thus becoming illuminated by the sun's light. +</td></tr> +</table> +</div> + +<p>But the greater part of the moon's hemisphere is +dotted over by almost innumerable circular crater-like +hollows; sometimes conspicuously surmounting lofty +conical mountains, at other times only sinking below +the general outer surface of the lunar sphere. On +approaching the margin, these circular hollows appear +oval in shape owing to their position on the sphere; +and the general aspect of those that are visible leads +to the conclusion that there are large numbers of +smaller craters too small to be seen by the most +powerful telescopes. These cones and craters are +<span class="pagenum"><a name="Page_244" id="Page_244">[Pg 244]</a></span>the most characteristic objects on the whole of the +visible surface, and when highly magnified present +very rugged outlines, suggestive of slag, or lava, +which has consolidated on cooling, as in the case of +most solidified lava-streams on our earth.<a name="FNanchor_8_196" id="FNanchor_8_196"></a><a href="#Footnote_8_196" class="fnanchor">[8]</a> One of +the most remarkable of these crateriform mountains +is that named <i>Copernicus</i>, situated in a line with the +southern prolongation of the Apennines. Of this +mountain Sir R. Ball says: "It is particularly well +known through Sir John Herschel's drawing, so +beautifully reproduced in the many editions of the +<i>Outlines of Astronomy</i>. The region to the west is +dotted over with innumerable minute craterlets. It +has a central, many-peaked mountain about 2,400 +feet in height. There is good reason to believe that +the terracing shown in its interior is mainly due to +the repeated alternate rise, partial congealation and +retreat of a vast sea of lava. At full moon it is +surrounded by radiating streaks."<a name="FNanchor_9_197" id="FNanchor_9_197"></a><a href="#Footnote_9_197" class="fnanchor">[9]</a> The view regarding +the structure of Copernicus here expressed is of +importance, as it is probably applicable to all the +craters of our satellite.</p> + +<p>"When the moon is five or six days old," says Sir +Robert Ball, "a beautiful group of three craters will +be readily found on the boundary line between night +and day. These are <i>Catharina</i>, <i>Cyrillus</i>, and <i>Theophilus</i>. +Catharina is the most southerly of the group, +and is more than 16,000 feet deep and connected to +Cyrillus by a wide valley; but between Cyrillus and +Theophilus there is no such connection. Indeed +Cyrillus looks as if its huge surrounding ramparts, +as high as Mont Blanc, had been completely finished +<span class="pagenum"><a name="Page_245" id="Page_245">[Pg 245]</a></span>when the volcanic forces commenced the formation of +Theophilus, the rampart of which encroaches considerably +on its older neighbour. Theophilus stands +as a well-defined round crater, about 64 miles in +diameter, with an internal depth of 14,000 to 18,000 +feet, and a beautiful central group of mountains, one-third +of that height, on its floor. This proves that the +last eruptive efforts in this part of the moon fully +equalled in intensity those that had preceded them. +Although Theophilus is on the whole the deepest +crater we can see in the moon, it has received little +or no deformation by secondary eruptions."</p> + +<p>But perhaps the most remarkable object on the +whole hemisphere of the moon is "the majestic +Tycho," which rises from the surface near the south +pole, and at a distance of about 1/6th of the diameter +of the sphere from its margin. Its depth is stated by +Ball to be 17,000 feet, and its diameter 50 miles. +But its special distinction amongst the other volcanic +craters lies in the streaks of light which radiate from +it in all directions for hundreds and even thousands of +miles, stretching with superb indifference across vast +plains, into the deepest craters, and over the highest +opposing ridges. When the sun rises on Tycho these +streaks are invisible, but as soon as it has reached a +height of 25° to 30° above the horizon, the rays emerge +from their obscurity, and gradually increase in brightness +until full moon, when they become the most conspicuous +objects on her surface. As yet no satisfactory +explanation has been given of the origin of these illuminated +rays,<a name="FNanchor_10_198" id="FNanchor_10_198"></a><a href="#Footnote_10_198" class="fnanchor">[10]</a> but I may be permitted to add that their +form and mode of occurrence are eminently suggestive +of gaseous exhalations from the volcano illumined by +<span class="pagenum"><a name="Page_246" id="Page_246">[Pg 246]</a></span>the sun's rays; and owing to the absence of an +atmosphere, spreading themselves out in all directions +and becoming more and more attenuated until they +cease to be visible.</p> + +<p>The above account will probably suffice to give the +reader a general idea of the features and inferential +structure of the moon's surface. That she was once +a molten mass is inferred from her globular form; +but, according to G. F. Chambers, the most delicate +measurements indicate no compression at the poles.<a name="FNanchor_11_199" id="FNanchor_11_199"></a><a href="#Footnote_11_199" class="fnanchor">[11]</a> +That her surface has cooled and become rigid is also +a necessary inference; though Sir J. Herschel considered +that the surface still retains a temperature +<i>possibly</i> exceeding that of boiling water.<a name="FNanchor_12_200" id="FNanchor_12_200"></a><a href="#Footnote_12_200" class="fnanchor">[12]</a> However +this may be, it is pretty certain that whatever changes +may occur upon her surface are not due to present +volcanic action, all evidence of such action being +admittedly absent. If, when the earth and moon +parted company, their respective temperatures were +equal, the moon being so much the smaller of the +two would have cooled more rapidly, and the surface +may have been covered by a rigid crust when as yet +that of the earth may have been molten from heat. +Hence the rigidity of the moon's surface may date +back to an immensely distant period, but she may +still retain a high temperature within this crust. +Having arrived at this stage of our narrative, we are +in a position to consider by what means, and under +what conditions, the cones and craters which diversify +the lunar surface have been developed.</p> + +<p>In doing so it may be desirable, in the first place, to +determine what form of crater on our earth's surface +those of the moon do not represent; and we are +<span class="pagenum"><a name="Page_247" id="Page_247">[Pg 247]</a></span>guided in our inquiry by the consideration of the +absence of water on the lunar surface. Now there +are large numbers of crateriform mountains on our +globe in the formation of which water has played an +important, indeed essential, part. As we have already +seen, water, though not the ultimate cause of volcanic +eruptions, has been the chief agent, when in the form +of steam at high pressure, in producing the explosions +which accompany these eruptions, and in tearing up +and hurling into the air the masses of rock, scoriæ, +and ashes, which are piled around the vents of eruption +in the form of craters during periods of activity. +To this class of craters those of Etna, Vesuvius, and +Auvergne belong. These mountains and conical hills +(the domes excepted) are all built up of accumulations +of fragmental material, with occasional sheets +and dykes of lava intervening; and where eruptions +have taken place in recent times, observation has +shown that they are accompanied by outbursts of +vast quantities of aqueous vapour, which has been the +chief agent (along with various gases) in piling up the +circular walls of the crater.</p> + +<p>It has also been shown that in many instances +these crater-walls have been breached on one side, +and that streams of molten lava which once occupied +the cup to a greater or less height, have poured down +the mountain side. Hence the form or outline of +many of these fragmental craters is crescent-shaped. +Such breached craters are to be found in all parts of +the world, and are not confined to any one district, or +even continent, so that they may be considered as +characteristic of the class of volcanic crater-cones to +which I am now referring. In the case of the moon, +however, we fail to observe any decided instances +<span class="pagenum"><a name="Page_248" id="Page_248">[Pg 248]</a></span>of breached craters, with lava-streams, such as those +I have described.<a name="FNanchor_13_201" id="FNanchor_13_201"></a><a href="#Footnote_13_201" class="fnanchor">[13]</a> In nearly all cases the ramparts +appear to extend continuously round the enclosed +depression, solid and unbroken; or at least with no +large gap occupying a very considerable section of the +circumference. (See <a href="#FIGURE_38">Fig. 38</a>.) Hence we are led to +suspect that there is some essential distinction between +the craters on the surface of the moon and the greater +number of those on the surface of our earth.</p> + +<p>It is scarcely necessary to add that the volcanic +mountains of the moon offer no resemblance whatever +to the dome-shaped volcanic mountains of our +globe. If it were otherwise, the lunar mountains +would appear as simple luminous points rising from a +dark floor, over which they would cast a conical +shadow. But the form of the lunar volcanic mountains +is essentially different; as already observed, +they consist in general of a circular rampart enclosing +a depressed floor, sometimes terraced as in the case of +Copernicus, from which rise one or more conical +mountains, which are in effect the later vents of +eruption.</p> + +<p>In our search, therefore, for analogous forms on our +own earth, we must leave out the craters and domes +of the type furnished by the European volcanoes and +their representatives abroad, and have recourse to +others of a different type. Is there then, we may ask, +any type of volcanic mountain on our globe comparable +with those on the moon? In all probability +there is.</p> + +<p>If the reader will turn to the description of the +<span class="pagenum"><a name="Page_249" id="Page_249">[Pg 249]</a></span>volcanoes of the Hawaiian group in the Pacific, +especially that of Mauna Loa, as given by Professor +Dana and others, and compare it with that of Copernicus, +he will find that in both cases we have a +circular rampart of solid lava enclosing a vast plain +of the same material from which rise one or more +lava-cones. The interiors in both cases are terraced. +So that, allowing for differences in magnitude, it would +seem that there is no essential distinction between +lunar craters and terrestrial craters of the type of +Mauna Loa. Dana calls these Hawaiian volcanoes +"basaltic," basalt being the prevalent material of +which they are formed. Those of the moon may be +composed of similar material, or otherwise; but in +either case we may suppose they are built up of +lava, erupted from vents connected with the molten +reservoirs of the interior. Thus we conclude that they +belong to an entirely different type, and have been +built up in a different manner, from those represented +by Etna, Vesuvius, and most of the extinct volcanoes +of Auvergne, the Eifel, and of other districts considered +in these pages.</p> + +<p>Let us now endeavour to picture to ourselves the +stages through which the moon may be supposed to +have passed from the time her surface began to consolidate +owing to the radiation of her heat into space; +for there is every probability that some of the craters +now visible on her disk were formed at a very early +period of her physical history.</p> + +<p>When the surface began to consolidate, it must +also have contracted; and the interior molten matter, +pressed out by the contracting crust, must have been +over and over again extruded through fissures produced +over the solidified surface, until the solid crust +<span class="pagenum"><a name="Page_250" id="Page_250">[Pg 250]</a></span>extended over the whole lunar surface, and became +of considerable thickness.</p> + +<p>It is from this epoch that, in all probability, we +should date the commencement of what may be +termed "the volcanic history" of the moon. We +must bear in mind that although the moon's surface +had become solid, its temperature may have remained +high for a very long period. But the continuous +radiation of the surface-heat into space would produce +continuous contraction, while the convection of the +interior heat would tend to increase the thickness of +the outer solid shell; and this, ever pressing with +increasing force on the interior molten mass, would +result in frequent ruptures of the shell, and the extrusion +of molten lava rising from below. Hence we +may suppose the fissure-eruptions of lava were of +frequent occurrence for a lengthened period during +the early stage of consolidation of the lunar crust; but +afterwards these may be supposed to have given place +to eruptions through pipes or vents, resulting in the +formation of the circular craters which form such +striking and characteristic objects in the physical +aspect of our satellite.<a name="FNanchor_14_202" id="FNanchor_14_202"></a><a href="#Footnote_14_202" class="fnanchor">[14]</a></p> + +<p>It is not to be supposed that the various physical +features on the lunar surface have all originated in +the same way. The great ranges of mountains previously +described may have originated by a process +of piling up of immense masses of molten lava +extruded from the interior through vents or fissures; +while the great hollows (or "seas") are probably +<span class="pagenum"><a name="Page_251" id="Page_251">[Pg 251]</a></span>due to the falling inwards of large spaces owing to +the escape of the interior lava.</p> + +<p>But it is with the circular craters that we are most +concerned. Judging from analogy with the lava-craters +present on our globe, we must suppose them +to be due to the extrusion, and piling up, of lava +through central pipes, followed in some cases by +the subsidence of the floor of the crater. It seems +not improbable that it was in this way the greater +number of the circular craters lying around Tycho, +and dotting so large a space round the margin of +the moon, were constructed. (See <a href="#FIGURE_38">Fig. 38</a>.) In +general they appear to consist of an elevated rim, +enclosing a depressed plain, out of which a central +cone arises. The rim may be supposed to have been +piled up by successive discharges of lava from a +central orifice; and after the subsidence of the +paroxysm the lava still in a molten condition may +have sunk down, forming a seething lake within the +vast circular rampart, as in the case of the Hawaiian +volcanoes. The terraces observable within the craters +in some instances have probably been left by subsequent +eruptions which have not attained to the level +of preceding ones; and where a central crater-cone is +seen to rise within the caldron, we may suppose this +to have been built up by a later series of eruptions of +lava through the original pipe after the consolidation +of the interior sea of lava. The mamelons of the +Isle of Bourbon,<a name="FNanchor_15_203" id="FNanchor_15_203"></a><a href="#Footnote_15_203" class="fnanchor">[15]</a> and some of the lava-cones of +Hawaii, appear to offer examples on our earth's +surface of these peculiar forms.</p> + +<p>Such are the views of the origin of the physical +<span class="pagenum"><a name="Page_252" id="Page_252">[Pg 252]</a></span>features of our satellite which their form and inferred +constitution appear to suggest. They are not offered +with any intention of dogmatising on a subject +which is admittedly obscure, and regarding which +we have by no means all the necessary data for +coming to a clear conclusion. All that can be +affirmed is, that there is a great deal to be said in +support of them, and that they are to some extent in +harmony with phenomena within range of observation +on the surface of our earth.</p> + +<p>The far greater effects of lunar vulcanicity, as compared +with those of our globe, may be accounted for +to some extent by the consideration that the force of +gravity on the surface of the moon is only one-sixth +of that on the surface of the earth. Hence the +eruptive forces of the interior of our satellite have +had less resistance to overcome than in the case of +our planet; and the erupted materials have been shot +forth to greater distances, and piled up in greater +magnitude, than with us. We have also to recollect +that the abrading action of water has been absent +from the moon; so that, while accumulations of matter +had been proceeding throughout a prolonged period +over its surface, there was no counteracting agency +of denudation at work to modify or lessen the effects +of the ruptive forces.</p> + +<div class="footnote"><p><a name="Footnote_1_189" id="Footnote_1_189"></a><a href="#FNanchor_1_189"><span class="label">[1]</span></a> Correctly speaking, each attracts the other towards its centre of +gravity with a force proportionate to its mass, and inversely as the +square of the distance; but the earth being by much the larger body, +its attraction is far greater than that of the moon.</p></div> + +<div class="footnote"><p><a name="Footnote_2_190" id="Footnote_2_190"></a><a href="#FNanchor_2_190"><span class="label">[2]</span></a> The variation in the distance is only under rare circumstances +40,000 miles, but ordinarily about 13,000 miles.</p></div> + +<div class="footnote"><p><a name="Footnote_3_191" id="Footnote_3_191"></a><a href="#FNanchor_3_191"><span class="label">[3]</span></a> <i>Story of the Heavens</i>, 2nd edition, p. 525, <i>et seq.</i></p></div> + +<div class="footnote"><p><a name="Footnote_4_192" id="Footnote_4_192"></a><a href="#FNanchor_4_192"><span class="label">[4]</span></a> A series of researches made by Zöllner, of Leipzig, led him to +assign to the light-reflecting capacity of the full-moon a result intermediate +between that obtained by Bouguer, which gave a brightness equal +to 1/300000 part of that of the sun, and of Wollaston, which gave 1/801070 +part. We may accept 1/618000 of Zöllner as sufficiently close; so that it +would require 600,000 full moons to give the same amount of light as +that of the sun.</p></div> + +<div class="footnote"><p><a name="Footnote_5_193" id="Footnote_5_193"></a><a href="#FNanchor_5_193"><span class="label">[5]</span></a> Schroter, however, came to the conclusion that the moon has an +atmosphere.</p></div> + +<div class="footnote"><p><a name="Footnote_6_194" id="Footnote_6_194"></a><a href="#FNanchor_6_194"><span class="label">[6]</span></a> A chart of the moon's surface, with the names of the principal +physical features, will be found in Ball's <i>Story of the Heavens</i>, 2nd +edit., p. 60. It must be remembered that the moon as seen through a +telescope appears in reversed position.</p></div> + +<div class="footnote"><p><a name="Footnote_7_195" id="Footnote_7_195"></a><a href="#FNanchor_7_195"><span class="label">[7]</span></a> <i>Ibid.</i>, p. 66.</p></div> + +<div class="footnote"><p><a name="Footnote_8_196" id="Footnote_8_196"></a><a href="#FNanchor_8_196"><span class="label">[8]</span></a> As represented by Nasmyth's models in plaster.</p></div> + +<div class="footnote"><p><a name="Footnote_9_197" id="Footnote_9_197"></a><a href="#FNanchor_9_197"><span class="label">[9]</span></a> Ball, <i>loc. cit.</i>, p. 67.</p></div> + +<div class="footnote"><p><a name="Footnote_10_198" id="Footnote_10_198"></a><a href="#FNanchor_10_198"><span class="label">[10]</span></a> Ball, <i>loc. cit.</i>, p. 69.</p></div> + +<div class="footnote"><p><a name="Footnote_11_199" id="Footnote_11_199"></a><a href="#FNanchor_11_199"><span class="label">[11]</span></a> <i>Astronomy</i>, p. 78.</p></div> + +<div class="footnote"><p><a name="Footnote_12_200" id="Footnote_12_200"></a><a href="#FNanchor_12_200"><span class="label">[12]</span></a> <i>Outlines of Astronomy</i>, p. 285.</p></div> + +<div class="footnote"><p><a name="Footnote_13_201" id="Footnote_13_201"></a><a href="#FNanchor_13_201"><span class="label">[13]</span></a> At rare intervals a few crescent-shaped ridges are discernible on the +lunar sphere, but it is very doubtful if they are to be regarded as +breached craters.</p></div> + +<div class="footnote"><p><a name="Footnote_14_202" id="Footnote_14_202"></a><a href="#FNanchor_14_202"><span class="label">[14]</span></a> The number of "spots" on the moon was considered to be 244 +until Schroter increased it to 6,000, and accurately described many of +them. Schroter seems to have been the earliest observer who identified +the circular hollows on the moon's surface as volcanic craters.</p></div> + +<div class="footnote"><p><a name="Footnote_15_203" id="Footnote_15_203"></a><a href="#FNanchor_15_203"><span class="label">[15]</span></a> Drawings of these very curious forms are given by Judd, <i>Volcanoes</i>, +p. 127.</p></div> +<p><span class="pagenum"><a name="Page_253" id="Page_253">[Pg 253]</a></span></p> + + +<hr class="major" /> +<h2><a name="PART_VII_CHAPTER_III" id="PART_VII_CHAPTER_III"></a>CHAPTER III. +<br /><br /> +ARE WE LIVING IN AN EPOCH OF SPECIAL +VOLCANIC ACTIVITY?</h2> + + +<p>The question which we are about to discuss in the +concluding chapter of this volume is one to which we +ought to be able to offer a definite answer. This +can only be arrived at by a comparison of the violence +and extent of volcanic and seismic phenomena within +the period of history with those of pre-historic periods.</p> + +<p>At first sight we might be disposed to give to the +question an affirmative reply when we remember the +eruptions of the last few years, and add to these the +volcanic outbursts and earthquake shocks which +history records. The cases of the earthquake and +eruption in Japan of November, 1891, where in one +province alone two thousand people lost their lives +and many thousand houses were levelled<a name="FNanchor_1_204" id="FNanchor_1_204"></a><a href="#Footnote_1_204" class="fnanchor">[1]</a>; that of +Krakatoa, in 1883; of Vesuvius, in 1872; and many +others of recent date which might be named, added +to those which history records;—the recollection of +such cases might lead us to conclude that our epoch +is one in which the subterranean volcanic forces had +broken out with extraordinary energy over the earth's +<span class="pagenum"><a name="Page_254" id="Page_254">[Pg 254]</a></span>surface. Still, when we come to examine into the cases +of recorded eruptions—especially those of great violence—we +find that they are limited to very special districts; +and even if we extend our retrospect into the +later centuries of our era, we shall find that the exceptionally +great eruptions have been confined to certain +permanently volcanic regions, such as the chain of +the Andes, that of the Aleutian, Kurile, Japanese, and +Philippine and Sunda Islands, lying for the most part +along the remarkable volcanic girdle of the world to +which I have referred in a previous page. Add to +these the cases of Iceland and the volcanic islands of +the Pacific, and we have almost the whole of the very +active volcanoes of the world.</p> + +<p>Then for the purposes of our inquiry we have to +ascertain how these active vents of eruption compare, +as regards the magnitude of their operations, +with those of the pre-historic and later Tertiary +times. But before entering into this question it maybe +observed, in the first place, that a large number of +the vents of eruption, even along the chain of the +earth's volcanic girdle, are dormant or extinct. This +observation applies to many of the great cones and +domes of the Andes, including Chimborazo and other +colossal mountains in Ecuador, Columbia, Chili, Peru, +and Mexico. The region between the eastern Rocky +Mountains and the western coast of North America +was, as we have seen, one over which volcanic eruptions +took place on a vast scale in later Tertiary +times; but one in which only the after-effects of +volcanic action are at present in operation. We have +also seen that the chain of volcanoes of Japan and of +the Kurile Islands are only active to a slight extent +as compared with former times, and the same observation +<span class="pagenum"><a name="Page_255" id="Page_255">[Pg 255]</a></span>applies to those of New Zealand. Out of 130 +volcanoes in the Japanese islands, only 48 are now +believed to be active.</p> + +<p>Again, if we turn to other districts we have been +considering, we find that in the Indian Peninsula, in +Arabia, in Syria and the Holy Land, in Persia, in +Abyssinia and Asia Minor—regions where volcanic +operations were exhibited on a grand scale throughout +the Tertiary period, and in some cases almost +down into recent times—we are met by similar evidences +either of decaying volcanic energy, or of an +energy which, as far as surface phenomena are concerned, +is a thing of the past. Lastly, turning our +attention to the European area, notwithstanding the +still active condition of Etna, Vesuvius, and a few +adjoining islands, we see in all directions throughout +Southern Italy evidences of volcanic operations of a +past time,—such as extinct crater-cones, lakes occupying +the craters of former volcanoes, and extensive +deposits of tuff or streams of lava—all concurring in +giving evidence of a period now past, when vulcanicity +was widespread over regions where its presence is +now never felt except when some earthquake shock, +like that of the Riviera, brings home to our minds the +fact that the motive force is still beneath our feet, +though under restrained conditions as compared with +a former period.</p> + +<p>Similar conclusions are applicable with even greater +force to other parts of the European area. The region +of the Lower Rhine and Moselle, of Hungary and the +Carpathians, of Central France, of the North of Ireland +and the Inner Hebrides, all afford evidence of +volcanic operations at a former period on an extensive +scale; and the contrast between the present physically +<span class="pagenum"><a name="Page_256" id="Page_256">[Pg 256]</a></span>silent and peaceful condition of these regions, as +regards any outward manifestations of sub-terrestrial +forces, compared with those which were formerly +prevalent, cannot fail to impress our minds irresistibly +with the idea that volcanic energy has well-nigh exhausted +itself over these tracts of the earth's surface.</p> + +<p>From this general survey of the present condition +of the earth's surface, as regards the volcanic operations +going on over it, and a comparison with those +of a preceding period, we are driven to the conclusion +that, however violent and often disastrous are the +volcanic and seismic phenomena of the present day, +they are restricted to comparatively narrow limits; +and that even within these limits the volcanic forces +are less powerful than they were in pre-historic times.</p> + +<p>The middle part of the Tertiary period appears, +in fact, to have been one of extraordinary volcanic +activity, whether we regard the wide area over which +this activity manifested itself, or the results as shown +by the great amount of the erupted materials. Many +of the still active volcanic chains, or groups, probably +had their first beginnings at the period referred to; +but in the majority of cases the eruptive forces have +become dormant or extinct. With the exception of +the lavas of the Indian-Peninsular area, which appear, +at least partially, to belong to the close of the Cretaceous +epoch, the specially volcanic period may +be considered to extend from the beginning of the +Miocene down to the close of the Pliocene stage. +During the Eocene stage, volcanic energy appears to +have been to a great degree dormant; but plutonic +energy was gathering strength for the great effort of +the Miocene epoch, when the volcanic forces broke +out with extraordinary violence over Europe, the +<span class="pagenum"><a name="Page_257" id="Page_257">[Pg 257]</a></span>British Isles, and other regions, and continued to +develop throughout the succeeding Pliocene epoch, +until the whole globe was surrounded by a girdle of +fire.</p> + +<hr class="tb" /> + +<p>The reply, therefore, to the question with which we +set out is very plain; and is to the effect that the +present epoch is one of comparatively low volcanic +activity. The further question suggests itself, whether +the volcanic phenomena of the middle Tertiary period +bear any comparison with those of past geological +times. This, though a question of great interest, is one +which is far too large to be discussed here; and it is +doubtful if we have materials available upon which to +base a conclusion. But it may be stated with some +confidence, in general terms, that the history of the +earth appears to show that, throughout all geological +time, our world has been the theatre of intermittent +geological activity, periods of rest succeeding those of +action; and if we are to draw a conclusion regarding +the present and future, it would be that, owing to the +lower rate of secular cooling of the crust, volcanic +action ought to become less powerful as the world +grows older.</p> + +<div class="footnote"><p><a name="Footnote_1_204" id="Footnote_1_204"></a><a href="#FNanchor_1_204"><span class="label">[1]</span></a> Admirably illustrated in Prof. J. Milne's recently published work, +<i>The Great Earthquake of Japan, 1891</i>.</p></div> + +<p><span class="pagenum"><a name="Page_259" id="Page_259">[Pg 259]</a></span></p> + +<hr class="major" /> +<h2><a name="APPENDIX" id="APPENDIX"></a>APPENDIX. +<br /><br /> +A BRIEF ACCOUNT OF THE PRINCIPAL VARIETIES +OF VOLCANIC ROCKS.</h2> + + +<p>The text-books on this subject are so numerous and accessible, +that a very brief account of the volcanic rocks is all that need +be given here for the purposes of reference by readers not +familiar with petrological details.</p> + +<p>Let it be observed, in the first place, that there is no hard and +fast line between the varieties of igneous and volcanic rocks. +In this as in other parts of creation—<i>natura nil facit per +saltum</i>; there are gradations from one variety to the other. +At the same time a systematic arrangement is not only desirable, +but necessary; and the most important basis of arrangement +is that founded on the proportion of <i>silica</i> (or quartz) in +the various rocks, as first demonstrated by Durocher and +Bunsen, who showed that silica plays the same part in the +inorganic kingdom that carbon does in the organic. Upon this +hypothesis, which is a very useful one to work with, these +authors separated all igneous and volcanic rocks into two +classes, viz., the Basic and the Acid; the former containing +from 45-58 per cent., the latter 62-78 per cent. of that mineral. +But there are a few intermediate varieties which serve to bridge +over the space between the Basic and Acid Groups. The following +is a generalised arrangement of the most important rocks +under the above heads:—</p> + +<p class="center"><i>Tabular View of Chief Igneous and Volcanic Rocks.</i></p> + +<div class="center"> +<table border="0" cellpadding="0" cellspacing="0" summary=""> +<tr><td align="center"> +<span class="smcap">Basic Group.</span></td></tr> +<tr><td align="left"> + 1. Basalt and Dolerite.</td></tr> +<tr><td align="left"> + 2. Gabbro.</td></tr> +<tr><td align="left"> +<span class="pagenum"><a name="Page_260" id="Page_260">[Pg 260]</a></span> 3. Diorite.</td></tr> +<tr><td align="left"> + 4. Diabase and Melaphyre.</td></tr> +<tr><td align="left"> + 5. Porphyrite.</td></tr> +<tr><td align="center" style="height:2em;"> +<span class="smcap">Intermediate Group.</span></td></tr> +<tr><td align="left"> + 6. Syenite.</td></tr> +<tr><td align="left"> + 7. Mica-trap, or Lampophyre.</td></tr> +<tr><td align="left"> + 8. Andesite.</td></tr> +<tr><td align="center" style="height:2em;"> +<span class="smcap">Acid Group.</span></td></tr> +<tr><td align="left"> + 9. Trachyte, Domite, and Phonolite.</td></tr> +<tr><td align="left"> +10. Rhyolite and Obsidian.</td></tr> +<tr><td align="left"> +11. Granophyre.</td></tr> +<tr><td align="left"> +12. Granite.</td></tr> +</table> +</div> + +<p>In the above grouping, and in the following definitions, I have +not been able to follow any special authority. But the most serviceable +text-books are those of Mr. Frank Rutley, <i>Study of +Rocks</i>, and Dr. Hatch, <i>Petrology</i>; also H. Rosenbusch, <i>Mikroskopische +Physiographie der Mineralien</i>, and F. Zirkel's <i>Untersuchungen +über mikroskopische Structur der Basaltgesteine</i>. We +shall consider these in the order above indicated:—</p> + +<p>1. <span class="smcap">Basalt.</span>—The most extensively distributed of all volcanic +rocks. It is a dense, dark rock of high specific gravity (2.4-2.8), +consisting of plagioclase felspar (Labradorite or anorthite), +augite, and titano-ferrite (titaniferous magnetite). Olivine is +often present; and when abundant the rock is called "olivine-basalt." +In the older rocks, basalt has often undergone decomposition +into melaphyre; and amongst the metamorphic rocks +it has been changed into diorite or hornblende rock; the augite +having been converted into hornblende.</p> + +<p>When leucite or nepheline replaces plagioclase, the rock +becomes a leucite-basalt,<a name="FNanchor_1_205" id="FNanchor_1_205"></a><a href="#Footnote_1_205" class="fnanchor">[1]</a> or nepheline-basalt. Some basalts +have a glass paste, or "ground-mass," in which the minerals +are enclosed.</p> + +<p>The lava of Vesuvius may be regarded as a variety of basalt +in which leucite replaces plagioclase, although this latter mineral +<span class="pagenum"><a name="Page_261" id="Page_261">[Pg 261]</a></span>is also present. Zirkel calls it "Sanidin-leucitgestein," as both +the macroscopic and microscopic structure reveal the presence +of leucite, sanidine, plagioclase, nephiline, augite, mica, olivine, +apatite, and magnetite.<a name="FNanchor_2_206" id="FNanchor_2_206"></a><a href="#Footnote_2_206" class="fnanchor">[2]</a></p> + +<p><i>Dolerite</i> does not differ essentially from basalt in composition +or structure, but is a largely crystalline-granular variety, +occurring more abundantly than basalt amongst the more +ancient rocks, and the different minerals are distinctly visible +to the naked eye.</p> + +<p>A remarkable variety of this rock occurs at Slieve Gullion in +Ireland, in which mica is so abundant as to constitute the rock +a "micaceous dolerite."</p> + +<p>2. <span class="smcap">Gabbro.</span>—A rather wide group of volcanic rocks with +variable composition. Essentially it is a crystalline-granular +compound of plagioclase, generally Labradorite and diallage. +Sometimes the pyroxenic mineral becomes hypersthene, giving +rise to <i>hypersthene-gabbro</i>; or when hornblende is present, to +<i>hornblende-gabbro</i>; when olivine, to <i>olivine-gabbro</i>. Magnetite +is always present.</p> + +<p>These rocks occur in the Carlingford district in Ireland, in +the Lizard district of Cornwall, the Inner Hebrides (Mull, +Skye, etc.) of Scotland, and in Saxony.</p> + +<p>3. <span class="smcap">Diorite.</span>—A crystalline-granular compound of plagioclase +and hornblende with magnetite. When quartz is present it +becomes (according to the usual British acceptation) a <i>syenite</i>; +but this view is gradually giving place to the German definition +of syenite, which is a compound of orthoclase and hornblende; +and it may be better to denominate the variety as <i>quartz-diorite</i>. +The diorites are abundant as sheets and dykes amongst +the older palæozoic and metamorphic rocks, and are sometimes +exceedingly rich in magnetite. Mica, epidote, and chlorite are +also present as accessories.</p> + +<p>The rock occurs in North Wales, Charnwood Forest, Wicklow, +Galway, and Donegal, and the Highlands of Scotland. +There can be little doubt that amongst the metamorphic rocks +of Galway, Mayo, and Donegal the great beds of (often columnar) +diorite were originally augitic lavas, which have since undergone +transformation.</p> + +<p><span class="pagenum"><a name="Page_262" id="Page_262">[Pg 262]</a></span></p><p>4. <span class="smcap">Diabase.</span>—It is very doubtful if "Diabase" ought to be +regarded as a distinct species of igneous rock, as it seems to be +simply an altered variety of basalt or dolerite, in which chlorite, +a secondary alteration-product, has been developed by the decomposition +of the pyroxene or olivine of the original rock. It +is a convenient name for use in the field when doubt occurs as +to the real nature of an igneous rock. Melaphyre is a name +given to the very dark varieties of altered augitic lavas, rich in +magnetite and chlorite.</p> + +<p>5. <span class="smcap">Porphyrite</span> (or quartzless porphyry).—A basic variety of +felstone-porphyry, consisting of a felspathic base with distinct +crystals of felspar, with which there may be others of hornblende, +mica, or augite. The colour is generally red or purple, +and it weathers into red clay, in contrast to the highly acid or +silicated felsites which weather into whitish sand.</p> + +<p>6. <span class="smcap">Syenite.</span>—As stated above, this name has been variously +applied. Its derivation is from Syene (Assouan) in Egypt, and +the granitic rocks of that district were called "syenites," under +the supposition (now known to be erroneous) that they differ from +ordinary granites in that they were supposed to be composed of +quartz, felspar, and hornblende, instead of quartz, felspar, and +mica. From this it arose that syenite was regarded as a variety of +granite in which the mica is replaced by hornblende, and this +has generally been the British view of the question. But the +German definition is applied to an entirely different rock, +belonging to the felstone family; and according to this classification +syenite consists of a crystalline-granular compound of +orthoclase and hornblende, in which quartz may or may not be +present. From this it will be seen that, according to Zirkel, +syenite is essentially distinct from diorite in the species of its +felspar.<a name="FNanchor_3_207" id="FNanchor_3_207"></a><a href="#Footnote_3_207" class="fnanchor">[3]</a> It seems desirable to adopt the German view; and as +regards diorites containing quartz as an accessory, to apply to +them the name of <i>quartz-diorite</i>, as stated above, the name +syenite as used by British geologists having arisen from a +misconception.</p> + +<p>7. <span class="smcap">Mica-trap (Lampophyre).</span>—A rock, allied to the felstone +family, in which mica is an abundant and essential constituent, +thus consisting of plagioclase and mica, with a little magnetite. +Quartz may be an accessory. This rock occurs amongst the +<span class="pagenum"><a name="Page_263" id="Page_263">[Pg 263]</a></span>Lower Silurian strata of Ireland, Cumberland, and the South of +Scotland; it is not volcanic in the ordinary acceptation of that +term. The term <i>lampophyre</i> was introduced by Gümbel in +describing the mica-traps of Fichtelgebirge.</p> + +<p>8. <span class="smcap">Andesite.</span>—This is a dark-coloured, compact or vesicular, +semi-vitreous group of volcanic rocks, composed essentially +of a glassy plagioclase felspar, and a ferro-magnesian +constituent enclosed in a glassy base. According to the nature +of the ferro-magnesian constituent, the group may be divided into +<i>hornblende-andesite</i>, <i>biotite-andesite</i>, and <i>augite-andesite</i>. Quartz +is sometimes present, and when this mineral becomes an essential +it gives rise to a variety called <i>quartz-andesite</i> or <i>dacite</i>.</p> + +<p>These rocks are the principal constituents of the lavas of the +Andes, and the name was first applied to them by Leopold von +Buch; but their representatives also occur in the British Isles, +Germany, and elsewhere. Dacite is the lava of Krakatoa and +some of the volcanoes of Japan.</p> + +<p>9, 10. <span class="smcap">Trachyte</span> and <span class="smcap">Domite</span>, etc.—These names include very +numerous varieties of highly silicated volcanic rock, and in their +general form consist of a white felsitic paste with distinct +crystals of sanidine, together with plagioclase, augite, biotite, +hornblende, and accessories. When crystalline grains or blebs +of quartz occur, we have a quartz-trachyte; when tridymite is +abundant, as in the trachyte of Co. Antrim, we have "tridymite-trachyte."</p> + +<p>The trachytes occupy a position between the pitchstone lavas +on the one hand, and the andesites and granophyres on the +other.</p> + +<p>(<i>b.</i>) <i>Domite</i> is the name applied to the trachytic rocks of the +Auvergne district and the Puy de Dôme particularly. They do +not contain free quartz, though they are highly acid rocks, containing +sometimes as much as 68 per cent. of silica.</p> + +<p>(<i>c.</i>) <i>Phonolite (Clinkstone)</i> is a trachytic rock, composed +essentially of sanidine, nepheline, and augite or hornblende. +It is usually of a greenish colour, hard and compact, so as +to ring under the hammer; hence the name. The Wolf Rock +is composed of phonolite, and it occurs largely in Auvergne.</p> + +<p>(<i>d.</i>) <i>Rhyolites</i> are closely connected with the <i>quartz-trachytes</i>, +but present a marked fluidal, spherulitic, or perlitic structure. +They consist of a trachytic ground-mass in which grains or +<span class="pagenum"><a name="Page_264" id="Page_264">[Pg 264]</a></span>crystals of quartz and sanidine, with other accessory minerals, +are imbedded. They occur amongst the volcanic rocks of the +British Isles, Hungary, and the Lipari Islands, from which the +name <i>Liparite</i> has been derived.</p> + +<p>(<i>e.</i>) <i>Obsidian (Pitchstone).</i>—This is a vitreous, highly acid +rock, which has become a volcanic glass in consequence of +rapid cooling, distinct minerals not having had time to +form. It has a conchoidal fracture, various shades of colour +from grey to black; and under the microscope is seen to contain +crystallites or microliths, often beautifully arranged in stellate or +feathery groups. Spherulitic structure is not infrequent; and +occasionally a few crystals of sanidine, augite, or hornblende +are to be seen imbedded in the glassy ground-mass. The rock +occurs in dykes and veins in the Western Isles of Scotland, in +Antrim, and on the borders of the Mourne Mountains, near +Newry, in Ireland.</p> + +<p>11. <span class="smcap">Granophyre.</span>—This term, according to Geikie, embraces +the greater portion of the acid volcanic rocks of the +Inner Hebrides. They are closely allied to the quartz-porphyries, +and vary in texture from a fine felsitic or crystalline-granular +quartz-porphyry, in the ground-mass of which +porphyritic turbid felspar and quartz may generally be detected, +to a granitoid rock of medium grain, in which the +component dull felspar and clear quartz can be readily distinguished +by the naked eye. Throughout all the varieties of +texture there is a strong tendency to the development of +minute irregularly-shaped cavities, inside of which quartz or +felspar has crystallised out—a feature characteristic of the +granites of Arran and of the Mourne Mountains.</p> + +<p>12. <span class="smcap">Granite.</span>—A true granite consists of a crystalline-granular +rock consisting of quartz, felspar (orthoclase), and +mica; the quartz is the paste or ground-mass in which the +felspar and mica crystals are enclosed. This is the essential +distinction between a granite and a quartz-porphyry or a granophyre. +Owing to the presence of highly-heated steam under +pressure in the body of the mass when in a molten condition, +the quartz has been the last of the minerals to crystallise out, +and hence does not itself occur with the crystalline form.</p> + +<p>True granite is not a volcanic rock, and its representatives +amongst volcanic ejecta are to be found in the granophyres, +<span class="pagenum"><a name="Page_265" id="Page_265">[Pg 265]</a></span>quartz-porphyries, felsites, trachytes, and rhyolites so abundant +in most volcanic countries, and to one or other of these the +so-called granites of the Mourne Mountains, of Arran Island, +and of Skye are to be referred. Granite is a rock which has +been intruded in a molten condition amongst the deep-seated +parts of the crust, and has consolidated under great pressure in +presence of aqueous vapour and with extreme slowness, resulting +in the formation of a rock which is largely crystalline-granular. +Its presence at the surface is due to denudation of the masses +by which it was originally overspread.</p> + +<div class="figcenter"> +<a name="PLATE_1"> + <span class="center"><span class="smcap">Plate I.</span></span><br /> + <img src="images/plate1.jpg" alt="Plate I" /> +</a> +</div> + +<h2>EXPLANATION OF PLATE I.</h2> + +<p class="center">MAGNIFIED SECTIONS OF VESUVIAN MINERALS.</p> + +<blockquote><p>Fig. 1. Section of leucite crystal from the lava of 1868, with fluid +cavities. Mag., 350 diams.</p> + +<p>" 2, 3, 4, and 5. Sections of nepheline crystals from the lava of +1767, 1834, and 1854.</p> + +<p>" 6. Section of sodalite crystal from the lava of 1794, with belonites +and crystals of magnetite enclosed.</p> + +<p>" 7, 8, 9. Crystals of leucite with microliths and cavities darkened +by magnetite dust; also, containing crystals of magnetite.</p> + +<p>" 10. Group of leucite crystals of irregular form from the lava of +1855, congregated around a nucleus of crystals of plagioclase +and magnetite.</p></blockquote> + +<div class="figcenter"> +<a name="PLATE_2"> + <span class="center"><span class="smcap">Plate II.</span></span><br /> + <img src="images/plate2.jpg" alt="Plate II" /> +</a> +</div> + +<h2>EXPLANATION OF PLATE II.</h2> + +<p class="center">MAGNIFIED SECTIONS OF VESUVIAN MINERALS.</p> + +<blockquote><p>Fig. 1. Section of augite crystal from the lava of 1794, with numerous +gas cells and delicately banded walls. The interior contains +two long prisms, probably of apatite.</p> + +<p>" 2. Crystal of augite with banded walls, and indented by leucite +crystals, from the lava of 1794. Mag., 40 diams.</p> + +<p>" 3, 4, 5. Sections of augite crystals from the lavas of 1794 and +1820.</p> + +<p>" 6. Group of augite crystals from the lava of 1835.</p> + +<p>" 7. Ditto from the lava of 1822, with encluded mica-flake (<i>a</i>) and +portion of the glass paste, or ground-mass, of the rock (<i>b</i>), +containing microliths and grains of magnetite.</p> + +<p><span class="pagenum"><a name="Page_266" id="Page_266">[Pg 266]</a></span></p><p>Fig. 8. Two crystals of olivine from the lava of 1855; they are intersected +on one side by the plane of the thin section, and are +remarkable for showing lines of gas cells, and bands of growth +sometimes cellular. Mag., 40 diams.</p> + +<p>" 9. Section of rock-crystal (quartz), with double terminal pyramids, +from the lava of 1850.</p> + +<p>" 10. Twin crystal of sanidine from the lava of 1858. Mag., 40 +diams.</p> + +<p>" 11, 12, 13. Sections of plagioclase crystals (probably labradorite) +from the lava of 1855. Mag., 100 diams.</p> + +<p>" 14. Section of olivine crystal from the lava of 1631—imperfectly +formed. Mag., 30 diams.</p> + +<p>" 15. Section of mica-flake from the lava of 1822. Mag., 30 diams.</p></blockquote> + +<div class="figcenter"> +<a name="PLATE_3"> + <span class="center"><span class="smcap">Plate III.</span></span><br /> + <img src="images/plate3.jpg" alt="Plate III" /> +</a> +</div> + +<h2>EXPLANATION OF PLATE III.</h2> + +<p class="center">MAGNIFIED SECTIONS OF VOLCANIC ROCKS.</p> + +<blockquote><p>1. Diorite dyke, traversing Assynt limestone, North Highlands.</p> + +<p>2. Basalt from upper beds, near Giant's Causeway, County Antrim.</p> + +<p>3. Hornblende-hypersthene-augite Andesite, from Pichupichu, Andes.</p> + +<p>4. Augite-Andesite from Pichupichu, Andes.</p> + +<p>5. Olivine dolerite, with hornblende and biotite, Madagascar.</p> + +<p>6. Leucite basalt, with mellilite, Capo di Bove, Italy.</p></blockquote> + +<div class="figcenter"> +<a name="PLATE_4"> + <span class="center"><span class="smcap">Plate IV.</span></span><br /> + <img src="images/plate4.jpg" alt="Plate IV" /> +</a> +</div> + +<h2>EXPLANATION OF PLATE IV.</h2> + +<p class="center">MAGNIFIED SECTIONS OF VOLCANIC ROCKS.</p> + +<blockquote><p>1. Vesuvian lava, glass paste with numerous crystals of leucite; others +of augite and nepheline porphyritically developed; also small +grains of magnetite.</p> + +<p>2. Vesuvian lava, glass paste with numerous crystals of leucite; others +of olivine, hornblende, and sanidine, porphyritically developed; +small grains of magnetite.</p> + +<p>3. Trachyte from Hungary; felsitic paste with crystals of hornblende +and sanidine, and a little magnetite.</p> + +<p>4. Gabbro, from Carlingford Hill, Ireland, consisting of anorthite, +augite, a little olivine, and magnetite.</p> + +<p>5. Dolerite, from old volcanic neck, Scalot Hill, near Lame, consisting +of labradorite, augite, olivine, and magnetite.</p> + +<p>6. Dolerite, Ballintoy, County Antrim, showing ophetic structure, +consisting of augite, labradorite, and magnetite.</p></blockquote> + +<div class="footnote"><p><a name="Footnote_1_205" id="Footnote_1_205"></a><a href="#FNanchor_1_205"><span class="label">[1]</span></a> Mr. S. Allport has discovered this in the rock called the "Wolf +Rock" off the coast of Cornwall. The most important work on basalt +is that by F. Zirkel, <i>Unters. über mikros. Zusammensetzung und Structur +der Basaltgesteine</i>. Bonn (1870).</p></div> + +<div class="footnote"><p><a name="Footnote_2_206" id="Footnote_2_206"></a><a href="#FNanchor_2_206"><span class="label">[2]</span></a> Zirkel, <i>Die mikroskopische Beschaffenheit der Mineralien und Gesteine</i>, +p. 153. Leipsig (1873).</p></div> + +<div class="footnote"><p><a name="Footnote_3_207" id="Footnote_3_207"></a><a href="#FNanchor_3_207"><span class="label">[3]</span></a> Zirkel, <i>Petrog.</i>, i. 578; B. von Cotta, p. 178 (Eng. Trans.).</p></div> +<p><span class="pagenum"><a name="Page_267" id="Page_267">[Pg 267]</a></span></p> + + +<hr class="major" /> +<h1>INDEX.</h1> +<p><span class="pagenum"><a name="Page_268" id="Page_268">[Pg 268]</a></span></p> + + +<hr class="major" /> +<h2><a name="INDEX" id="INDEX"></a>INDEX.</h2> + + +<p> +Abyssinian table-lands, <a href="#Page_190">190</a> <i>et seq.</i><br /> +<br /> +Albano, Lake, <a href="#Page_89">89</a><br /> +<br /> +America, volcanic regions of North, <a href="#Page_136">136</a> <i>et seq.</i>;<br /> +<span style="margin-left: 1em;">of Western, <a href="#Page_144">144</a></span><br /> +<br /> +Andes, <a href="#Page_18">18</a>, <a href="#Page_27">27</a>, <a href="#Page_227">227</a>, <a href="#Page_254">254</a><br /> +<br /> +Andesite, <a href="#Page_263">263</a><br /> +<br /> +Antrim, <a href="#Page_154">154</a> <i>et seq.</i><br /> +<br /> +Arabia, dormant volcanoes of, <a href="#Page_126">126</a>-<a href="#Page_135">135</a><br /> +<br /> +Arabian desert, <a href="#Page_134">134</a><br /> +<br /> +Archibald, C. D., <a href="#Page_213">213</a><br /> +<br /> +Arizona, volcanoes of, <a href="#Page_137">137</a><br /> +<br /> +Argyll, Duke of, <a href="#Page_173">173</a><br /> +<br /> +Ascension, <a href="#Page_36">36</a><br /> +<br /> +Ashangi, volcanic series of, <a href="#Page_192">192</a><br /> +<br /> +Atmospheric effects of Krakatoa eruption, <a href="#Page_213">213</a>-<a href="#Page_214">214</a><br /> +<br /> +Auckland district, volcanoes of, <a href="#Page_147">147</a><br /> +<br /> +Auvergne, volcanic regions of, <a href="#Page_14">14</a>, <a href="#Page_16">16</a>, <a href="#Page_92">92</a> <i>et seq.</i><br /> +<br /> +Azores, <a href="#Page_32">32</a><br /> +<br /> +<br /> +Ball, Sir R. S., <a href="#Page_242">242</a>, <a href="#Page_244">244</a><br /> +<br /> +Basalt, <a href="#Page_260">260</a><br /> +<br /> +Blanford, W. T., <a href="#Page_188">188</a>, <a href="#Page_189">189</a><br /> +<br /> +Bonneville, Lake, <a href="#Page_141">141</a>-<a href="#Page_142">142</a><br /> +<br /> +British Isles,<br /> +<span style="margin-left: 1em;">Tertiary volcanic districts of, <a href="#Page_154">154</a> <i>et seq.</i>, <a href="#Page_227">227</a>;</span><br /> +<span style="margin-left: 1em;">pre-Tertiary volcanic districts of, <a href="#Page_196">196</a> <i>et seq.</i></span><br /> +<br /> +Buch, L. von, <a href="#Page_6">6</a>, <a href="#Page_11">11</a>, <a href="#Page_24">24</a><br /> +<br /> +<br /> +California, volcanoes of, <a href="#Page_140">140</a><br /> +<br /> +Callirrhoë, springs of, <a href="#Page_133">133</a><br /> +<br /> +Cañon, the Grand, <a href="#Page_138">138</a><br /> +<br /> +Cantal, volcanoes of the, <a href="#Page_99">99</a>-<a href="#Page_101">101</a><br /> +<br /> +Cape Colony, Basalts of, <a href="#Page_194">194</a><br /> +<br /> +Charleston earthquake, <a href="#Page_218">218</a>, <a href="#Page_222">222</a>, <a href="#Page_224">224</a><br /> +<br /> +Chambers, G. F., <a href="#Page_246">246</a><br /> +<br /> +Charnwood Forest, <a href="#Page_198">198</a><br /> +<br /> +Chimborazo, <a href="#Page_18">18</a><br /> +<br /> +Clermont, vale of, <a href="#Page_96">96</a>-<a href="#Page_97">97</a><br /> +<br /> +Clinkstone, <a href="#Page_263">263</a><br /> +<br /> +Cordilleras of Quito, <a href="#Page_25">25</a><br /> +<br /> +Cotopaxi, <a href="#Page_16">16</a>-<a href="#Page_18">18</a>, <a href="#Page_24">24</a>, <a href="#Page_26">26</a><br /> +<br /> +Crater-cones, Lava, <a href="#Page_19">19</a><br /> +<br /> +Crateriform cones, <a href="#Page_13">13</a><br /> +<br /> +Craterless domes, <a href="#Page_15">15</a><br /> +<br /> +<br /> +Dana, Prof. J. D., <a href="#Page_19">19</a>, <a href="#Page_39">39</a>, <a href="#Page_249">249</a><br /> +<br /> +Darwin, <a href="#Page_28">28</a>, <a href="#Page_30">30</a><br /> +<br /> +Darwin, Prof. G. H., <a href="#Page_9">9</a>, <a href="#Page_231">231</a><br /> +<br /> +Daubeny, <a href="#Page_7">7</a>, <a href="#Page_61">61</a>, <a href="#Page_69">69</a><br /> +<br /> +Davison, C., <a href="#Page_9">9</a>, <a href="#Page_231">231</a><br /> +<br /> +Davy, Sir H., <a href="#Page_11">11</a><br /> +<br /> +Deccan trap-series, <a href="#Page_187">187</a> <i>et seq.</i><br /> +<br /> +Demavend, Mount, <a href="#Page_24">24</a><br /> +<br /> +Diabase, <a href="#Page_262">262</a><br /> +<br /> +Diorite, <a href="#Page_261">261</a><br /> +<br /> +Dolerite, <a href="#Page_261">261</a><br /> +<br /> +Domite, <a href="#Page_263">263</a><br /> +<br /> +Dore, volcanoes of Mont, <a href="#Page_100">100</a>-<a href="#Page_101">101</a><br /> +<br /> +Doughty, C. M., <a href="#Page_127">127</a><br /> +<br /> +Durocher, <a href="#Page_232">232</a><br /> +<br /> +Dutton, Capt. C. E., <a href="#Page_9">9</a>, <a href="#Page_220">220</a>, <a href="#Page_222">222</a><br /> +<br /> +Dykes in Ireland, <a href="#Page_169">169</a>-<a href="#Page_170">170</a><br /> +<br /> +<br /> +Earthquakes, <a href="#Page_217">217</a> <i>et seq.</i><br /> +<br /> +Errigal, <a href="#Page_10">10</a><br /> +<br /> +<span class="pagenum"><a name="Page_269" id="Page_269">[Pg 269]</a></span>Etna, <a href="#Page_14">14</a>, <a href="#Page_61">61</a> <i>et seq.</i>, <a href="#Page_229">229</a><br /> +<br /> +<br /> +Fingal's Cave, <a href="#Page_185">185</a><br /> +<br /> +Forbes, D., <a href="#Page_27">27</a><br /> +<br /> +France, extinct volcanoes of, <a href="#Page_92">92</a> <i>et seq.</i><br /> +<br /> +<br /> +Gabbro, <a href="#Page_261">261</a><br /> +<br /> +Gardner, J. S., <a href="#Page_156">156</a><br /> +<br /> +Geikie, Sir A., <a href="#Page_8">8</a>, <a href="#Page_29">29</a>, <a href="#Page_143">143</a>, <a href="#Page_156">156</a>, <a href="#Page_160">160</a>, <a href="#Page_169">169</a>, <a href="#Page_172">172</a>, <a href="#Page_176">176</a>, <a href="#Page_177">177</a>, <a href="#Page_196">196</a><br /> +<br /> +Giant's Causeway, <a href="#Page_165">165</a>-<a href="#Page_166">166</a><br /> +<br /> +Granite, <a href="#Page_264">264</a><br /> +<br /> +Granophyre, <a href="#Page_264">264</a>; of Mull, <a href="#Page_174">174</a><br /> +<br /> +Green, Prof. A. H., <a href="#Page_194">194</a><br /> +<br /> +<br /> +Hatch, Dr., <a href="#Page_260">260</a><br /> +<br /> +Haughton, Prof., <a href="#Page_68">68</a><br /> +<br /> +Haurân, volcanoes of the, <a href="#Page_22">22</a>, <a href="#Page_129">129</a><br /> +<br /> +Haute Loire, volcanic districts of, <a href="#Page_101">101</a>-<a href="#Page_105">105</a><br /> +<br /> +Hawaii, volcanoes of, <a href="#Page_39">39</a>, <a href="#Page_249">249</a>, <a href="#Page_251">251</a><br /> +<br /> +Hecla, <a href="#Page_32">32</a><br /> +<br /> +Herschel, Sir J., <a href="#Page_244">244</a><br /> +<br /> +Hibbert, Dr. S., <a href="#Page_6">6</a>, <a href="#Page_114">114</a>, <a href="#Page_124">124</a><br /> +<br /> +Hochstetter, F. von, <a href="#Page_147">147</a><br /> +<br /> +Hopkins, <a href="#Page_171">171</a>, <a href="#Page_217">217</a><br /> +<br /> +Hull, Dr. E. G., <a href="#Page_110">110</a><br /> +<br /> +Humboldt, A. von, <a href="#Page_20">20</a>, <a href="#Page_25">25</a><br /> +<br /> +Hutton, James, <a href="#Page_5">5</a><br /> +<br /> +<br /> +Iceland, volcanoes of, <a href="#Page_30">30</a>-<a href="#Page_32">32</a><br /> +<br /> +Ireland, volcanic Tertiary rocks of, <a href="#Page_154">154</a> <i>et seq.</i><br /> +<br /> +<br /> +Jaulân, <a href="#Page_129">129</a><br /> +<br /> +Johnston-Lavis, <a href="#Page_52">52</a><br /> +<br /> +Jordan valley, <a href="#Page_126">126</a> <i>et seq.</i>, <a href="#Page_226">226</a><br /> +<br /> +Jorullo, <a href="#Page_24">24</a><br /> +<br /> +Judd, Prof., <a href="#Page_8">8</a>, <a href="#Page_68">68</a>, <a href="#Page_69">69</a>, <a href="#Page_71">71</a>, <a href="#Page_172">172</a>, <a href="#Page_178">178</a>, <a href="#Page_208">208</a><br /> +<br /> +<br /> +Krakatoa, eruption of, <a href="#Page_206">206</a> <i>et seq.</i><br /> +<br /> +Kurile Islands, volcanoes of, <a href="#Page_28">28</a><br /> +<br /> +<br /> +Laacher See, <a href="#Page_121">121</a>-<a href="#Page_123">123</a><br /> +<br /> +Lampophyre, <a href="#Page_262">262</a><br /> +<br /> +Lancerote, <a href="#Page_34">34</a><br /> +<br /> +Lasaulx, Prof. von, <a href="#Page_68">68</a><br /> +<br /> +Lavas, relative density of, <a href="#Page_232">232</a>-<a href="#Page_234">234</a><br /> +<br /> +Lima in 1746, earthquake of, <a href="#Page_222">222</a><br /> +<br /> +Lipari Islands, volcanoes of, <a href="#Page_69">69</a> <i>et seq.</i><br /> +<br /> +Lisbon, earthquake of, <a href="#Page_221">221</a><br /> +<br /> +Lister, J. J., <a href="#Page_38">38</a><br /> +<br /> +Lunar volcanoes, <a href="#Page_236">236</a> <i>et seq.</i><br /> +<br /> +Lyell, Sir C., <a href="#Page_30">30</a>, <a href="#Page_62">62</a>, <a href="#Page_78">78</a>, <a href="#Page_217">217</a><br /> +<br /> +<br /> +Mackowen, Col., <a href="#Page_74">74</a><br /> +<br /> +Magdala, volcanic series of, <a href="#Page_192">192</a>-<a href="#Page_193">193</a><br /> +<br /> +Mallet, R., <a href="#Page_9">9</a>, <a href="#Page_217">217</a><br /> +<br /> +Mauna Loa, <a href="#Page_19">19</a>, <a href="#Page_39">39</a>, <a href="#Page_249">249</a><br /> +<br /> +Mica-trap, <a href="#Page_262">262</a><br /> +<br /> +Milne, Prof., <a href="#Page_28">28</a>, <a href="#Page_218">218</a>, <a href="#Page_253">253</a><br /> +<br /> +Moab, volcanic regions of, <a href="#Page_132">132</a><br /> +<br /> +Moon, volcanoes of, <a href="#Page_236">236</a> <i>et seq.</i><br /> +<br /> +Monte Nuovo, <a href="#Page_85">85</a><br /> +<br /> +Mull, <a href="#Page_172">172</a> <i>et seq.</i><br /> +<br /> +<br /> +Neapolitan group of volcanoes, <a href="#Page_28">28</a><br /> +<br /> +New Zealand, volcanoes of, <a href="#Page_146">146</a><br /> +<br /> +<br /> +Obsidian, <a href="#Page_264">264</a><br /> +<br /> +Ocean waves of seismic origin, <a href="#Page_208">208</a>, <a href="#Page_220">220</a><br /> +<br /> +O'Reilly, Prof., <a href="#Page_9">9</a>, <a href="#Page_219">219</a><br /> +<br /> +Orizaba, <a href="#Page_21">21</a><br /> +<br /> +Ovid, <a href="#Page_3">3</a><br /> +<br /> +<br /> +Pacific, volcanic islands of, <a href="#Page_37">37</a><br /> +<br /> +Palestine, dormant volcanoes of, <a href="#Page_126">126</a>-<a href="#Page_135">135</a><br /> +<br /> +Palmieri, Prof., <a href="#Page_55">55</a><br /> +<br /> +Pantelleria, <a href="#Page_74">74</a><br /> +<br /> +Phlegræan fields, <a href="#Page_85">85</a><br /> +<br /> +Phonolite, <a href="#Page_263">263</a><br /> +<br /> +Pitchstone, <a href="#Page_264">264</a><br /> +<br /> +Pliny, <a href="#Page_2">2</a>, <a href="#Page_4">4</a><br /> +<br /> +Porphyrite, <a href="#Page_262">262</a><br /> +<br /> +Powell, Major, <a href="#Page_138">138</a><br /> +<br /> +Pre-Tertiary volcanic rocks, <a href="#Page_187">187</a> <i>et seq.</i>;<br /> +<span style="margin-left: 1em;">of British Isles, <a href="#Page_196">196</a> <i>et seq.</i></span><br /> +<br /> +Puy de Dôme, <a href="#Page_105">105</a>-<a href="#Page_110">110</a><br /> +<br /> +Pythagoreans on volcanoes, <a href="#Page_2">2</a>-<a href="#Page_3">3</a><br /> +<br /> +<br /> +Quito, Cordilleras of, <a href="#Page_25">25</a><br /> +<br /> +<br /> +Rangitoto, <a href="#Page_19">19</a>, <a href="#Page_149">149</a><br /> +<br /> +Reyer, Dr. E., <a href="#Page_17">17</a><br /> +<br /> +Rhine valley, volcanoes of, <a href="#Page_113">113</a> <i>et seq.</i><br /> +<br /> +<span class="pagenum"><a name="Page_270" id="Page_270">[Pg 270]</a></span>Rhyolite, <a href="#Page_263">263</a><br /> +<br /> +Riviera in 1887, earthquake of, <a href="#Page_219">219</a><br /> +<br /> +Rocca Monfina, <a href="#Page_80">80</a><br /> +<br /> +Roderberg, <a href="#Page_119">119</a>, <a href="#Page_120">120</a><br /> +<br /> +Rome, <a href="#Page_88">88</a>-<a href="#Page_89">89</a><br /> +<br /> +Rosenbusch, H., <a href="#Page_260">260</a><br /> +<br /> +Roto Mahana, <a href="#Page_151">151</a><br /> +<br /> +Ruapahu, <a href="#Page_151">151</a><br /> +<br /> +Russell, Hon. Rollo, <a href="#Page_213">213</a><br /> +<br /> +Rutley, F., <a href="#Page_260">260</a><br /> +<br /> +<br /> +St. Helena, <a href="#Page_37">37</a><br /> +<br /> +San Francisco, Mount, <a href="#Page_138">138</a><br /> +<br /> +Santorin, <a href="#Page_76">76</a>-<a href="#Page_83">83</a><br /> +<br /> +Schehallion, <a href="#Page_10">10</a><br /> +<br /> +Schumacher, <a href="#Page_127">127</a><br /> +<br /> +Scotland, volcanic districts of, <a href="#Page_172">172</a> <i>et seq.</i><br /> +<br /> +Scrope, Poulett, <a href="#Page_5">5</a>, <a href="#Page_73">73</a>, <a href="#Page_93">93</a>, <a href="#Page_98">98</a><br /> +<br /> +Scuir of Eigg, <a href="#Page_180">180</a>-<a href="#Page_184">184</a><br /> +<br /> +Seismic phenomena, special, <a href="#Page_201">201</a> <i>et seq.</i>, <a href="#Page_217">217</a> <i>et seq.</i><br /> +<br /> +Shasta, Mount, <a href="#Page_140">140</a><br /> +<br /> +Siebengebirge, <a href="#Page_116">116</a>-<a href="#Page_120">120</a><br /> +<br /> +Skye, <a href="#Page_177">177</a>-<a href="#Page_179">179</a><br /> +<br /> +Sleamish, <a href="#Page_168">168</a><br /> +<br /> +Smyth, Piazzi, <a href="#Page_33">33</a><br /> +<br /> +Snake River, volcanoes of, <a href="#Page_142">142</a><br /> +<br /> +Staffa, <a href="#Page_185">185</a>-<a href="#Page_186">186</a><br /> +<br /> +Strabo on volcanoes, <a href="#Page_3">3</a><br /> +<br /> +Stromboli, <a href="#Page_71">71</a>-<a href="#Page_73">73</a><br /> +<br /> +Sumatra, volcanic action in, <a href="#Page_226">226</a><br /> +<br /> +Syenite, <a href="#Page_262">262</a><br /> +<br /> +Symes, R. G., <a href="#Page_167">167</a><br /> +<br /> +Syria, earthquakes in, <a href="#Page_219">219</a><br /> +<br /> +<br /> +Taupo Lake, <a href="#Page_150">150</a><br /> +<br /> +Taylor, Mount, <a href="#Page_138">138</a><br /> +<br /> +Tell el Ahmâr, <a href="#Page_131">131</a><br /> +<br /> +Tell el Akkasheh, <a href="#Page_131">131</a><br /> +<br /> +Tell el Farras, <a href="#Page_131">131</a><br /> +<br /> +Tell Abû en Nedâ, <a href="#Page_130">130</a><br /> +<br /> +Tell Abû Nedîr, <a href="#Page_129">129</a><br /> +<br /> +Templepatrick, quarry at, <a href="#Page_160">160</a><br /> +<br /> +Teneriffe, <a href="#Page_33">33</a><br /> +<br /> +Tertiary period, volcanic activity of, <a href="#Page_255">255</a><br /> +<br /> +Thucydides, <a href="#Page_2">2</a><br /> +<br /> +Tonga Islands, volcanoes of, <a href="#Page_38">38</a><br /> +<br /> +Tongariro, <a href="#Page_151">151</a><br /> +<br /> +Trachyte, <a href="#Page_263">263</a><br /> +<br /> +Trass of Brühl Valley, <a href="#Page_123">123</a>-<a href="#Page_125">125</a><br /> +<br /> +Tristan da Cunha, <a href="#Page_37">37</a><br /> +<br /> +Tristram, Canon, <a href="#Page_127">127</a>, <a href="#Page_131">131</a><br /> +<br /> +<br /> +Utah, volcanoes of, <a href="#Page_137">137</a><br /> +<br /> +<br /> +Verbeek, R. D. M., <a href="#Page_202">202</a><br /> +<br /> +Vesuvius, <a href="#Page_4">4</a>, <a href="#Page_14">14</a>, <a href="#Page_41">41</a>-<a href="#Page_60">60</a>, <a href="#Page_67">67</a>, <a href="#Page_229">229</a><br /> +<br /> +Volcanoes,<br /> +<span style="margin-left: 1em;">historic notices of, <a href="#Page_1">1</a>-<a href="#Page_5">5</a>;</span><br /> +<span style="margin-left: 1em;">form, structure, and composition of, <a href="#Page_10">10</a>-<a href="#Page_19">19</a>;</span><br /> +<span style="margin-left: 1em;">lines and groups of active, <a href="#Page_20">20</a>-<a href="#Page_29">29</a>;</span><br /> +<span style="margin-left: 1em;">of mid-ocean, <a href="#Page_30">30</a>-<a href="#Page_40">40</a>;</span><br /> +<span style="margin-left: 1em;">extinct or dormant, <a href="#Page_84">84</a> <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">special volcanic and seismic phenomena, <a href="#Page_201">201</a> <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">the ultimate cause of volcanic action, <a href="#Page_225">225</a> <i>et seq.</i>;</span><br /> +<span style="margin-left: 1em;">whether we are living in an epoch of special volcanic activity, <a href="#Page_253">253</a>-<a href="#Page_256">256</a>;</span><br /> +<span style="margin-left: 1em;">brief account of volcanic rocks, <a href="#Page_259">259</a>-<a href="#Page_265">265</a></span><br /> +<br /> +Vulcanists, <a href="#Page_5">5</a><br /> +<br /> +Vulcano, <a href="#Page_69">69</a>, <a href="#Page_71">71</a><br /> +<br /> +<br /> +Wallace, A. R., <a href="#Page_81">81</a><br /> +<br /> +Waltershausen, W. S. von, <a href="#Page_7">7</a>, <a href="#Page_61">61</a><br /> +<br /> +Wellington, Mount, <a href="#Page_149">149</a><br /> +<br /> +Wharton, Capt., <a href="#Page_212">212</a><br /> +<br /> +Whymper, E., <a href="#Page_18">18</a><br /> +<br /> +<br /> +Yarmûk, valley of the, <a href="#Page_129">129</a>, <a href="#Page_131">131</a><br /> +<br /> +Yellowstone Park, <a href="#Page_145">145</a><br /> +<br /> +<br /> +Zirkel, F., <a href="#Page_260">260</a><br /> +<br /> +Zöllner, <a href="#Page_240">240</a><br /> +</p> + + +<p class="center">THE WALTER SCOTT PRESS, NEWCASTLE-ON-TYNE.</p> + + + +<hr class="major" /> +<h2><a name="The_Contemporary_Science_Series" id="The_Contemporary_Science_Series"></a>The Contemporary Science Series.</h2> + +<p class="center">EDITED BY HAVELOCK ELLIS.</p> + +<hr class="tb" /> + +<p class="center">Crown 8vo, Cloth, 3s. 6d. per vol.; Half Morocco, 6s. 6d.</p> + +<blockquote><p>I. THE EVOLUTION OF SEX. By Professor <span class="smcap">Patrick Geddes</span> and +<span class="smcap">J. Arthur Thomson</span>. With 90 Illustrations. Second Edition.</p></blockquote> + +<p>"The authors have brought to the task—as indeed their names guarantee—a +wealth of knowledge, a lucid and attractive method of treatment, and a +rich vein of picturesque language."—<i>Nature.</i></p> + +<blockquote><p>II. ELECTRICITY IN MODERN LIFE. By <span class="smcap">G. W. de Tunzelmann</span>. +With 88 Illustrations.</p></blockquote> + +<p>"A clearly-written and connected sketch of what is known about electricity +and magnetism, the more prominent modern applications, and the principles +on which they are based."—<i>Saturday Review.</i></p> + +<blockquote><p>III. THE ORIGIN OF THE ARYANS. By Dr. <span class="smcap">Isaac Taylor</span>. Illustrated. +Second Edition.</p></blockquote> + +<p>"Canon Taylor is probably the most encyclopædic all-round scholar now +living. His new volume on the Origin of the Aryans is a first-rate example of +the excellent account to which he can turn his exceptionally wide and varied +information.... Masterly and exhaustive."—<i>Pall Mall Gazette.</i></p> + +<blockquote><p>IV. PHYSIOGNOMY AND EXPRESSION. By <span class="smcap">P. Mantegazza</span>. +Illustrated.</p></blockquote> + +<p>"Professor Mantegazza is a writer full of life and spirit, and the natural +attractiveness of his subject is not destroyed by his scientific handling of it."—<i>Literary +World</i> (Boston).</p> + +<blockquote><p>V. EVOLUTION AND DISEASE. By <span class="smcap">J. B. Sutton</span>, F.R.C.S. With +135 Illustrations.</p></blockquote> + +<p>"The work is of special value to professional men, yet educated persons +generally will find much in it which it is both interesting and important to +know."—<i>The Scottish Weekly.</i></p> + +<blockquote><p>VI. THE VILLAGE COMMUNITY. By <span class="smcap">G. L. Gomme</span>. Illustrated.</p></blockquote> + +<p>"His book will probably remain for some time the best work of reference +for facts bearing on those traces of the village community which have not +been effaced by conquest, encroachment, and the heavy hand of Roman law."—<i>Scottish +Leader.</i></p> + +<blockquote><p>VII. THE CRIMINAL. By <span class="smcap">Havelock Ellis</span>. Illustrated.</p></blockquote> + +<p>"An ably written, an instructive, and a most entertaining book."—<i>Law +Quarterly Review.</i></p> + +<hr class="tb" /> + +<p class="center">London: <span class="smcap">Walter Scott, Limited</span>, 24 Warwick Lane.</p> +<hr class="major" /> + +<h2>The Contemporary Science Series—continued.</h2> + +<blockquote><p>VIII. SANITY AND INSANITY. By Dr. <span class="smcap">Charles Mercier</span>. Illustrated.</p></blockquote> + +<p>"Taken as a whole, it is the brightest book on the physical side of mental +science published in our time."—<i>Pall Mall Gazette.</i></p> + +<blockquote><p>IX. HYPNOTISM. By Dr. <span class="smcap">Albert Moll</span>. Second Edition.</p></blockquote> + +<p>"Marks a step of some importance in the study of some difficult physiological +and psychological problems which have not yet received much attention +in the scientific world of England."—<i>Nature.</i></p> + +<blockquote><p>X. MANUAL TRAINING. By Dr. <span class="smcap">C. M. Woodward</span>, Director of the +Manual Training School, St. Louis. Illustrated.</p></blockquote> + +<p>"There is no greater authority on the subject than Professor Woodward."—<i>Manchester +Guardian.</i></p> + +<blockquote><p>XI. THE SCIENCE OF FAIRY TALES. By <span class="smcap">E. Sidney Hartland</span>.</p></blockquote> + +<p>"Mr. Hartland's book will win the sympathy of all earnest students, both +by the knowledge it displays, and by a thorough love and appreciation of his +subject, which is evident throughout."—<i>Spectator.</i></p> + +<blockquote><p>XII. PRIMITIVE FOLK. By <span class="smcap">Elie Reclus</span>.</p></blockquote> + +<p>"For an introduction to the study of the questions of property, marriage, +government, religion,—in a word, to the evolution of society,—this little +volume will be found most convenient."—<i>Scottish Leader.</i></p> + +<blockquote><p>XIII. THE EVOLUTION OF MARRIAGE. By Professor <span class="smcap">Letourneau</span>.</p></blockquote> + +<p>"Among the distinguished French students of sociology, Professor Letourneau +has long stood in the first rank. He approaches the great study of man +free from bias and shy of generalisations. To collect, scrutinise, and appraise +facts is his chief business."—<i>Science.</i></p> + +<blockquote><p>XIV. BACTERIA AND THEIR PRODUCTS. By Dr. <span class="smcap">G. Sims Woodhead</span>. +Illustrated.</p></blockquote> + +<p>"An excellent summary of the present state of knowledge of the subject."—<i>Lancet.</i></p> + +<blockquote><p>XV. EDUCATION AND HEREDITY. By <span class="smcap">J. M. Guyau</span>.</p></blockquote> + +<p>"It is a sign of the value of this book that the natural impulse on arriving +at its last page is to turn again to the first, and try to gather up and coordinate +some of the many admirable truths it presents."—<i>Anti-Jacobin.</i></p> + +<blockquote><p>XVI. THE MAN OF GENIUS. By Professor <span class="smcap">Lombroso</span>. Illustrated.</p></blockquote> + +<p>"By far the most comprehensive and fascinating collection of facts and +generalisations concerning genius which has yet been brought together."—<i>Journal +of Mental Science.</i></p> + +<blockquote><p>XVII. THE GRAMMAR OF SCIENCE. By Professor <span class="smcap">Karl Pearson</span>. +Illustrated.</p></blockquote> + +<blockquote><p>XVIII. PROPERTY: ITS ORIGIN AND DEVELOPMENT. By <span class="smcap">Ch. +Letourneau</span>, General Secretary to the Anthropological Society, Paris, +and Professor in the School of Anthropology, Paris.</p></blockquote> + +<p>An ethnological account of the beginnings of property among animals, of its +communistic stages among primitive races, and of its later individualistic developments, +together with a brief sketch of its probable evolution in the future.</p> + +<hr class="tb" /> + +<p class="center">London: <span class="smcap">Walter Scott, Limited</span>, 24 Warwick Lane.</p> + + + +<hr class="major" /> +<h2><a name="Transcribers_Notes" id="Transcribers_Notes"></a>Transcriber's Note:</h2> + + +<p>Changed what appeared to be upsilon with inverted breve to upsilon with +perispomeni in the Greek on page 2.</p> + +<p>Changed 'Kilarrea' to 'Kilauea' on page 19: Mauna Loa and Kilarrea.</p> + +<p>Changed 'Kilanea' to 'Kilauea' on page 39: Kilanea, 4158 feet.</p> + +<p>Made punctuation (semi-colons) consistent in caption to figure 16.</p> + +<p>Changed 'Brionde' to 'Brioude' on page 94: till at Brionde it becomes.</p> + +<p>Changed 'occuping' to 'occupying' on page 96: occuping a hollow.</p> + +<p>Changed 'Rodesberg' to 'Roderberg' on page 118: old extinct volcano +of Rodesberg.</p> + +<p>Changed 'Wolkenberg' to 'Wolkenburg' on page 118: and that of +the Wolkenberg.</p> + +<p>Left the reference to Jeremiah, l. 25. in footnote to Part III Chapter I, +although Jeremiah, li. 25. seems more appropriate.</p> + +<p>Changed 'fumarols' to 'fumaroles' on page 137: fumarols give evidence.</p> + +<p>Removed extra comma on page 153: of the present, epoch.</p> + +<p>Changed 'columnal' to 'columnar' on page 176: the columnal structure.</p> + +<p>Changed 'groves' to 'grooves' on page 183: the groves and scorings.</p> + +<p>Changed 'Angust' to 'August' on page 212: the 27th of Angust.</p> + +<p>Changed 'mikroskopischen' to 'mikroskopische' on page 260: +über mikroskopischen Structur.</p> + +<p>Changed 'become' to 'becomes' on page 260: the rock become a leucite-basalt.</p> + +<p>Left inconsistent spellings of +'Baalbec' and 'Baalbeck'; +'Harrat' and 'Harrât'; +'mètres' and 'metres'; +'pitchstone' and 'pitch-stone'; +'prehistoric' and 'pre-historic'; +'Rhône' and 'Rhone'; +'sub-aerial', 'subaërial' and 'subaerial'; +'tableland' and 'table-land'.</p> + +<p>Left the list numbering as is at the beginning of Chapter II of Part IV, +even though the list begins at item c, as if it continues the list which +began in the previous chapter.</p> + +<p>Footnotes were collected at the end of each chapter, and text was flowed +to move illustrations between paragraphs. +This has some effect on the index, since the referred-to text may have +been moved to a different page.</p> + +<p> </p> +<p> </p> +<hr class="full" /> +<p>***END OF THE PROJECT GUTENBERG EBOOK VOLCANOES: PAST AND PRESENT***</p> +<p>******* This file should be named 31627-h.txt or 31627-h.zip *******</p> +<p>This and all associated files of various formats will be found in:<br /> +<a href="http://www.gutenberg.org/dirs/3/1/6/2/31627">http://www.gutenberg.org/3/1/6/2/31627</a></p> +<p>Updated editions will replace the previous one--the old editions +will be renamed.</p> + +<p>Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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