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diff --git a/old/3772-h/files/ch13.html b/old/3772-h/files/ch13.html new file mode 100644 index 0000000..1ded52a --- /dev/null +++ b/old/3772-h/files/ch13.html @@ -0,0 +1,1120 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<!-- saved from url=(0036)http://../Lyell/The Student's Elements of Geology --> +<html> +<head> +<meta name="generator" content="HTML Tidy, see www.w3.org"> +<title>The Student's Elements of Geology: Title</title> +<meta content="text/html; charset=iso-8859-1" http-equiv= +"Content-Type"> +<meta content="MSHTML 5.00.2919.6307" name="GENERATOR"> +<link rel="stylesheet" href="geology.css" type="text/css"> +</head> +<body> +<p><b>The Student’s Elements of Geology</b></p> + +<hr> +<p class="page"><a name="page 189">[ 189 ]</a></p> + +<p> </p> + +<center> +<h3>TERTIARY OR CAINOZOIC PERIOD</h3> + +<hr width="40%"> +<br> +<br> +<b>Chapter XIII</b><br> +<br> +PLIOCENE PERIOD</center> + +<p class="intro">Glacial Formations of Pliocene Age. — +Bridlington Beds. — Glacial Drifts of Ireland. — Drift +of Norfolk Cliffs. — Cromer Forest-bed. — Aldeby and +Chillesford Beds. — Norwich Crag. — Older Pliocene +Strata. — Red Crag of Suffolk. — Coprolitic Bed of Red +Crag. — White or Coralline Crag. — Relative Age, +Origin, and Climate of the Crag Deposits. — Antwerp Crag. +— Newer Pliocene Strata of Sicily. — Newer Pliocene +Strata of the Upper Val d’Arno. — Older Pliocene of Italy. +— Subapennine Strata. — Older Pliocene Flora of +Italy.</p> + +<p>It will be seen in the description given in the last chapter of +the Post-pliocene formations of the British Isles that they +comprise a large proportion of those commonly termed glacial, +characterised by shells which, although referable to living +species, usually indicate a colder climate than that now belonging +to the latitudes where they occur fossil. But in parts of England, +more especially in Yorkshire, Norfolk, and Suffolk, there are +superficial formations of clay with glaciated boulders, and of sand +and pebbles, containing occasional, though rare, patches of shells, +in which the marine fauna begins to depart from that now inhabiting +the neighbouring sea, and comprises some species of mollusca not +yet known as living, as well as extinct varieties of others, +entitling us to class them as Newer Pliocene, although belonging to +the close of that period and chronologically on the verge of the +later or Post-pliocene epoch.</p> + +<p><b>Bridlington Drift.</b>—To this era belongs the +well-known locality of Bridlington, near the mouth of the Humber, +in Yorkshire, where about seventy species or well-marked varieties +of shells have been found on the coast, near the sea-level, in a +bed of sand several feet thick resting on glacial clay with much +chalk débris, and covered by a deposit of purple clay with +glaciated boulders. More than a third of the species in this drift +are now inhabitants of arctic regions, none of them extending +southward to the British seas; which is the more remarkable as +Bridlington is situated in lat. 54°</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 190">[ 190 ]</a></p> + +<p>north. Fifteen species are British and Arctic, a very few belong +to those species which range south of our British seas. Five +species or well-marked varieties are not known living, namely, the +variety of <i>Astarte borealis</i> (called <i>A. Withami</i>); <i> +A. mutabilis</i>; the sinistral form of <i>Tritonium carinatum, +Cardita analis,</i> and <i>Tellina obliqua,</i> Fig. 120, p. 194. +Mr. Searles Wood also inclines to consider <i>Nucula +Cobboldiæ,</i> Fig. 119, p. 194, now absent from the European +seas and the Atlantic, as specifically distinct from a +closely-allied shell now living in the seas surrounding Vancouver’s +Island, which some conchologists regard as a variety. <i>Tellina +obliqua</i> also approaches very near to a shell now living in +Japan.</p> + +<p><b>Glacial Drift of Ireland.</b>—Marine drift containing +the last-mentioned Nucula and other glacial shells reaches a height +of from 1000 to 1200 feet in the county of Wexford, south of +Dublin. More than eighty species have already been obtained from +this formation, of which two, <i>Conovulus pyramidalis</i> and <i> +Nassa monensis,</i> are not known as living; while <i>Turritella +incrassata</i> and <i>Cypræa lucida</i> no longer inhabit the +British seas, but occur in the Mediterranean. The great elevation +of these shells, and the still greater height to which the surface +of the rocks in the mountainous regions of Ireland have been +smoothed and striated by ice-action, has led geologists to the +opinion that that island, like the greater part of England and +Scotland, after having been united with the continent of Europe, +from whence it received the plants and animals now inhabiting it, +was in great part submerged. The conversion of this and other parts +of Great Britain into an archipelago was followed by a re-elevation +of land and a second continental period. After all these changes +the final separation of Ireland from Great Britain took place, and +this event has been supposed to have preceded the opening of the +straits of Dover.*</p> + +<img src="../images1/fig116.jpg" width="252" height="116" alt= +"Fig. 116: Tellina balthica" align="left"> + +<p><b>Drift of Norfolk Cliffs.</b>—There are deposits of +boulder clay and till in the Norfolk cliffs principally made up of +the waste of white chalk and flints which, in the opinion of Mr. +Searles Wood, jun., and others, are older than the Bridlington +drift, and contain a larger proportion of shells common to the +Norwich and Red Crag, including a certain number</p> + +<p class="fnote">* See Antiquity of Man, chap. xiv.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 191">[ 191 ]</a></p> + +<p>of extinct forms, but also abounding in <i>Tellina balthica</i> +(<i>T. solidula,</i> Fig. 116), which is found fossil at +Bridlington, and living in our British seas, but wanting in all the +formations, even the newest, afterwards to be described as Crag. As +the greater part of these drifts are barren of organic remains, +their classification is at present a matter of great +uncertainty.</p> + +<p>They can nowhere be so advantageously studied as on the coast +between Happisburgh and Cromer. Here we may see vertical cliffs, +sometimes 300 feet and more in height, exposed for a distance of +fifty miles, at the base of which the chalk with flints crops out +in nearly horizontal strata. Beds of gravel and sand repose on this +undisturbed chalk. They are often strangely contorted, and envelop +huge masses or erratics of chalk with layers of vertical flint. I +measured one of these fragments in 1839 at Sherringham, and found +it to be eighty feet in its longest diameter. It has been since +entirely removed by the waves of the sea. In the floor of the chalk +beneath it the layers of flint were horizontal. Such erratics have +evidently been moved bodily from their original site, probably by +the same glacial action which has polished and striated some of the +accompanying granitic and other boulders, occasionally six feet in +diameter, which are imbedded in the drift.</p> + +<p><b>Cromer Forest-bed.</b>—Intervening between these +glacial formations and the subjacent chalk lies what has been +called the Cromer Forest-bed. This buried forest has been traced +from Cromer to near Kessingland, a distance of more than forty +miles, being exposed at certain seasons between high and low water +mark. It is the remains of an old land and estuarine deposit, +containing the submerged stumps of trees standing erect with their +roots in the ancient soil. Associated with the stumps and overlying +them, are lignite beds with fresh-water shells of recent species, +and laminated clay without fossils. Through the lignite and +forest-bed are scattered cones of the Scotch and spruce firs with +the seeds of recent plants, and the bones of at least twenty +species of terrestrial mammalia. Among these are two species of +elephant, <i>E. meridionalis,</i> Nesti, and <i>E. antiquus,</i> +the former found in the Newer Pliocene beds of the Val d’Arno, near +Florence. In the same bed occur <i>Hippopotamus major, Rhinoceros +etruscus,</i> both of them also Val d’Arno species, many species of +deer considered by Mr. Boyd Dawkins to be characteristic of warmer +countries, and also a horse, beaver, and field-mouse. Half of these +mammalia are extinct, and the rest still survive in Europe. The +vegetation taken alone</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 192">[ 192 ]</a></p> + +<p>does not imply a temperature higher than that now prevailing in +the British Isles. There must have been a subsidence of the forest +to the amount of 400 or 500 feet, and a re-elevation of the same to +an equal extent in order to allow the ancient surface of the chalk +or covering of soil, on which the forest grew, to be first covered +with several hundred feet of drift, and then upheaved so that the +trees should reach their present level. Although the relative +antiquity of the forest-bed to the overlying glacial till is clear, +there is some difference of opinion as to its relation to the crag +presently to be described.</p> + +<img src="../images1/fig117.jpg" width="89" height="133" alt= +"Fig. 117: Natica helicoides" align="left"> + +<p><b>Chillesford and Aldeby Beds.</b>—It is in the counties +of Norfolk, Suffolk, and Essex, that we obtain our most valuable +information respecting the British Pliocene strata, whether newer +or older. They have obtained in those counties the provincial name +of “Crag,” applied particularly to masses of shelly sand which have +long been used in agriculture to fertilise soils deficient in +calcareous matter. At Chillesford, between Woodbridge and +Aldborough in Suffolk, and Aldeby, near Beccles, in the same +county, there occur stratified deposits, apparently older than any +of the preceding drifts of Yorkshire, Norfolk, and Suffolk. They +are composed at Chillesford of yellow sands and clays, with much +mica, forming horizontal beds about twenty feet thick. Messrs. +Prestwich and Searles Wood, senior, who first described these beds, +point out that the shells indicate on the whole a colder climate +than the Red Crag; two-thirds of them being characteristic of high +latitudes. Among these are <i>Cardium Grœnlandicum, Leda +limatula, Tritonium carinatum,</i> and <i>Scalaria +Grœnlandica.</i> In the upper part of the laminated clays a +skeleton of a whale was found associated with casts of the +characteristic shells, <i>Nucula Cobboldiæ</i> and <i>Tellina +obliqua,</i> already referred to as no longer inhabiting our seas, +and as being extinct varieties if not species. The same shells +occur in a perfect state in the lower part of the formation. <i> +Natica helicoides</i> (Fig. 117) is an example of a species +formerly known only as fossil, but which has now been found living +in our seas.</p> + +<p>At Aldeby, where beds occur decidedly similar in mineral +character as well as fossil remains, Messrs. Crowfoot and Dowson +have now obtained sixty-six species of mollusca, comprising the +Chillesford species and some others. Of these about nine-tenths are +recent. They are in a perfect state, clearly indicating a cold +climate; as two-thirds of them are now met with in arctic</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 193">[ 193 ]</a></p> + +<p>regions. As a rule, the lamellibranchiate molluscs have both +valves united, and many of them, such as <i>Mya arenaria,</i> stand +with the siphonal end upward, as when in a living state. <i>Tellina +balthica,</i> before mentioned (Fig. 116) as so characteristic of +the glacial beds, including the drift of Bridlington, has not yet +been found in deposits of Chillesford and Aldeby age, whether at +Sudbourn, East Bavent, Horstead, Coltishall, Burgh, or in the +highest beds overlying the Norwich Crag proper at Bramerton and +Thorpe.</p> + +<center><img src="../images1/fig118.jpg" width="374" height="259" alt= +"Fig. 118: <i>Mastodon arvernensis,</i> third milk molar, left side, upper jaw: grinding surface. Norwich Crag, Postwick, also found in Red Crag, see p. 197."> +</center> + +<p><b>Norwich or Fluvio-marine Crag.</b>—The beds above +alluded to ought, perhaps, to be regarded as beds of passage +between the glacial formations and those called from a provincial +name “Crag,” the newest member of which has been commonly called +the “Norwich Crag.” It is chiefly seen in the neighbourhood of +Norwich, and consists of beds of incoherent sand, loam, and gravel, +which are exposed to view on both banks of the Yare, as at +Bramerton and Thorpe. As they contain a mixture of marine, land, +and fresh-water shells, with bones of fish and mammalia, it is +clear that these beds have been accumulated at the bottom of a sea +near the mouth of a river. They form patches rarely exceeding +twenty feet in thickness, resting on white chalk. At their junction +with the chalk there invariably intervenes a bed called the +“Stone-bed,” composed of unrolled chalk-flints, commonly of large +size, mingled with the remains of a land fauna comprising <i> +Mastodon arvernensis, Elephas meridionalis,</i> and an extinct +species of deer. The mastodon, which is a species characteristic of +the Pliocene strata of Italy and France, is the most abundant +fossil, and one not found in the</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 194">[ 194 ]</a></p> + +<p>Cromer forest before mentioned. When these flints, probably long +exposed in the atmosphere, became submerged, they were covered with +barnacles, and the surface of the chalk became perforated by the +<i>Pholas crispata,</i> each fossil shell still remaining at the +bottom of its cylindrical cavity, now filled up with loose sand +from the incumbent crag. This species of Pholas still exists, and +drills the rocks between high and low water on the British coast. +The name of “Fluvio-marine” has often been given to this formation, +as no less than twenty species of land and fresh-water shells have +been found in it. They are all of living species; at least only one +univalve, <i>Paludina lenta,</i> has any, and that a very doubtful, +claim to be regarded as extinct.</p> + +<center><img src="../images1/fig119.jpg" width="335" height="123" alt= +"Fig. 119: Nucula Cobboldiæ; Fig. 120: Tellina obliqua."> +</center> + +<p>Of the marine shells, 124 in number, about 18 per cent are +extinct, according to the latest estimate given me by Mr. Searles +Wood; but, for reasons presently to be mentioned, this percentage +must be only regarded as provisional. It must also be borne in mind +that the proportion of recent shells would be augmented if the +uppermost beds at Bramerton, near Norwich, which belong to the most +modern or Chillesford division of the Crag, had been included, as +they were formerly, by Mr. Woodward and myself, in the Norwich +series. Arctic shells, which formed so large a proportion in the +Chillesford and Aldeby beds, are more rare in the Norwich Crag, +though many northern species--such as <i>Rhynchonella psittacea, +Scalaria Grœnlandica, Astarte borealis, Panopæa +Norvegia,</i> and others--still occur. The <i>Nucula +Cobboldiæ</i> and <i>Tellina obliqua,</i> Figs. 119 and 120, +before mentioned, p. 194, are frequent in these beds, as are also +<i>Littorina littorea, Cardium edule,</i> and <i>Turritella +communis,</i> of our seas, proving the littoral origin of the +beds.</p> + +<br> + + +<center>OLDER PLIOCENE STRATA.</center> + +<p><b>Red Crag.</b>—Among the English Pliocene beds the next +in antiquity is the Red Crag, which often rests immediately on the +London Clay, as in the county of Essex, illustrated in Fig. +121.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 195">[ 195 ]</a></p> + +<center><img src="../images1/fig121.jpg" width="339" height="76" alt= +" Fig. 121: Red Crag, London clay and chalk."></center> + +<p>It is chiefly in the county of Suffolk that it is found, rarely +exceeding twenty feet in thickness, and sometimes overlying another +Pliocene deposit, the Coralline Crag, to be mentioned in the +sequel. It has yielded--exclusive of 25 species regarded by Mr. +Wood as derivative--256 species of mollusca, of which 65, or 25 per +cent, are extinct. Thus, apart from its order of superposition, its +greater antiquity than the Norwich and glacial beds, already +described, is proved by the greater departure from the fauna of our +seas. It may also be observed that in most of the deposits of this +Red Crag, the northern forms of the Norwich Crag, and of such +glacial formations as Bridlington, are less numerous, while those +having a more southern aspect begin to make their appearance. Both +the quartzose sand, of which it chiefly consists, and the included +shells, are most commonly distinguished by a deep ferruginous or +ochreous colour, whence its name. The shells are often rolled, +sometimes comminuted, and the beds have much the appearance of +having been shifting sand-banks, like those now forming on the +Dogger-bank, in the sea, sixty miles east of the coast of +Northumberland. Cross stratification is almost always present, the +planes of the strata being sometimes directed towards one point of +the compass, sometimes to the opposite, in beds immediately +overlying. That such a structure is not deceptive or due to any +subsequent concretionary rearrangement of particles, or to mere +bands of colour produced by the iron, is proved by each bed being +made up of flat pieces of shell which lie parallel to the planes of +the smaller strata.</p> + +<p>It has long been suspected that the different patches of Red +Crag are not all of the same age, although their chronological +relation can not be decided by superposition. Separate masses are +characterised by shells specifically distinct or greatly varying in +relative abundance, in a manner implying that the deposits +containing them were separated by intervals of time. At Butley, +Tunstall, Sudbourn, and in the Red Crag of Chillesford, the +mollusca appear to assume their most modern aspect when the climate +was colder than when the earliest deposits of the same period were +formed. At Butley, <i>Nucula Cobboldiæ</i>, so common in the +Norwich and certain glacial beds, is found, and <i>Purpura +tetragona</i> (Fig. 122) is very abundant. On the other hand, at +Walton-on-</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 196">[ 196 ]</a></p> + +<img src="../images1/fig122.jpg" width="97" height="208" alt= +"Fig. 122: Purpura tetragona." align="left"> + +<p>the-Naze, in Essex, we seem to have an exhibition of the oldest +phase of the Red Crag; and a warmer climate seems indicated, not +only by the absence of many northern forms, but also by the +abundance of some now living in the British seas and the +Mediterranean. <i>Voluta Lamberti</i> (see Figs. 123 and 124), an +extinct form, which seems to have flourished chiefly in the +antecedent Coralline Crag period, is still represented here by +individuals of every age.</p> + +<p>The reversed whelk (Fig. 125) is common at Walton, where the +dextral form of that shell is unknown. Here also we find most +frequently specimens of lamellibranchiate molluscs, with both the +valves united, showing that they belonged to this sea of the Upper +Crag, and were not washed in from an older bed, such as the +Coralline, in which case the ligament would not have held together +the valves in strata so often showing signs of the boisterous +action of the waves. No less than forty species of +lamellibranchiate molluscs, with double valves, have been collected +by Mr. Bell from the various localities of the Red Crag.</p> + +<center><img src="../images1/fig123.jpg" width="353" height="329" alt= +"Fig. 123: Voluta Lamberti; Fig. 124: Voluta Lamberti; Fig. 125: Trophon antiquum."> +</center> + +<p>At and near the base of the Red Crag is a loose bed of</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 197">[ 197 ]</a></p> + +<p>brown nodules, first noticed by Professor Henslow as containing +a large percentage of earthy phosphates. This bed of coprolites (as +it is called, because they were originally supposed to be the +fæces of animals) does not always occur at one level, but is +generally in largest quantity at the junction of the Crag and the +underlying formation. In thickness it usually varies from six to +eighteen inches, and in some rare cases amounts to many feet. It +has been much used in agriculture for manure, as not only the +nodules, but many of the separate bones associated with them, are +largely impregnated with phosphate of lime, of which there is +sometimes as much as sixty per cent. They are not unfrequently +covered with barnacles, showing that they were not formed as +concretions in the stratum where they now lie buried, but had been +previously consolidated. The phosphatic nodules often collect +fossil crabs and fishes from the London Clay, together with the +teeth of gigantic sharks. In the same bed have been found many +ear-bones of whales, and the teeth of <i>Mastodon arvernensis, +Rhinoceros Schleiermacheri, Tapirus priscus,</i> and Hipparion (a +quadruped of the horse family), and antlers of a stag, <i>Cervus +anoceros.</i> Organic remains also of the older chalk and Lias are +met with, showing how great was the denudation of previous +formations during the Pliocene period. As the older White Crag, +presently to be mentioned, contains similar phosphatic nodules near +its base, those of the Red Crag may be partly derived from this +source.</p> + +<p><b>White or Coralline Crag.</b>—The lower or Coralline +Crag is of very limited extent, ranging over an area about twenty +miles in length, and three or four in breadth, between the rivers +Stour and Alde, in Suffolk. It is generally calcareous and +marly--often a mass of comminuted shells, and the remains of +bryozoa* (or polyzoa), passing occasionally into a soft +building-stone. At Sudbourn and Gedgrave, near Orford, this +building-stone has been largely quarried. At some places in the +neighbourhood the softer mass is divided by thin flags of hard +limestone, and bryozoa placed in the upright position in which they +grew. From the abundance of these coralloid mollusca the lowest or +White Crag obtained its popular name, but true corals, as now +defined, or zoantharia, are very rare in this formation.</p> + +<p class="fnote">* Ehrenberg proposed in 1831 the term <i> +Bryozoum</i>, or “Moss-animal,” for the molluscous or ascidian form +of polyp, characterised by having two openings to the digestive +sack, as in <i>Eschara, Flustra, Retepora,</i> and other zoophytes +popularly included in the corals, but now classed by naturalists as +mollusca. The term <i>Polyzoum,</i> synonymous with <i> +Bryozoum,</i> was, it seems, proposed in 1830, or the year before, +by Mr. J. O. Thompson.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 198">[ 198 ]</a></p> + +<p>The Coralline Crag rarely, if ever, attains a thickness of +thirty feet in any one section. Mr. Prestwich imagines that if the +beds found at different localities were united in the probable +order of their succession, they might exceed eighty feet in +thickness, but Mr. Searles Wood does not believe in the possibility +of establishing such a chronological succession by aid of the +organic remains, and questions whether proof could be obtained of +more than forty feet. I was unable to come to any satisfactory +opinion on the subject, although at Orford, especially at Gedgrave, +in the neighbourhood of that place, I saw many sections in pits, +where this crag is cut through. These pits are so unconnected, and +of such limited extent, that no continuous section of any length +can be obtained, so that speculations as to the thickness of the +whole deposit must be very vague. At the base of the formation at +Sutton a bed of phosphatic nodules, very similar to that before +alluded to in the Red Crag, with remains of mammalia, has been met +with.</p> + +<center><img src="../images1/fig126.jpg" width="336" height="107" alt= +"Fig. 126: Section near Woodbridge, in Suffolk."></center> + +<p>Whenever the Red and Coralline Crag occur in the same district, +the Red Crag lies uppermost; and in some cases, as in the section +represented in Fig. 126, which I had an opportunity of seeing +exposed to view in 1839, it is clear that the older deposit, or +Coralline Crag, <i>b</i>, had suffered denudation, before the newer +formation, <i>a</i>, was thrown down upon it. At D there was not +only seen a distinct cliff, eight or ten feet high, of Coralline +Crag, running in a direction N.E. and S.W., against which the Red +Crag abuts with its horizontal layers, but this cliff occasionally +overhangs. The rock composing it is drilled everywhere by <i> +Pholades</i>, the holes which they perforated having been +afterwards filled with sand, and covered over when the newer beds +were thrown down. The older formation is shown by its fossils to +have accumulated in a deeper sea, and contains none of those +littoral forms such as the limpet, <i>Patella</i>, found in the Red +Crag. So great an amount of denudation could scarcely take place, +in such incoherent materials, without some of the fossils of the +inferior beds becoming mixed up with the overlying crag, so that +considerable difficulty must be occasionally experienced by</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 199">[ 199 ]</a></p> + +<p>the palæontologist in deciding which species belong +severally to each group.</p> + +<center><img src="../images1/fig127.jpg" width="403" height="440" alt= +"Fig. 127: Fascicularia aurantium, from the inferior or Coralline Crag, Suffolk. Fig. 128: Astarte Omalii, species common to Upper and Lower Crag."> +</center> + +<p>Mr. Searles Wood estimates the total number of marine testaceous +mollusca of the Coralline Crag at 350, of which 110 are not known +as living, being in the proportion of thirty-one per cent extinct. +No less than 130 species of bryozoa have been found in the +Coralline Crag, and some belong to genera unknown in the living +creation, and of a very peculiar structure; as, for example, that +represented in Fig. 127, which is one of several species having a +globular form. Among the testacea the genus <i>Astarte</i> (see +Fig. 128) is largely represented, no less than fourteen species +being known, and many of these being rich in individuals. There is +an absence of genera peculiar to hot climates, such as <i>Conus, +Oliva, Fasciolaria, Crassatella</i>, and others. The absence also +of large cowries (<i>Cyprea</i>), those found belonging</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 200">[ 200 ]</a></p> + +<p>exclusively to the section <i>Trivia</i>, is remarkable. The +large volute, called <i>Voluta Lamberti</i> (Fig. 123, p. 196), may +seem an exception; but it differs in form from the volutes of the +torrid zone, and, like the living <i>Voluta Magellanica</i>, must +have been fitted for an extra-tropical climate.</p> + +<center><img src="../images1/fig129.jpg" width="410" height="184" alt= +"Fig. 129: Lingula Dumortieri. Fig. 130: Pyrula reticulata. Fig. 131: Temnechinus excavatus."> +</center> + +<p>The occurrence of a species of <i>Lingula</i> at Sutton (see +Fig. 129) is worthy of remark, as these <i>Brachiopoda</i> seem now +confined to more equatorial latitudes; and the same may be said +still more decidedly of a species of <i>Pyrula</i>, supposed by Mr. +Wood to be identical with <i>P. reticulata</i> (Fig. 130), now +living in the Indian Ocean. A genus also of echinoderms, called by +Professor Forbes <i>Temnechinus</i> (Fig. 131), occurs in the Red +and Coralline Crag of Suffolk, and until lately was unknown in a +living state, but it has been brought to light as an existing form +by the deep-sea dredgings, both of the United States survey, off +Florida, at a depth of from 180 to 480 feet, and more recently +(1869), in the British seas, during the explorations of the +“Porcupine.”</p> + +<p><b>Climate of the Crag Deposits.</b>—One of the most +interesting conclusions deduced from a careful comparison of the +shells of the British Pliocene strata and the fauna of our present +seas has been pointed out by Professor E. Forbes. It appears that, +during the Glacial period, a period intermediate, as we have seen, +between that of the Crag and our own time, many shells, previously +established in the temperate zone, retreated southward to avoid an +uncongenial climate, and they have been found fossil in the Newer +Pliocene strata of Sicily, Southern Italy, and the Grecian +Archipelago, where they may have enjoyed, during the era of +floating icebergs, a climate resembling that now prevailing in +higher European latitudes.* The Professor gave a list of fifty +shells which inhabited the British seas while the Coralline and Red +Crag were forming, and which, though now living in our seas,</p> + +<p class="fnote">* E. Forbes Mem. Geol. Survey of Gt. Brit., vol. +i, p. 386.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 201">[ 201 ]</a></p> + +<p>were wanting, as far as was then known, in the glacial deposits. +Some few of these species have subsequently been found in the +glacial drift, but the general conclusion of Forbes remains +unshaken.</p> + +<p>The transport of blocks by ice, when the Red Crag was being +deposited, appears to me evident from the large size of some huge, +irregular, quite unrounded chalk flints, retaining their white +coating, and 2 feet long by 18 inches broad, in beds worked for +phosphatic nodules at Foxhall, four miles south-east of Ipswich. +These must have been tranquilly drifted to the spot by floating +ice. Mr. Prestwich also mentions the occurrence of a large block of +porphyry in the base of the Coralline Crag at Sutton, which would +imply that the ice-action had begun in our seas even in this older +period. The cold seems to have gone on increasing from the time of +the Coralline to that of the Norwich Crag, and became more and more +severe, not perhaps without some oscillations of temperature, until +it reached its maximum in what has been called the Glacial period, +or at the close of the Newer Pliocene, and in the Post-pliocene +periods.</p> + +<p><b>Relation of the Fauna of the Crag to that of the recent +Seas.</b>—By far the greater number of the recent marine +species occurring in the several Crag formations are still +inhabitants of the British seas; but even these differ considerably +in their relative abundance, some of the commonest of the Crag +shells being now extremely scarce--as, for example, <i>Buccinum +Dalei</i>--while others, rarely met with in a fossil state, are now +very common, as <i>Murex erinaceus</i> and <i>Cardium +echinatum.</i> Some of the species also, the identity of which with +the living would not be disputed by any conchologist, are +nevertheless distinguishable as varieties, whether by slight +deviations in form or a difference in average dimensions. Since Mr. +Searles Wood first described the marine testacea of the Crags, the +additions made to that fossil fauna have not been considerable, +whereas we have made in the same period immense progress in our +knowledge of the living testacea of the British and arctic seas, +and of the Mediterranean. By this means the naturalist has been +enabled to identify with existing species many forms previously +supposed to be extinct.</p> + +<p>In the forthcoming supplement to the invaluable monograph +communicated by Mr. Wood to the Palæontographical Society, in +which he has completed his figures and descriptions of the British +crag shells of every age, list will be found of all the fossil +shells, of which a summary is given in the table, p. 202.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 202">[ 202 ]</a></p> + +<p>To begin with the uppermost or Chillesford beds, it will be seen +that about 9 per cent only are extinct, or not known as living, +whereas in the Norwich, which succeeds in the descending order, +seventeen in a hundred are extinct. Formerly, when the Norwich or +Fluvio-marine Crag was spoken of, both these formations were +included under the same head, for both at Bramerton and Thorpe, the +chief localities where the Norwich Crag was studied, an overlying +deposit occurs referable to the Chillesford age. If now the two +were fused together as of old, their shells would, according to Mr. +Wood, yield a percentage of fifteen in a hundred of species extinct +or not known as living.</p> + +<center>NUMBER OF KNOWN SPECIES OF MARINE TESTACEA<br> +IN THE CRAG<br> +<br> +<table border="1" cellpadding="4" cellspacing="0" width="60%" summary="Column 2: Total number, Column 3: Not known as living, Column 4: Percentage of Shells not known as living"> +<tr> +<td align="center" colspan="4"><small>CHILLESFORD AND ALDEBY +BEDS</small></td> +</tr> + +<tr> +<td align="left"> </td> +<td align="center" valign="bottom">Total<br> +number</td> +<td align="center" valign="bottom">Not known<br> +as living</td> +<td align="center" valign="bottom">Percentage of<br> +Shells not known<br> +as living</td> +</tr> + +<tr> +<td align="left">Bivalves</td> +<td align="center"> 61</td> +<td align="center"> 4</td> +<td align="center" valign="middle" rowspan="3"> +9·5</td> +</tr> + +<tr> +<td align="left">Univalves</td> +<td align="center"> 33</td> +<td align="center"> 5</td> +</tr> + +<tr> +<td align="left">Brachiopods</td> +<td align="center"> 0</td> +<td align="center"> 0</td> +</tr> + +<tr> +<td align="center" colspan="4"><small>NORWICH OR FLUVIO-MARINE +CRAG</small></td> +</tr> + +<tr> +<td align="left">Bivalves</td> +<td align="center"> 61</td> +<td align="center">10</td> +<td align="center" valign="middle" rowspan="3">17·5</td> +</tr> + +<tr> +<td align="left">Univalves</td> +<td align="center"> 64</td> +<td align="center">12</td> +</tr> + +<tr> +<td align="left">Brachiopods</td> +<td align="center"> 1</td> +<td align="center"> 0</td> +</tr> + +<tr> +<td align="center" colspan="4"><small>RED CRAG<br> +<i>(Exclusive to many derivative shells)</i></small></td> +</tr> + +<tr> +<td align="left">Bivalves</td> +<td align="center">128</td> +<td align="center">31</td> +<td align="center" valign="middle" rowspan="3">25·0</td> +</tr> + +<tr> +<td align="left">Univalves</td> +<td align="center">127</td> +<td align="center">33</td> +</tr> + +<tr> +<td align="left">Brachiopods</td> +<td align="center"> 1</td> +<td align="center"> 1</td> +</tr> + +<tr> +<td align="center" colspan="4"><small>CORALLINE CRAG</small></td> +</tr> + +<tr> +<td align="left">Bivalves</td> +<td align="center">161</td> +<td align="center">47</td> +<td align="center" valign="middle" rowspan="3">31·5</td> +</tr> + +<tr> +<td align="left">Univalves</td> +<td align="center">184</td> +<td align="center">60</td> +</tr> + +<tr> +<td align="left">Brachiopods</td> +<td align="center"> 5</td> +<td align="center"> 3</td> +</tr> +</table> +</center> + +<p>To come next to the Red Crag, the reader will observe that a +percentage of 25 is given of shells unknown as living, and this +increases to 31 in the antecedent Coralline Crag. But the gap +between these two stages of our Pliocene deposits is really wider +than these numbers would indicate, for several reasons. In the +first place, the Coralline Crag is more strictly the product of a +single period, the Red Crag, as we have seen, consisting of +separate and independent patches, slightly varying in age, of which +the newest is probably not much anterior to the Norwich Crag. +Secondly, there was a great change of conditions, both as to +the</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 203">[ 203 ]</a></p> + +<p>depth of the sea and climate, between the periods of the +Coralline and Red Crag, causing the fauna in each to differ far +more widely than would appear from the above numerical results.</p> + +<p>The value of the analysis given in the above table of the shells +of the Red and Coralline Crags is in no small degree enhanced by +the fact that they were all either collected by Mr. Wood himself, +or obtained by him direct from their discoverers, so that he was +enabled in each case to test their authenticity, and as far as +possible to avoid those errors which arise from confounding +together shells belonging to the sea of a newer deposit, and those +washed into it from a formation of older date. The danger of this +confusion may be conceived when we remember that the number of +species rejected from the Red Crag as derivative by Mr. Wood is no +less than 25. Some geologists have held that on the same grounds it +is necessary to exclude as spurious some of the species found in +the Norwich Crag proper; but Mr. Wood does not entertain this view, +believing that the spurious shells which have sometimes found their +way into the lists of this crag have been introduced by want of +care from strata of Red Crag.</p> + +<p>There can be no doubt, on the other hand, that conchologists +have occasionally rejected from the Red and Norwich Crags, as +derivative, shells which really belonged to the seas of those +periods, because they were extinct or unknown as living, which in +their eyes afforded sufficient ground for suspecting them to be +intruders. The derivative origin of a species may sometimes be +indicated by the extreme scarcity of the individuals, their colour, +and worn condition; whereas an opposite conclusion may be arrived +at by the integrity of the shells, especially when they are of +delicate and tender structure, or their abundance, and, in the case +of the lamellibranchiata, by their being held together by the +ligament, which often happens when the shells have been so broken +that little more than the hinges of the two valves are preserved. +As to the univalves, I have seen from a pit of Red Crag, near +Woodbridge, a large individual of the extinct <i>Voluta +Lamberti</i>, seven inches in length, of which the lip, then +perfect, had in former stages of its growth been frequently broken, +and as often repaired. It had evidently lived in the sea of the Red +Crag, where it had been exposed to rough usage, and sustained +injuries like those which the reversed whelk, <i>Trophon +antiquum</i>, so characteristic of the same formation, often +exhibits. Additional proofs, however, have lately been obtained by +Mr. Searles Wood that this</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 204">[ 204 ]</a></p> + +<p>shell had not died out in the era of the Red Crag by the +discovery of the same fossil near Southwold, in beds of the later +Norwich Crag.</p> + +<p><b>Antwerp Crag.</b>—Strata of the same age as the Red and +Coralline Crag of Suffolk have been long known in the country round +Antwerp, and on the banks of the Scheldt, below that city; and the +lowest division, or Black Crag, there found, is shown by the shells +to be somewhat more ancient than any of our British series, and +probably forms the first links of a downward passage from the +strata of the Pliocene to those of the Upper Miocene period.</p> + +<img src="../images1/fig132.jpg" width="90" height="213" alt= +"Fig. 132: Murex vaginatus" align="left"> + +<p><b>Newer Pliocene Strata of Sicily.</b>—At several points +north of Catania, on the eastern sea-coast of Sicily--as at +Aci-Castello, for example, Trezza, and Nizzeti--marine strata, +associated with volcanic tuffs and basaltic lavas, are seen, which +belong to a period when the first igneous eruptions of Mount Etna +were taking place in a shallow bay of the Mediterranean. They +contain numerous fossil shells, and out of 142 species that have +been collected all but eleven are identical with species now +living. Some few of these eleven shells may possibly still linger +in the depths of the Mediterranean, like <i>Murex vaginatus</i>, +see Fig. 132. The last-mentioned shell had already become rare when +the associated marine and volcanic strata above alluded to were +formed. On the whole, the modern character of the testaceous fauna +under consideration is expressed not only by the small proportion +of extinct species, but by the relative number of individuals by +which most of the other species are represented, for the proportion +agrees with that observed in the present fauna of the +Mediterranean. The rarity of individuals in the extinct species is +such as to imply that they were already on the point of dying out, +having flourished chiefly in the earlier Pliocene times, when the +Subapennine strata were in progress.</p> + +<p>Yet since the accumulation of these Newer Pliocene sands and +clays, the whole cone of Etna, 11,000 feet in height and about 90 +miles in circumference at its base, has been slowly built up; an +operation requiring many tens of thousands of years for its +accomplishment, and to estimate the magnitude of which it is +necessary to study in detail the internal structure of the +mountain, and to see the proofs of its double axis, or the evidence +of the lavas of the present great centre of eruption having +gradually overwhelmed and enveloped a</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 205">[ 205 ]</a></p> + +<p>more ancient cone, situated 3½ miles to the east of the +present one.*</p> + +<p>It appears that while Etna was increasing in bulk by a series of +eruptions, its whole mass, comprising the foundations of subaqueous +origin above alluded to, was undergoing a slow upheaval, by which +those marine strata were raised to the height of 1200 feet above +the sea, as seen at Catera, and perhaps to greater heights, for we +can not trace their extension westward, owing to the dense and +continuous covering of modern lava under which they are buried. +During the gradual rise of these Newer Pliocene formations +(consisting of clays, sands, and basalts) other strata of +Post-pliocene date, marine as well as fluviatile, accumulated round +the base of the mountain, and these, in their turn, partook of the +upward movement, so that several inland cliffs and terraces at low +levels, due partly to the action of the sea and partly to the river +Simeto, originated in succession. Fossil remains of the elephant, +and other extinct quadrupeds, have been found in these +Post-Pliocene strata, associated with recent shells.</p> + +<p>There is probably no part of Europe where the Newer Pliocene +formations enter so largely into the structure of the earth’s +crust, or rise to such heights above the level of the sea, as +Sicily. They cover nearly half the island, and near its centre, at +Castrogiovanni, reach an elevation of 3000 feet. They consist +principally of two divisions, the upper calcareous and the lower +argillaceous, both of which may be seen at Syracuse, Girgenti, and +Castrogiovanni. According to Philippi, to whom we are indebted for +the best account of the tertiary shells of this island, thirty-five +species out of one hundred and twenty-four obtained from the beds +in central Sicily are extinct.</p> + +<p>A geologist, accustomed to see nearly all the Newer Pliocene +formations in the north of Europe occupying low grounds and very +incoherent in texture, is naturally surprised to behold formations +of the same age so solid and stony, of such thickness, and +attaining so great an elevation above the level of the sea. The +upper or calcareous member of this group in Sicily consists in some +places of a yellowish-white stone, like the Calcaire Grossier of +Paris; in others, of a rock nearly as compact as marble. Its +aggregate thickness amounts sometimes to 700 or 800 feet. It +usually occurs in regular horizontal beds, and is occasionally +intersected by deep valleys, such as those of Sortino and +Pentalica,</p> + +<p class="fnote">* See a Memoir on the Lavas and Mode of Origin of +Mount Etna by the Author in Phil. Trans., 1858.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 206">[ 206 ]</a></p> + +<p>in which are numerous caverns. The fossils are in every stage of +preservation, from shells retaining portions of their animal matter +and colour to others which are mere casts. The limestone passes +downward into a sandstone and conglomerate, below which is clay and +blue marl, from which perfect shells and corals may be disengaged. +The clay sometimes alternates with yellow sand.</p> + +<p>South of the plain of Catania is a region in which the tertiary +beds are intermixed with volcanic matter, which has been for the +most part the product of submarine eruptions. It appears that, +while the clay, sand, and yellow limestone before mentioned were in +course of deposition at the bottom of the sea, volcanoes burst out +beneath the waters, like that of Graham Island, in 1831, and these +explosions recurred again and again at distant intervals of time. +Volcanic ashes and sand were showered down and spread by the waves +and currents so as to form strata of tuff, which are found +intercalated between beds of limestone and clay containing marine +shells, the thickness of the whole mass exceeding 2000 feet. The +fissures through which the lava rose may be seen in many places, +forming what are called <i>dikes.</i></p> + +<center><img src="../images1/fig133.jpg" width="336" height="321" alt= +"Fig. 133: Pecten jacobæus"></center> + +<p>No shell is more conspicuous in these Sicilian strata than the +great scallop, <i>Pecten jacobæus</i> (Fig. 133), now so +common in the neighbouring seas. The more we reflect on the +preponderating number of this and other recent shells, the more</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 207">[ 207 ]</a></p> + +<p>we are surprised at the great thickness, solidity, and height +above the sea of the rocky masses in which they are entombed, and +the vast amount of geographical change which has taken place since +their origin. It must be remembered that, before they began to +emerge, the uppermost strata of the whole must have been deposited +under water. In order, therefore, to form a just conception of +their antiquity, we must first examine singly the innumerable +minute parts of which the whole is made up, the successive beds of +shells, corals, volcanic ashes, conglomerates, and sheets of lava; +and we must afterwards contemplate the time required for the +gradual upheaval of the rocks, and the excavation of the valleys. +The historical period seems scarcely to form an appreciable unit in +this computation, for we find ancient Greek temples, like those of +Girgenti (Agrigentum), built of the modern limestone of which we +are speaking, and resting on a hill composed of the same; the site +having remained to all appearances unaltered since the Greeks first +colonised the island.</p> + +<p>It follows, from the modern geological date of these rocks, that +the fauna and flora of a large part of Sicily are of higher +antiquity than the country itself. The greater part of the island +has been raised above the sea since the epoch of existing species, +and the animals and plants now inhabiting it must have migrated +from adjacent countries, with whose productions the species are now +identical. The average duration of species would seem to be so +great that they are destined to outlive many important changes in +the configuration of the earth’s surface, and hence the necessity +for those innumerable contrivances by which they are enabled to +extend their range to new lands as they are formed, and to escape +from those which sink beneath the sea.</p> + +<p><b>Newer Pliocene Strata of the Upper Val D’arno.</b>—When +we ascend the Arno for about ten miles above Florence, we arrive at +a deep narrow valley called the Upper Val d’Arno, which appears +once to have been a lake, at a time when the valley below Florence +was an arm of the sea. The horizontal lacustrine strata of this +upper basin are twelve miles long and two broad. The depression +which they fill has been excavated out of Eocene and Cretaceous +rocks, which form everywhere the sides of the valley in highly +inclined stratification. The thickness of the more modern and +unconformable beds is about 750 feet, of which the upper 200 feet +consist of Newer Pliocene strata, while the lower are Older +Pliocene. The newer series are made up of sands and a conglomerate +called “sansino.” Among the imbedded fossil</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 208">[ 208 ]</a></p> + +<p>mammalia are <i>Mastodon arvernensis, Elephas meridionalis, +Rhinoceros etruscus, Hippopotamus major,</i> and remains of the +genera bear, hyæna, and felis, nearly all of which occur in +the Cromer forest-bed (see Chap. 13, p. 191).</p> + +<p>In the same upper strata are found, according to M. Gaudin, the +leaves and cones of <i>Glyptostrobus europæus</i>, a plant +closely allied to <i>G. heterophyllus</i>, now inhabiting the north +of China and Japan. This conifer had a wide range in time, having +been traced back to the Lower Miocene strata of Switzerland, and +being common at Œningen in the Upper Miocene, as we shall see +in the sequel <a href="ch14.html#page 218">(p. 218).</a></p> + +<p><b>Older Pliocene of Italy.—Subapennine +Strata.</b>—The Apennines, it is well-known, are composed +chiefly of Secondary or Mesozoic rocks, forming a chain which +branches off from the Ligurian Alps and passes down the middle of +the Italian peninsula. At the foot of these mountains, on the side +both of the Adriatic and the Mediterranean, are found a series of +tertiary strata, which form, for the most part, a line of low hills +occupying the space between the older chain and the sea. Brocchi +was the first Italian geologist who described this newer group in +detail, giving it the name of the Subapennine. Though chiefly +composed of Older Pliocene strata, it belongs, nevertheless, in +part, both to older and newer members of the tertiary series. The +strata, for example, of the Superga, near Turin, are Miocene; those +of Asti and Parma Older Pliocene, as is the blue marl of Sienna; +while the shells of the incumbent yellow sand of the same territory +approach more nearly to the recent fauna of the Mediterranean, and +may be Newer Pliocene.</p> + +<p>We have seen that most of the fossil shells of the Older +Pliocene strata of Suffolk which are of recent species are +identical with testacea now living in British seas, yet some of +them belong to Mediterranean species, and a few even of the genera +are those of warmer climates. We might therefore expect, in +studying the fossils of corresponding age in countries bordering +the Mediterranean, to find among them some species and genera of +warmer latitudes. Accordingly, in the marls belonging to this +period at Asti, Parma, Sienna, and parts of the Tuscan and Roman +territories, we observe the genera <i>Conus, Cypræa, +Strombus, Pyrula, Mitra, Fasciolaria, Sigaretus, Delphinula, +Ancillaria, Oliva, Terebellum, Terebra, Perna, Plicatula,</i> and +<i>Corbis</i>, some characteristic of tropical seas, others +represented by species more numerous or of larger size than those +now proper to the Mediterranean.</p> + +<p><b>Older Pliocene Flora of Italy.</b>—I have already +alluded to the Newer Pliocene deposits of the Upper Val d’Arno +above</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 209">[ 209 ]</a></p> + +<p>Florence, and stated that below those sands and conglomerates, +containing the remains of the <i>Elephas meridionalis</i> and other +associated quadrupeds, lie an older horizontal and conformable +series of beds, which may be classed as Older Pliocene. They +consist of blue clays with some subordinate layers of lignite, and +exhibit a richer flora than the overlying Newer Pliocene beds, and +one receding farther from the existing vegetation of Europe. They +also comprise more species common to the antecedent Miocene period. +Among the genera of flowering plants, M. Gaudin enumerates pine, +oak, evergreen oak, plum, plane, alder, elm, fig, laurel, maple, +walnut, birch, buckthorn, hickory, sumach, sarsaparilla, sassafras, +cinnamon, Glyptostrobus, Taxodium, Sequoia, Persea, Oreodaphne +(Fig. 134), Cassia, and Psoralea, and some others. This assemblage +of plants indicates a warm climate, but not so subtropical an one +as that of the Upper Miocene period, which will presently be +considered.</p> + +<center><img src="../images1/fig134.jpg" width="421" height="320" alt= +"Fig. 134: Creodaphne Heerii. Fig. 135: Liquidambar europæum, var. trilobatum"> +</center> + +<p>M. Gaudin, jointly with the Marquis Strozzi, has thrown much +light on the botany of beds of the same age in another part of +Tuscany, at a place called Montajone, between the rivers Elsa and +Evola, where, among other plants, is found the <i>Oreodaphne +Heerii</i>, Gaud. (see Fig. 134), which is probably only a variety +of <i>Oreodaphne foetens</i>, or the laurel called</p> + +<p class="fnote">* Feuilles fossiles de la Toscane.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 210">[ 210 ]</a></p> + +<p>the Til in Madeira, where, as in the Canaries, it constitutes a +large portion of the native woods, but can not now endure the +climate of Europe. In the fossil specimens the same glands or +protuberances are preserved* (see Fig. 134) as those which are seen +in the axils of the primary veins of the leaves in the recent Til. +Another plant also indicating a warmer climate is the <i> +Liquidambar europæum</i>, Brong. (see Fig. 135), a species +nearly allied to <i>L. styracifluum</i>, L., which flourishes in +most places in the Southern States of North America, on the borders +of the Gulf of Mexico.</p> + +<p class="fnote">* Contributions à la Flore fossile +Italienne. Gaudin and Strozzi. Plate 11, Fig. 3. Gaudin, p. 22.</p> + +<br> +<hr> +<small><a href="contents.html">Contents</a> / <a href="ch12.html"> +Chapter XII</a> / <a href="ch14.html">Chapter XIV</a></small> +</body> +</html> + |