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diff --git a/old/3772-h/files/ch22.html b/old/3772-h/files/ch22.html new file mode 100644 index 0000000..1c57fe3 --- /dev/null +++ b/old/3772-h/files/ch22.html @@ -0,0 +1,458 @@ +<!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 385">[ 385 ]</a></p> + +<p> </p> + +<center> +<h3>SECONDARY OR MESOZOIC SERIES</h3> + +<hr width="40%"> +<br> +<br> +<b>Chapter XXII</b><br> +<br> +PERMIAN OR MAGNESIAN LIMESTONE GROUP.</center> + +<p class="intro">Line of Separation between Mesozoic and +Palæozoic Rocks. — Distinctness of Triassic and Permian +Fossils. — Term Permian. — Thickness of calcareous and +sedimentary Rocks in North of England. — Upper, Middle, and +Lower Permian. — Marine Shells and Corals of the English +Magnesian Limestone. — Reptiles and Fish of Permian +Marl-slate. — Foot-prints of Reptiles. — Angular +Breccias in Lower Permian. — Permian Rocks of the Continent. +— Zechstein and Rothliegendes of Thuringia. — Permian +Flora. — Its generic Affinity to the Carboniferous.</p> + +<p>In pursuing our examination of the strata in descending order, +we have next to pass from the base of the Secondary or Mesozoic to +the uppermost or newest of the Primary or Palæozoic +formations. As this point has been selected as a line of +demarkation for one of the three great divisions of the +fossiliferous series, the student might naturally expect that by +aid of lithological and palæontological characters he would +be able to recognise without difficulty a distinct break between +the newer and older group. But so far is this from being the case +in Great Britain, that nowhere have geologists found more +difficulty in drawing the line of separation than between the +Secondary and Primary series. The obscurity has arisen from the +great resemblance in colour and mineral character of the Triassic +and Permian red marls and sandstones, and the scarcity and often +total absence in them of organic remains. The thickness of the +strata belonging to each group amounts in some places to several +thousand feet; and by dint of a careful examination of their +geological position, and of those fossil, animal, and vegetable +forms which are occasionally met with in some members of each +series, it has at length been made clear that the older or Permian +rocks are more connected with the Primary or Palæozoic than +with the Secondary or Mesozoic strata already described.</p> + +<p>The term Permian has been proposed for this group by</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 386">[ 386 ]</a></p> + +<p>Sir R. Murchison, from Perm, a Russian province, where it +occupies an area twice the size of France, and contains a great +abundance and variety of fossils, both vertebrate and invertebrate. +Professor Sedgwick in 1832* described what is now recognised as the +central member of this group, the Magnesian limestone, showing that +it attained a thickness of 600 feet along the north-east of +England, in the counties of Durham, Yorkshire, and Nottinghamshire, +its lower part often passing into a fossiliferous marl-slate and +resting on an inferior Red Sandstone, the equivalent of the +Rothliegendes of Germany. It has since been shown that some of the +Red Sandstones of newer date also belong to the Permian group; and +it appears from the observations of Mr. Binney, Sir R. Murchison, +Mr. Harkness, and others, that it is in the region where the +limestone is most largely developed, as, for example, in the county +of Durham, that the associated red sandstones or sedimentary rocks +are thinnest, whereas in the country where the latter are thickest +the calcareous member is reduced to thirty, or even sometimes to +ten feet. It is clear, therefore, says Mr. Hull, that the +sedimentary region in the north of England area has been to the +westward, and the calcareous area to the eastward; and that in this +group there has been a development from opposite directions of the +two types of strata.</p> + +<p>In illustration of this he has given us the following table:</p> + +<center><small>THICKNESS OF PERMIAN STRATA IN NORTH OF +ENGLAND.</small></center> + +<center> +<table border="0" cellspacing="4" cellpadding="0" summary= +"Upper, middle, and lower Permian in N.W. and N.E. of England." +width="80%"> +<tr> +<td> </td> +<td align="center"><small>N.W. of England</small></td> +<td align="center"><small>N.E. of England</small></td> +</tr> + +<tr> +<td></td> +<td align="center"><small>Feet</small></td> +<td align="center"><small>Feet</small></td> +</tr> + +<tr> +<td align="left">Upper Permian (Sedimentary)</td> +<td align="center">600</td> +<td align="center">50–100</td> +</tr> + +<tr> +<td align="left">Middle Permian (Calcareous)</td> +<td align="center">10–30</td> +<td align="center">600</td> +</tr> + +<tr> +<td align="left">Lower Permian (Sedimentary)</td> +<td align="center">3000</td> +<td align="center">100–250†</td> +</tr> +</table> +</center> + +<p><b>Upper Permian.</b>—What is called in this table the +Upper Permian will be seen to attain its chief thickness in the +north-west, or on the coast of Cumberland, as at St. Bee’s +Head, where it is described by Sir Roderick Murchison as consisting +of massive red sandstones with gypsum resting on a thin course of +Magnesian Limestone with fossils, which again is connected with the +Lower Red Sandstone, resembling the upper one in such a manner that +the whole forms a continuous series. No fossil footprints have been +found in this Upper as in the Lower Red Sandstone.</p> + +<p class="fnote">* Trans. Geol. Soc. Lond., Second Series, vol. +iii, p. 37.<br> +† Edward Hull, Ternary Classification, Quart. Journ. +Science, No. xxiii, 1869.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 387">[ 387 ]</a></p> + +<p><b>Middle Permian—Magnesian Limestone and +Marl-slate.</b>—This formation is seen upon the coast of +Durham and Yorkshire, between the Wear and the Tees. Among its +characteristic fossils are <i>Schizodus Schlotheimi</i> (Fig. 410) +and <i>Mytilus septifer</i> (Fig. 412). These shells occur at +Hartlepool and Sunderland, where the rock assumes an oolitic and +botryoidal character. Some of the beds in this division are +ripple-marked. In some parts of the coast of Durham, where the rock +is not crystalline, it contains as much as 44 per cent of carbonate +of magnesia, mixed with carbonate of lime. In other places—for it +is extremely variable in structure—it consists chiefly of +carbonate of lime, and has concreted into globular and +hemispherical masses, varying from the size of a marble to that of +a cannon-ball, and radiating from the centre. Occasionally earthy +and pulverulent beds pass into compact limestone or hard granular +dolomite. Sometimes the limestone appears in a brecciated form, the +fragments which are united together not consisting of foreign rocks +but seemingly composed of the breaking-up of the Permian limestone +itself, about the time of its consolidation. Some of the angular +masses in Tynemouth cliff are two feet in diameter.</p> + +<center><img src="../images3/fig410.jpg" width="439" height="153" alt= +"Fig. 410: Schidozus Schlotheimi, Permian crystalline limestone. Fig. 411: The hinge of Schizodus truncatus, Permian. Fig. 412: Mytilus septifer, Permian crystalline limestone."> +</center> + +<p>The magnesian limestone sometimes becomes very fossiliferous and +includes in it delicate bryozoa, one of which, <i>Fenestella +retiformis</i> (Fig. 413), is a very variable species, and has +received many different names. It sometimes attains a large size, +single specimens measuring eight inches in width. The same +bryozoan, with several other British species, is also found +abundantly in the Permian of Germany.</p> + +<p>The total known fauna of the Permian series of Great Britain at +present numbers 147 species, of which 77, or more than half, are +mollusca. Not one of these is common to rocks newer than the +Palæozoic, and the brachiopods are the only group which have +furnished species common to the more ancient or Carboniferous +rocks. Of these <i>Lingula Crednerii</i></p> + +<p> </p> + +<hr> +<p class="page"><a name="page 388">[ 388 ]</a></p> + +<p>(Fig. 415) is an example. There are 25 Gasteropods and only one +cephalopod, <i>Nautilus Freieslebeni,</i> which is also found in +the German Zechstein.</p> + +<center><img src="../images3/fig413.jpg" width="380" height="230" alt= +"Fig. 413: Magnesian Limestone.*"></center> + +<p>Shells of the genera <i>Productus</i> (Fig. 414) and <i> +Strophalosia</i> (the latter of allied form with hinge teeth), +which do not occur in strata newer than the Permian, are abundant +in the ordinary yellow magnesian limestone, as will be seen in the +valuable memoirs of Messrs. King and Howse. They are accompanied by +certain species of <i>Spirifera</i> (Fig. 416), <i>Lingula +Crednerii</i> (Fig. 415), and other brachiopoda of the true primary +or palæozoic type. Some of this same tribe of shells, such as +Camarophoria, allied to Rhynchonella, Spiriferina, and two species +of <i>Lingula,</i> are specifically the same as fossils of the +carboniferous rocks. <i>Avicula, Arca,</i> and <i>Schizodus</i> +(Fig. 410), and other lamellibranchiate bivalves, are abundant, but +spiral univalves are very rare.</p> + +<center><img src="../images3/fig414.jpg" width="399" height="169" alt= +"Fig. 414: Productus horridus. Fig. 415: Lingula Crednerii. Fig. 416: Spirifera alata."> +</center> + +<p>Beneath the limestone lies a formation termed the marl-stone, +which consists of hard calcareous shales, marl-slate, and +thin-bedded limestones. At East Thickley, in Durham, where</p> + +<p class="fnote">* King's Monograph, pl. 2.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 389">[ 389 ]</a></p> + +<p>it is thirty feet thick, this slate has yielded many fine +specimens of fossil fish—of the genera <i>Palæoniscus</i> +ten species, <i>Pygopterus</i> two species, <i>Coelacanthus</i> two +species, and <i>Platysomus</i> two species, which as genera are +common to the older Carboniferous formation, but the Permian +species are peculiar, and, for the most part, identical with those +found in the marl-slate or copper-slate of Thuringia.</p> + +<center><img src="../images3/fig417.jpg" width="366" height="322" alt= +"Fig. 417: Restored outline of a fish of the genus Palæoniscus. Fig. 418: Shark, Heterocercal. Fig. 419: Shad. (Clupea. Herring tribe.) Homocereal."> +</center> + +<p>The <i>Palæoniscus</i> above mentioned belongs to that +division of fishes which M. Agassiz has called +“Heterocercal,” which have their tails unequally +bilobate, like the recent shark and sturgeon, and the vertebral +column running along the upper caudal lobe. (See Fig. 418.) The +“Homocercal” fish, which comprise almost all the 9000 +species at present known in the living creation, have the tail-fin +either single or equally divided; and the vertebral column stops +short, and is not prolonged into either lobe. (See Fig. 419.) Now +it is a singular fact, first pointed out by Agassiz, that the +heterocercal form, which is confined to a small number of genera in +the existing creation, is universal in the magnesian limestone, and +all the more ancient formations. It characterises the earlier +periods of the earth’s history, whereas in the secondary +strata, or those newer than the Permian, the homocercal tail +predominates.</p> + +<p>A full description has been given by Sir Philip Egerton of the +species of fish characteristic of the marl-slate, in Professor +King’s monograph before referred to, where figures of the</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 390">[ 390 ]</a></p> + +<p>ichthyolites, which are very entire and well preserved, will be +found. Even a single scale is usually so characteristically marked +as to indicate the genus, and sometimes even the particular +species. They are often scattered through the beds singly, and may +be useful to a geologist in determining the age of the rock.</p> + +<center><img src="../images3/fig420.jpg" width="429" height="356" alt= +"Fig. 420: Palæoniscus comptus. Fig. 421: Palæoniscus elegans. Fig. 422: Palæoniscus glaphyrus. Fig. 423: Cœlacanthus granulatus. Fig. 424: Pygopterus mandibularis. Fig. 425: Acrolepis Sedgwickii."> +</center> + +<p>We are indebted to Messrs. Hancock and Howse for the discovery +in this marl-slate at Midderidge, Durham, of two species of <i> +Protosaurus,</i> a genus of reptiles, one representative of which, +<i>P. Speneri,</i> has been celebrated ever since the year 1810 as +characteristic of the Kupfer-schiefer or Permian of Thuringia. +Professor Huxley informs us that the agreement of the Durham fossil +with Hermann von Meyer’s figure of the German specimen is +most striking. Although the head is wanting in all the examples yet +found, they clearly belong to the Lacertian order, and are +therefore of a higher grade than any other vertebrate animal +hitherto found fossil in a Palæozoic rock. Remains of +Labyrinthodont reptiles have also been met with in the same slate +near Durham.</p> + +<p><b>Lower Permian.</b>—The inferior sandstones which lie +beneath the marl-slate consist of sandstone and sand, separating +the Magnesian Limestone from the coal, in Yorkshire and Durham. In +some instances, red marl and gypsum have been found associated with +these beds. They have been classed</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 391">[ 391 ]</a></p> + +<p>with the Magnesian Limestone by Professor Sedgwick, as being +nearly co-extensive with it in geographical range, though their +relations are very obscure. But the principal development of Lower +Permian is, as we have seen by Mr. Hull’s table <a href= +"#page 386">p. 386</a>, in the northwest, where the Penrith +sandstone, as it has been called, and the associated breccias and +purple shales are estimated by Professor Harkness to attain a +thickness of 3000 feet. Organic remains are generally wanting, but +the leaves and wood of coniferous plants, and in one case a cone, +have been found. Also in the purple marls of Corncockle Muir near +Dumfries, very distinct footprints of reptiles occur, originally +referred to the Trias, but shown by Mr. Binney in 1856 to be +Permian. No bones of the animals which they represent have yet been +discovered.</p> + +<p><i>Angular Breccias in Lower Permian.</i>—A striking +feature in these beds is the occasional occurrence, especially at +the base of the formation, of angular and sometimes rounded +fragments of Carboniferous and older rocks of the adjoining +districts being included in a paste of red marl. Some of the +angular masses are of huge size.</p> + +<p>In the central and southern counties, where the Middle Permian +or Magnesian Limestone is wanting, it is difficult to separate the +upper and lower sandstones, and Mr. Hull is of opinion that the +patches of this formation found here and there in Worcestershire, +Shropshire, and other counties may have been deposited in a sea +separated from the northern basin by a barrier of Carboniferous +rocks running east and west, and now concealed under the Triassic +strata of Cheshire. Similar breccias to those before described are +found in the more southern counties last mentioned, where their +appearance is rendered more striking by the marked contrast they +present to the beds of well-rolled and rounded pebbles of the Trias +occupying a large area in the same region.</p> + +<p>Professor Ramsay refers the angular form and large size of the +fragments composing these breccias to the action of floating ice in +the sea. These masses of angular rock, some of them weighing more +than half a ton, and lying confusedly in a red, unstratified marl, +like stones in boulder-drift, are in some cases polished, striated, +and furrowed like erratic blocks in the moraine of a glacier. They +can be shown in some cases to have travelled from the parent rocks, +thirty or more miles distant, and yet not to have lost their +angular shape.*</p> + +<p><b>Permian Rocks of the Continent.</b>—Germany is the +classic ground of the Magnesian Limestone now called Permian.</p> + +<p class="fnote">* Ramsay, Quart. Geol. Journ., 1855; and Lyell, +Principles of Geology, vol. i, p. 223, 10th edit.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 392">[ 392 ]</a></p> + +<p>The formation was well studied by the miners of that country a +century ago as containing a thin band of dark-coloured cupriferous +shale, characterised at Mansfield in Thuringia by numerous fossil +fish. Beneath some variegated sandstones (not belonging to the +Trias, though often confounded with it) they came down first upon a +dolomitic limestone corresponding to the upper part of our Middle +Permian, and then upon a marl-slate richly impregnated with copper +pyrites, and containing fish and reptiles (Protosaurus) identical +in species with those of the corresponding marl-slate of Durham. To +the limestone they gave the name of Zechstein, and to the +marl-slate that of Mergel-schiefer or Kupfer-schiefer. Beneath the +fossiliferous group lies the Rothliegendes or Rothtodt-liegendes, +meaning the red-lyer or red-dead-lyer, so-called by the German +miners from its colour, and because the copper had <i>died out</i> +when they reached this underlying non-metalliferous member of the +series. This red under-lyer is, in fact, a great deposit of red +sandstone, breccia, and conglomerate with associated porphyry, +basalt, and amygdaloid.</p> + +<p>According to Sir R. Murchison, the Permian rocks are composed, +in Russia, of white limestone, with gypsum and white salt; and of +red and green grits, occasionally with copper ore; also magnesian +limestones, marl-stones, and conglomerates.</p> + +<center><img src="../images3/fig426.jpg" width="421" height="245" alt= +"Fig. 426: Walchia piniformis."></center> + +<p><b>Permian Flora.</b>—About 18 or 20 species of plants are +known in the Permian rocks of England. None of them pass down into +the Carboniferous series, but several genera, such as <i> +Alethopteris, Neuropteris, Walchia,</i> and <i>Ullmania,</i> are +common to the two groups. The Permian flora on the Continent +appears, from the researches of MM. Murchison and de Verneuil</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 393">[ 393 ]</a></p> + +<p>in Russia, and of MM. Geinitz and von Gutbier in Saxony, to be, +with a few exceptions, distinct from that of the coal.</p> + +<img src="../images3/fig427.jpg" width="87" height="145" alt= +"Fig. 27: Cardiocarpon Ottonis." align="left"> + +<p>In the Permian rocks of Saxony no less than 60 species of fossil +plants have been met with. Two or three of these, as <i>Calamites +gigas, Sphenopteris erosa,</i> and <i>S. lobata,</i> are also met +with in the government of Perm in Russia. Seven others, and among +them <i>Neuropteris Loshii, Pecopteris arborescens,</i> and <i>P. +similis,</i> and several species of <i>Walchia</i> (see Fig. 426), +a genus of Conifers, called <i>Lycopodites</i> by some authors, are +said by Geinitz to be common to the coal-measures.</p> + +<img src="../images3/fig428.jpg" width="134" height="336" alt= +"Fig. 428: Noeggerathia cuneifolia." align="right"> + +<p>Among the genera also enumerated by Colonel Gutbier are the +fruit called <i>Cardiocarpon</i> (see Fig. 427), <i> +Asterophyllites,</i> and Annularia, so characteristic of the +Carboniferous period; also <i>Lepidodendron,</i> which is common to +the Permian of Saxony, Thuringia, and Russia, although not +abundant. <i>Neoggerathia</i> (see Fig. 428), the leaves of which +have parallel veins without a midrib, and to which various generic +synonyms, such as <i>Cordaites, Flabellaria,</i> and <i> +Poacites,</i> have been given, is another link between the Permian +and Carboniferous vegetation. Coniferæ, of the Araucarian +division, also occur; but these are likewise met with both in older +and newer rocks. The plants called <i>Sigillaria</i> and <i> +Stigmaria,</i> so marked a feature in the Carboniferous period, are +as yet wanting in the true Permian.</p> + +<p>Among the remarkable fossils of the Rothliegendes, or lowest +part of the Permian in Saxony and Bohemia, are the silicified +trunks of tree-ferns called generically <i>Psaronius.</i> Their +bark was surrounded by a dense mass of air-roots, which often +constituted a great addition to the original stem, so as to double +or quadruple its diameter. The same remark holds good in regard to +certain living extra-tropical arborescent ferns, particularly those +of New Zealand.</p> + +<p>Upon the whole, it is evident that the Permian plants approach +much nearer to the Carboniferous flora than to the Triassic; and +the same may be said of the Permian fauna.</p> + +<p class="fnote">* Murchison's Russia, vol. ii, pl. A, fig. 3.</p> + +<br> +<hr> +<small><a href="contents.html">Contents</a> / <a href="ch21.html"> +Chapter XXI</a> / <a href="ch23.html">Chapter XXIII</a></small> +</body> +</html> + |