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diff --git a/old/3772-h/files/ch24.html b/old/3772-h/files/ch24.html new file mode 100644 index 0000000..82f7c05 --- /dev/null +++ b/old/3772-h/files/ch24.html @@ -0,0 +1,810 @@ +<!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 420">[ 420 ]</a></p> + +<p> </p> + +<center><b>Chapter XXIV</b><br> +<br> +FLORA AND FAUNA OF THE CARBONIFEROUS PERIOD.</center> + +<p class="intro">Vegetation of the Coal Period. — Ferns, +Lycopodiaceæ, Equisetaceæ, Sigillariæ, +Stigmariæ, Coniferæ. — Angiosperms. — +Climate of the Coal Period. — Mountain Limestone. — +Marine Fauna of the Carboniferous Period. — Corals. — +Bryozoa, Crinoidea. — Mollusca. — Great Number of +fossil Fish. — Foraminifera.</p> + +<p><b>Vegetation of the Coal Period.</b>—In the last chapter +we have seen that the seams of coal, whether bituminous or +anthracitic, are derived from the same species of plants, and +Goppert has ascertained that the remains of every family of plants +scattered through the shales and sandstones of the coal-measures +are sometimes met with in the pure coal itself—a fact which adds +greatly to the geological interest of this flora.</p> + +<p>The coal-period was called by Adolphe Brongniart the age of +Acrogens,* so great appears to have been the numerical +preponderance of flowerless or cryptogamic plants of the families +of ferns, club-mosses, and horse-tails. He reckoned the known +species in 1849 at 500, and the number has been largely increased +by recent research in spite of reductions owing to the discovery +that different parts of even the same plants had been taken for +distinct species. Notwithstanding these changes, Brongniart’s +generalisation concerning this flora still holds true, namely, that +the state of the vegetable world was then extremely different from +that now prevailing, not only because the cryptogamous plants +constituted nearly the whole flora, but also because they were, on +the whole, more highly developed than any belonging to the same +class now existing, and united some forms of structure now only +found separately and in distinct orders. The only phænogamous +plants were constitute any feature in the coal are the +coniferæ; monocotyledonous angiosperms appear to have been +very rare, and the dicotyledonous, with one or two doubtful +exceptions, were wanting. For this we are in some measure prepared +by what we have seen of the Secondary or Mesozoic floras if, +consistently with the belief in the theory of evolution, we expect +to find the prevalence of simpler and less specialised organisms in +older rocks.</p> + +<p class="fnote">* For botanical nomenclature see <a href= +"ch17.html#page 304">p. 304</a>.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 421">[ 421 ]</a></p> + +<p><b>Ferns.</b>—We are struck at the first glance with the +similarity of the ferns to those now living. In the fossil genus +<i>Pecopteris,</i> for example (Fig. 448), it is not easy to decide +whether the fossils might not be referred to the same genera as +those established for living ferns; whereas, in regard to some of +the other contemporary families of plants, with the exception of +the fir tribe, it is not easy to guess even the class to which they +belong. The ferns of the Carboniferous period are generally without +organs of fructification, but in the few instances in which these +do occur in a fit state for microscopical investigations they agree +with those of the living ferns.</p> + +<center><img src="../images3/fig448.jpg" width="386" height="291" alt= +"Fig. 448: Pecopteris elliptica. Fig. 449: Caulopteris primæva."> +</center> + +<p>When collecting fossil specimens from the coal-measures of +Frostburg, in Maryland, I found in the iron-shales several species +with well-preserved rounded spots or marks of the sori (see Fig. +448). In the general absence of such characters they have been +divided into genera distinguished chiefly by the branching of the +fronds and the way in which the veins of the leaves are disposed. +The larger portion are supposed to have been of the size of +ordinary European ferns, but some were decidedly arborescent, +especially the group called <i>Caulopteris</i> (see Fig. 449) by +Lindley, and the <i>Psaronius</i> of the upper or newest +coal-measures, before alluded to (<a href="ch22.html#page 393">p. +393</a>). All the recent tree-ferns belong to one tribe +(<i>Polypodiaceæ</i>), and to a small number only of genera +in that tribe, in which the surface of the trunk is marked with +scars,</p> + +<p class="fnote">* Sir C. Bunbury, Quart. Geol. Journ., vol. ii, +1845.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 422">[ 422 ]</a></p> + +<p>or cicatrices, left after the fall of the fronds. These scars +resemble those of <i>Caulopteris.</i></p> + +<p>No less than 130 species of ferns are enumerated as having been +obtained from the British coal-strata, and this number is more than +doubled if we include the Continental and American species. Even if +we make some reduction on the ground of varieties which have been +mistaken, in the absence of their fructification, for species, +still the result is singular, because the whole of Europe affords +at present no more than sixty-seven indigenous species.</p> + +<center><img src="../images3/fig450.jpg" width="315" height="346" alt= +"Living tree-ferns of different genera. Fig. 450: Tree-fern from Isle of Bourbon. Fig. 451: Cyathea glauca, Mauritius. Fig. 452: Tree-fern from Brazil."> +</center> + +<p><b> +Lycopodiaceæ</b>—<i>Lepidodendron.</i>—About +forty species of fossil plants of the Coal have been referred to +this genus, more than half of which are found in the British +coal-measures. They consist of cylindrical stems or trunks, covered +with leaf-scars. In their mode of branching, they are always +dichotomous (see <a href="../images3/fig453.jpg">Fig. 454</a>). They +belong to the <i>Lycopodiaceæ,</i> bearing sporangia and +spores similar to those of the living representatives of this +family (<a href="../images3/fig457.jpg">Fig. 457</a>); and although +most of the Carboniferous species grew to the size of large trees, +Mr. Carruthers has found by careful measurement that the volume of +the fossil spores did not exceed that of the recent club-moss, a +fact of some geological importance, as it may help to explain the +facility with which these seeds may</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 423">[ 423 ]</a></p> + +<p>have been transported by the wind, causing the same wide +distribution of the species of the fossil forests in Europe and +America which we now observe in the geographical distribution of so +many living families of cryptogamous plants.</p> + +<center><img src="../images3/fig453.jpg" width="344" height="310" alt= +"Lepidodendrum Sternbergii. Coal-measures, near Newcastle. Fig. 453: Branching trunk, 49 feet long, supposed to have belonged to L. Sternbergii. Fig. 454: Branching stem with bark and leaves of L. Sternbergii. Fig. 455: Portion of same, nearer the root."> +</center> + +<img src="../images3/fig456.jpg" width="293" height="244" alt= +"Fig. 456: a. Lycopodium densum. Living species, New Zealand; b. Branch; c. Part of same, magnified." + align="right"> + +<p>The Figs. 453–455 represent a fossil <i>Lepidodendron,</i> +49 feet long, found in Jarrow Colliery, near Newcastle, lying in +shale parallel to the planes of stratification. Fragments of +others, found in the same shale, indicate, by the size of the +rhomboidal scars which cover them, a still greater magnitude.</p> + +<p>The living club-mosses, of which there are about 200 species, +are most abundant in tropical climates. They usually creep on the +ground, but some stand erect, as the <i>Lycopodium densum</i> from +New Zealand (see Fig. 456), which attains a height of three +feet.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 424">[ 424 ]</a></p> + +<center><img src="../images3/fig457.jpg" width="421" height="161" alt= +"Fig. 457: a. Lepidostrobus ornatus; b. Portion of a section, showing the large sporangia in their natural position, and each supported by its bract or scale; c. Spores in these sporangia, highly magnified."> +</center> + +<p>In the Carboniferous strata of Coalbrook Dale, and in many other +coal-fields, elongated cylindrical bodies, called fossil cones, +named <i>Lepidostrobus</i> by M. Adolphe Brongniart, are met with. +(See Fig. 457.) They often form the nucleus of concretionary balls +of clay-ironstone, and are well preserved, exhibiting a conical +axis, around which a great quantity of scales were compactly +imbricated. The opinion of M. Brongniart that the <i> +Lepidostrobus</i> is the fruit of <i>Lepidodendron</i> has been +confirmed, for these <i>strobili</i> or fruits have been found +terminating the tip of a branch of a well-characterised <i> +Lepidodendron</i> in Coalbrook Dale and elsewhere.</p> + +<center><img src="../images3/fig458.jpg" width="369" height="262" alt= +"Fig. 458: Calamites Sucowii, common throughout Europe. Fig. 459: Stem of Fig. 458, as retored by Dr. Dawson."> +</center> + +<p><b>Equisetaceæ.</b>—To this family belong two fossil +genera of the coal, <i>Equisetites</i> and <i>Calamites.</i> The +Calamites were evidently closely related to the modern horse-tails +(Equiseta) differing principally in their great size, the want of +sheaths at the joints, and some details of fructification. They +grew in dense brakes on sandy and muddy flats in the manner of +modern Equisetaceæ, and their remains are frequent in the</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 425">[ 425 ]</a></p> + +<p>coal. Seven species of this plant occur in the great Nova Scotia +section before described, where the stems of some of them five +inches in diameter, and sometimes eight feet high, may be seen +terminating downward in a tapering root (see Fig. 460).</p> + +<center><img src="../images3/fig460.jpg" width="408" height="233" alt= +"Fig. 460: Radical termination of a Calamite. Fig. 461: Asterophyllites foliosus, Coal-measures, Newcastle."> +</center> + +<p>Botanists are not yet agreed whether the <i>Asterophyllites,</i> +a species of which is represented in Fig. 461, can form a separate +genus from the Calamite, from which, however, according to Dr. +Dawson, its foliage is distinguished by a true mid-rib, which is +wanting in the leaves known to belong to some Calamites.</p> + +<img src="../images3/fig462.jpg" width="95" height="176" alt= +"Fig. 462: Annularia sphenophylloides." align="left"><img src= +"../images3/fig463.jpg" width="92" height="166" alt= +"Fig. 463: Sphenophyllum erosum." align="right"> + +<p>Figs. 462 and 463 represent leaves of <i>Annularia</i> and <i> +Sphenophyllum,</i> common in the coal, and believed by Mr. +Carruthers to be leaves of Calamites. Dr. Williamson, who has +carefully studied the Calamites, thinks that they had a fistular +pith, exogenous woody stem, and thick smooth bark, which last +having always disappeared, leaves a fluted stem, as represented in +Fig. 459.</p> + +<p><b>Sigillaria.</b>—A large portion of the trees of the +Carboniferous period belonged to this genus, of which as many as 28 +species are enumerated as British. The structure, both internal and +external, was very peculiar, and, with reference to existing types, +very anomalous. They were formerly referred, by M. Ad. Brongniart, +to ferns, which they resemble in the scalariform texture of their +vessels and, in</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 426">[ 426 ]</a></p> + +<img src="../images3/fig464.jpg" width="158" height="275" alt= +"Fig. 464: Sigillaria lævigata." align="left"> + +<p>some degree, in the form of the cicatrices left by the base of +the leaf-stalks which have fallen off (see Fig. 464). But some of +them are ascertained to have had long linear leaves, quite unlike +those of ferns. They grew to a great height, from 30 to 60, or even +70 feet, with regular cylindrical stems, and without branches, +although some species were dichotomous towards the top. Their +fluted trunks, from one to five feet in diameter, appear to have +decayed more rapidly in the interior than externally, so that they +became hollow when standing; and when thrown prostrate, they were +squeezed down and flattened. Hence, we find the bark of the two +opposite sides (now converted into bright shining coal) constitute +two horizontal layers, one upon the other, half an inch, or an +inch, in their united thickness. These same trunks, when they are +placed obliquely or vertically to the planes of stratification, +retain their original rounded form, and are uncompressed, the +cylinder of bark having been filled with sand, which now affords a +cast of the interior.</p> + +<p>Dr. Hooker inclined to the belief that the <i> +Sigillariæ</i> may have been cryptogamous, though more highly +developed than any flowerless plants now living. Dr. Dawson having +found in some species what he regards as medullary rays, thinks +with Brongniart that they have some relation to gymnogens, while +Mr. Carruthers leans to the opinion that they belong to the +Lycopodiaceæ.</p> + +<p><i>Stigmaria.</i>—This fossil, the importance of which has +already been pointed out in <a href="ch23.html#page 398">p. +398</a>, was originally conjectured to be an aquatic plant. It is +now ascertained to be the root of <i>Sigillaria.</i> The connection +of the roots with the stem, previously suspected, on botanical +grounds, by Brongniart, was first proved, by actual contact, in the +Lancashire coal-field, by Mr. Binney. The fact has lately been +shown, even more distinctly, by Mr. Richard Brown, in his +description of the <i>Stigmariæ</i> occurring in the +under-clays of the coal-seams of the Island of Cape Breton, in Nova +Scotia. In a specimen of one of these, represented in Fig. 465, the +spread of the roots was sixteen feet, and some of them sent out +rootlets, in all directions, into the surrounding clay.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 427">[ 427 ]</a></p> + +<center><img src="../images3/fig465.jpg" width="365" height="176" alt= +"Fig. 465: Stigmaria attached to a trunk of Sigillaria."></center> + +<p>In the sea-cliffs of the South Joggins in Nova Scotia, I +examined several erect <i>Sigillariæ,</i> in company with Dr. +Dawson, and we found that from the lower extremities of the trunk +they sent out <i>Stigmariæ</i> as roots. All the stools of +the fossil trees dug out by us divided into four parts, and these +again bifurcated, forming eight roots, which were also dichotomous +when traceable far enough. The cylindrical rootlets formerly +regarded as leaves are now shown by more perfect specimens to have +been attached to the root by fitting into deep cylindrical pits. In +the fossil there is rarely any trace of the form of these cavities, +in consequence of the shrinkage of the surrounding tissues. Where +the rootlets are removed, nothing remains on the surface of the +Stigmaria but rows of mammillated tubercles (see Figs. 466, 467), +which have formed the base of each rootlet.</p> + +<center><img src="../images3/fig466.jpg" width="440" height="202" alt= +"Fig. 466: Stigmaria ficoides. Fig. 467: Surface of another individual of same species, showing form of tubercles."> +</center> + +<p>These protuberances may possibly indicate the place of a joint +at the lower extremity of the rootlet. Rows of these tubercles are +arranged spirally round each root, which have always a medullary +axis and woody system much resembling that of <i>Sigillaria,</i> +the structure of the vessels being, like it, scalariform.</p> + +<p><b>Coniferæ.</b>—The coniferous trees of this period +are referred to five genera;</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 428">[ 428 ]</a></p> + +<img src="../images3/fig468.jpg" width="123" height="374" alt= +"Fig. 468: Fragment of coniferous wood." align="left"> + +<p>the woody structure of some of them showing that they were +allied to the Araucarian division of pines, more than to any of our +common European firs. Some of their trunks exceeded forty-four feet +in height. Many, if not all of them, seem to have differed from +living <i>Coniferæ</i> in having large piths; for Professor +Williamson has demonstrated the fossil of the coal-measures called +<i>Sternbergia</i> to be the pith of these trees, or rather the +cast of cavities formed by the shrinking or partial absorption of +the original medullary axis (see Figs. 468, 469). This peculiar +type of pith is observed in living plants of very different +families, such as the common Walnut and the White Jasmine, in which +the pith becomes so reduced as simply to form a thin lining of the +medullary cavity, across which transverse plates of pith extend +horizontally, so as to divide the cylindrical hollow into discoid +interspaces. When these interspaces have been filled up with +inorganic matter, they constitute an axis to which, before their +true nature was known, the provisional name of <i>Sternbergia</i> +(<i>d, d,</i> Fig. 468) was given. In the above specimen the +structure of the wood (<i>b,</i> Figs. 468 and 469) is coniferous, +and the fossil is referable to Endlicher’s fossil genus <i> +Dadoxylon.</i></p> + +<center><img src="../images3/fig469.jpg" width="317" height="162" alt= +"Fig. 469: Magnified portion of Fig. 468; transverse section."> +</center> + +<p>The fossil named <i>Trigonocarpon</i> (Figs. 470 and 471), +formerly supposed to be the fruit of a palm, may now, according to +Dr. Hooker, be referred, like the <i>Sternbergia,</i> to the <i> +Coniferæ.</i> Its geological importance is great, for so +abundant is it in the coal-measures, that in certain localities the +fruit of</p> + +<p class="fnote">* Manchester Phil. Mem., vol. ix, 1851.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 429">[ 429 ]</a></p> + +<img src="../images3/fig470.jpg" width="140" height="148" alt= +"Fig. 470: Trigonocarpum ovatum." align="right"><img src= +"../images3/fig471.jpg" width="103" height="231" alt= +"Fig. 471: Trigonocarpum olivæforme." align="left"> + +<p>some species may be procured by the bushel; nor is there any +part of the formation where they do not occur, except the +under-clays and limestone. The sandstone, ironstone, shales, and +coal itself, all contain them. Mr. Binney has at length found in +the clay-ironstone of Lancashire several specimens displaying +structure, and from these, says Dr. Hooker, we learn that the <i> +Trigonocarpon</i> belonged to that large section of existing +coniferous plants which bear fleshy solitary fruits, and not cones. +It resembled very closely the fruit of the Chinese genus <i> +Salisburia,</i> one of the Yew tribe, or Taxoid conifers.</p> + +<img src="../images3/fig472.jpg" width="107" height="229" alt= +"Fig. 472: Antholithes." align="right"> + +<p><b>Angiosperms.</b>—The curious fossils called <i> +Antholithes</i> by Lindley have usually been considered to be +flower spikes, having what seems a calyx and linear petals (see +Fig. 472). Dr. Hooker, after seeing very perfect specimens, also +thought that they resembled the spike of a highly-organised plant +in full flower, such as one of the <i>Bromeliaceæ,</i> to +which Professor Lindley had at first compared them. Mr. Carruthers, +who has lately examined a large series in different museums, +considers it to be a dicotyledonous angiosperm allied to <i> +Orobanche</i> (broom-rape), which grew, not on the soil, but +parasitically on the trees of the coal forests.</p> + +<p>In the coal-measures of Granton, near Edinburgh, a remarkable +fossil (Fig. 473) was found and described in 1840,* by Dr. Robert +Paterson. It was compressed between layers of bituminous shale, and +consists of a stem bearing a cylindrical spike, <i>a,</i> which in +the portion preserved in the slate exhibits two subdivisions and +part of a third. The spike is covered on the exposed surface with +the four-cleft calyces of the flowers arranged in parallel rows. +The stem shows, at <i>b,</i> a little below the spike, remains of a +lateral appendage, which is supposed to indicate the beginning of +the spathe. The fossil has been referred to the <i> +Aroidiæ,</i> and</p> + +<p class="fnote">* Trans. of Bot. Soc. of Edinburgh, vol. i, +1844.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 430">[ 430 ]</a></p> + +<img src="../images3/fig473.jpg" width="260" height="357" alt= +"Fig. 473: Pothocites Grantonii." align="left"> + +<p>there is every probability that it is a true member of this +order. There can at least be no doubt as to the high grade of its +organisation, and that it belongs to the monocotyledonous +angiosperms. Mr. Carruthers has carefully examined the original +specimen in the Botanical Museum, Edinburgh, and thinks it may have +been an epiphyte.</p> + +<p><b>Climate of the Coal Period.</b>—As to the climate of +the Coal, the Ferns and the Coniferæ are perhaps the two +classes of plants which may be most relied upon as leading us to +safe conclusions, as the genera are nearly allied to living types. +All botanists admit that the abundance of ferns implies a moist +atmosphere. But the coniferæ, says Hooker, are of more +doubtful import, as they are found in hot and dry, and in cold and +dry climates; in hot and moist, and in cold and moist regions. In +New Zealand the coniferæ attain their maximum in numbers, +constituting 1/62 part of all the flowering plants; whereas in a +wide district around the Cape of Good Hope they do not form 1/1600 +of the phenogamic flora. Besides the conifers, many species of +ferns flourish in New Zealand, some of them arborescent, together +with many lycopodiums; so that a forest in that country may make a +nearer approach to the carboniferous vegetation than any other now +existing on the globe.</p> + +<br> +<center><small>MARINE FAUNA OF THE +CARBONIFEROUS PERIOD.</small></center> + +<p>It has already been stated that the Carboniferous or Mountain +Limestone underlies the coal-measures in the South of England and +Wales, whereas in the North, and in Scotland, marine calcareous +rocks partly of the age of the Mountain Limestone alternate with +shales and sandstones, containing seams of coal. In its most +calcareous form the Mountain Limestone is destitute of land-plants, +and is loaded</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 431">[ 431 ]</a></p> + +<p>with marine remains—the greater part, indeed, of the rock being +made up bodily of crinoids, corals, and bryozoa with interspersed +mollusca.</p> + +<p><b>Corals.</b>—The corals deserve especial notice, as the +cup-and-star corals, which have the most massive and stony +skeletons, display peculiarities of structure by which they may be +distinguished generally, as MM. Milne Edwards and Haime first +pointed out, from all species found in strata newer than the +Permian. There is, in short, an ancient or <i>Palæozoic,</i> +and a modern or <i>Neozoic</i> type, if, by the latter term, we +designate (as proposed by Professor E. Forbes) all strata from the +triassic to the most modern, inclusive. The accompanying diagrams +(Figs. 474, 475) may illustrate these types.</p> + +<table border="0" cellspacing="0" cellpadding="0" bgcolor="white" +summary= +"Fig. 474: Polæozoic type of lamelliferous cup-shaped Coral. Fig. 475: Neozole type of lamelliferous cup-shaped Coral."> +<tr> +<td align="left" valign="top"><img src="../images3/fig474.jpg" width= +"162" height="226" alt= +"Fig. 474: Palæozoic type of lamelliferous cup-shaped Coral."> +</td> +<td align="left" valign="top"> +<ol class="tab"> +<li>Vertical section of <i>Campophyllum flexuosum,</i> +(<i>Cyathophyllum,</i> Goldfuss); from the Devonian of the Eifel. +The lamellæ are seen around the inside of the cup; the walls +consist of cellular tissue; and large transverse plates, called <i> +tubulæ,</i> divide the interior into chambers.</li> + +<li>Arrangement of the <i>lamellæ</i> in <i>Polycoelia +profunda,</i> Germar, sp.; from the Magnesian Limestone, Durham. +This diagram shows the quadripartite arrangement of the primary +septa, characteristic of palæozoic corals, there being four +principal and eight intermediate lamellæ, the whole number in +this type being always a multiple of four.</li> + +<li><i>Stauria astræiformis,</i> Milne Edwards. Young group, +natural size. Upper Silurian, Gothland. The lamellæ or septal +system in each cup are divided by four prominent ridges into four +groups.</li> +</ol> +</td> +</tr> + +<tr> +<td align="left" valign="top"><img src="../images3/fig475.jpg" width= +"162" height="204" alt= +"Fig. 475: Neozoic type of lamelliferous cup-shaped Coral."></td> +<td align="left" valign="top"> +<ol class="tab"> +<li><i>Parasmilia centralis,</i> Mantell, sp. Vertical section. +Upper Chalk, Gravesend. In this type the lamellæ are massive, +and extend to the axis or columella composed of loose cellular +tissue, without any transverse plates like those in Fig. 474, <i> +a.</i></li> + +<li><i>Cyathina Bowerbankii,</i> Ed. and H. Transverse section, +enlarged. Gault, Folkestone. In this coral the primary septa are a +multiple of six. The twelve principal plates reach the columella, +and between each pair there are three secondaries, in all +forty-eight. The short intermediate plates which proceed from the +columella are not counted. They are called <i>pali.</i></li> + +<li><i>Fungia patellaris,</i> Lamarck. Recent; very young state. +Diagram of its six primary and six secondary septa, magnified. The +sextuple arrangement is always more manifest in the young than in +the adult state.</li> +</ol> +</td> +</tr> +</table> + +<p> </p> + +<hr> +<p class="page"><a name="page 432">[ 432 ]</a></p> + +<p>It will be seen that the more ancient corals have what is called +a quadripartite arrangement of the chief plates or <i> +lamellæ</i>—parts of the skeleton which support the organs +of reproduction. The number of these lamellæ in the +Palæozoic type is 4, 8, 16, etc.; while in the Neozoic type +the number is 6, 12, 24, or some other multiple of six; and this +holds good, whether they be simple forms, as in Figs. 474, <i> +a,</i> and 475, <i>a,</i> or aggregate clusters of corallites, as +in 474, <i>c.</i> But further investigations have shown in this, as +in all similar grand generalisations in natural history, that there +are excepions to the rule. Thus in the Lower Greensand <i> +Holocystis elegans</i> (Ed. and H.) and other forms have the +Palæozoic type, and Dr. Duncan has shown to what extent the +Neozoic forms penetrate downward into the Carboniferous and +Devonian rocks.</p> + +<center><img src="../images3/fig476.jpg" width="396" height="313" alt= +"Fig. 476: Lithostrotion basaltiforme. Fig. 477: Lonsdaleia floriformis."> +</center> + +<p>From a great number of lamelliferous corals met with in the +Mountain Limestone, two species (Figs. 476, 477) have been +selected, as having a very wide range, extending from the eastern +borders of Russia to the British Isles, and being found almost +everywhere in each country. These fossils, together with numerous +species of <i>Zaphrentis, Amplexus, Cyathophyllum, Clisiophyllum, +Syringopora,</i> and <i>Michelinia,</i>* form a group of rugose +corals widely different from any that followed them.</p> + +<p class="fnote">* For figures of these corals, see +Palæontographical Society’s Monographs, 1852.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 433">[ 433 ]</a></p> + +<center><img src="../images3/fig478.jpg" width="381" height="254" alt= +"Fig. 478: Cyathocrinus planus. Fig. 479: Cyathocrinus caryocrinoides."> +</center> + +<p><b>Bryozoa and Crinoidea.</b>—Of the <i>Bryozoa,</i> the +prevailing forms are <i>Fenestella, Hemitrypa,</i> and <i> +Polypora,</i> and these often form considerable beds. Their +net-like fronds are easily recognised. <i>Crinoidea</i> are also +numerous in the Mountain Limestone (see Figs. 478, 479), two +genera, <i>Pentremites</i> and <i>Codonaster,</i> being peculiar to +this formation in Europe and North America.</p> + +<img src="../images3/fig480.jpg" width="166" height="146" alt= +"Fig. 480: Palæchinus gigas." align="right"> + +<p>In the greater part of them, the cup or pelvis, Figure 479, <i> +b,</i> is greatly developed in size in proportion to the arms, +although this is not the case in Fig. 478. The genera <i> +Poteriocrinus, Cyathocrinus, Pentremites, Actinocrinus,</i> and <i> +Platycrinus,</i> are all of them characteristic of this formation. +Other Echinoderms are rare, a few Sea-Urchins only being known: +these have a complex structure, with many more plates on their +surface than are seen in the modern genera of the same group. One +genus, the <i>Palæchinus</i> (Fig. 480), is the analogue of +the modern <i>Echinus,</i> but has four, five, or six rows of +plates in the interambulacral region or area, whereas the modern +genera have only two. The other, <i>Archæocidaris,</i> +represents, in like manner, the <i>Cidaris</i> of the present +seas.</p> + +<p><b>Mollusca.</b>—The British Carboniferous mollusca +enumerated by Mr. Etheridge* comprise 653 species referable to 86 +genera, occurring chiefly in the Mountain Limestone. Of</p> + +<p class="fnote">* Quart. Geol. Journ., vol. xxiii, p. 674, +1867.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 434">[ 434 ]</a></p> + +<center><img src="../images3/fig481.jpg" width="411" height="212" alt= +"Fig. 481: Productus semireticulatus. Fig. 482: Spirifera trigonalis."> +</center> + +<img src="../images3/fig483.jpg" width="134" height="147" alt= +"Fig. 483: Spirifera glabra." align="right"> + +<p>this large number only 40 species are common to the underlying +Devonian rocks, 9 of them being Cephalopods, 7 Gasteropods, and the +rest bivalves, chiefly Brachiopoda (or Palliobranchiates). This +latter group constitutes the larger part of the Carboniferous +Mollusca, 157 species being known in Great Britain alone, and it +will be found to increase in importance in the fauna of the primary +rocks the lower we descend in the series. Perhaps the most +characteristic shells of the formation are large species of <i> +Productus,</i> such as <i>P. giganteus, p. hemisphericus, P. +semireticulatus</i> (Fig. 481), and <i>P. scabriculus.</i> Large +plaited spirifers, as <i>Spirifera striata, S. rotundata,</i> and +<i>S. trigonalis</i> (Fig. 482), also abound; and smooth species, +such as <i>Spirifera glabra</i> (Fig. 483), with its numerous +varieties.</p> + +<center><img src="../images3/fig484.jpg" width="393" height="197" alt= +"Fig. 484: Terebratula hastata. Fig. 485: Aviculopecten sublobatus. Fig. 486: Pleurotomaria carinata."> +</center> + +<p>Among the brachiopoda, <i>Terebratula hastata</i> (Fig. 484) +deserves mention, not only for its wide range, but because it often +retains the pattern of the original coloured</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 435">[ 435 ]</a></p> + +<p>stripes which ornamented the living shell. These coloured bands +are also preserved in several lamellibranchiate bivalves, as in <i> +Aviculopecten</i> (Fig. 485), in which dark stripes alternate with +a light ground. In some also of the spiral univalves the pattern of +the original painting is distinctly retained, as in <i> +Pleurotomaria</i> (Fig. 486), which displays wavy blotches, +resembling the colouring in many recent trochidæ.</p> + +<center><img src="../images3/fig487.jpg" width="393" height="340" alt= +"Fig. 487: Euomphalus pentagulatus."></center> + +<p>Some few of the carboniferous mollusca, such as Avicula, <i> +Nucula</i> (sub-genus <i>Ctenodonta</i>), <i>Solemya,</i> and <i> +Lithodomus,</i> belong no doubt to existing genera; but the +majority, though often referred to as living types, such as <i> +Isocardia, Turritella,</i> and <i>Buccinum,</i> belong really to +forms which appear to have become extinct at the close of the +Palæozoic epoch. <i>Euomphalus</i> is a characteristic +univalve shell of this period. In the interior it is divided into +chambers (Fig. 487, <i>d</i>), the septa or partitions not being +perforated as in foraminiferous shells, or in those having +siphuncles, like the Nautilus. The animal appears to have retreated +at different periods of its growth from the internal cavity +previously formed, and to have closed all communication with it by +a septum. The number of chambers is irregular, and they are +generally wanting in the innermost whorl. The animal of the recent +<i>Turritella communis</i> partitions off in like manner as it +advances in age a part of its spire, forming a shelly septum.</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 436">[ 436 ]</a></p> + +<img src="../images3/fig488.jpg" width="139" height="146" alt= +"Fig. 488: Bellerophon costatus." align="left"> + +<p>More than twenty species of the genus <i>Bellerophon</i> (see +Fig. 488), a shell like the living Argonaut without chambers, occur +in the Mountain Limestone. The genus is not met with in strata of +later date. It is most generally regarded as belonging to the +pelagic Nucleobranchiata and the family Atlantidæ, partly +allied to the Glass-Shell, <i>Carinaria</i>; but by some few it is +thought to be a simple form of Cephalopod.</p> + +<img src="../images3/fig489.jpg" width="194" height="424" alt= +"Fig. 489: Portion of Orthoxeras laterale. Fig. 490: Goniatites crenistra." + align="right"> + +<p>The carboniferous Cephalopoda do not depart so widely from the +living type (the Nautilus) as do the more ancient Silurian +representatives of the same order; yet they offer some remarkable +forms. Among these is <i>Orthoceras,</i> a siphuncled and chambered +shell, like a Nautilus uncoiled and straightened (Fig. 489). Some +species of this genus are several feet long. The <i>Goniatite</i> +is another genus, nearly allied to the <i>Ammonite,</i> from which +it differs in having the lobes of the septa free from lateral +denticulations, or crenatures; so that the outline of these is +angular, continuous, and uninterrupted. The species represented in +Fig. 490 is found in most localities, and presents the zigzag +character of the septal lobes in perfection. The dorsal position of +the siphuncle, however, clearly distinguishes the Goniatite from +the Nautilus, and proves it to have belonged to the family of the +Ammonites, from which, indeed, some authors do not believe it to be +generically distinct.</p> + +<p><b>Fossil Fish.</b>—The distribution of these is +singularly partial; so much so, that M. De Koninck of Liége, +the eminent palæontologist, once stated to me that, in making +his extensive collection of the fossils of the Mountain Limestone +of Belgium, he had found no more than four or five examples of the +bones or teeth of fishes. Judging from Belgian data, he might have +concluded that this class of vertebrata was of extreme rarity in +the Carboniferous seas; whereas the</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 437">[ 437 ]</a></p> + +<img src="../images3/fig491.jpg" width="251" height="168" alt= +"Fig. 491: Psammodus porosus." align="left"> + +<p>investigation of other countries has led to quite a different +result. Thus, near Clifton, on the Avon, as well as at numerous +places around the Bristol basin from the Mendip Hills to Tortworth, +there is a celebrated “bone-bed,” almost entirely made +up of ichthyolites. It occurs at the base of the Lower Limestone +shales immediately resting upon the passage beds of the Old Red +Sandstone. Similar bone-beds occur in the Carboniferous Limestone +of Armagh, in Ireland, where they are made up chiefly of the teeth +of fishes of the Placoid order, nearly all of them rolled as if +drifted from a distance. Some teeth are sharp and pointed, as in +ordinary sharks, of which the genus <i>Cladodus</i> afford an +illustration; but the majority, as in <i>Psammodus</i> and <i> +Cochliodus,</i> are, like the teeth of the Cestracion of Port +Jackson (see <a href="../images2/fig261.jpg">Fig. 261</a>), massive +palatal teeth fitted for grinding. (See Figs. 491, 492.)</p> + +<img src="../images3/fig492.jpg" width="200" height="186" alt= +"Fig. 492: Cochliodus controtus." align="right"> + +<p>There are upward of seventy other species of fossil fish known +in the Mountain Limestone of the British Islands. The defensive +fin-bones of these creatures are not infrequent at Armagh and +Bristol; those known as <i>Oracanthus, Ctenocanthus,</i> and <i> +Onchus</i> are often of a very large size. Ganoid fish, such as <i> +Holoptychius,</i> also occur; but these are far less numerous. The +great <i>Megalichthys Hibberti</i> appears to range from the Upper +Coal-measures to the lowest Carboniferous strata.</p> + +<p><b>Foraminifera.</b>—In the upper part of the Mountain +Limestone group in the S.W. of England, near Bristol, limestones +having a distinct oolitic structure alternate with shales. In these +rocks the nucleus of every minute spherule is seen, under the +microscope, to consist of a small rhizopod or foraminifer. This +division of the lower animals, which is represented so fully at +later epochs by the Nummulites and their numerous minute allies, +appears in the Mountain Limestone to be restricted to a very few +species, among which <i>Textularia, Nodosaria, Endothyra,</i> and +<i>Fusulina</i> (Fig. 493), have been</p> + +<p> </p> + +<hr> +<p class="page"><a name="page 438">[ 438 ]</a></p> + +<img src="../images3/fig493.jpg" width="115" height="110" alt= +"Fig. 493: Fusulina cylindrica." align="left"> + +<p>recognised. The first two genera are common to this and all the +after periods; the third has been found in the Upper Silurian, but +is not known above the Carboniferous strata; the fourth (Fig. 493) +is characteristic of the Mountain Limestone in the United States, +Arctic America, Russia, and Asia Minor, but is also known in the +Permian.</p> + +<br> +<hr> +<small><a href="contents.html">Contents</a> / <a href="ch23.html"> +Chapter XXIII</a> / <a href="ch25.html">Chapter XXV</a></small> +</body> +</html> + |