The Ancient Life History of the Earth Part 13

From the Coal-measures of Nova Scotia. (After Dawson.)]

[Ill.u.s.tration: Fig. 125--_Haplophlebium Barnesi_, a Carboniferous insect, from the Coal-meastures of Nova Scotia. (After Dawson.)]

In addition to the water-inhabiting group of the Crustaceans, we find the articulate animals to be represented by members belonging to the air-breathing cla.s.ses of the _Arachnida, Myriapoda_, and _Insecta_. The remains of these, as might have been expected, are not known to occur in the marine limestones of the Carboniferous series, but are exclusively found in beds a.s.sociated with the Coal, which have been deposited in lagoons, estuaries, or marshes, in the immediate vicinity of the land, and which actually represent an old land-surface. The _Arachnids_ are at present the oldest known of their cla.s.s, and are represented both by true Spiders and Scorpions. Remains of the latter (fig. 123) have been found both in the Old and New Worlds, and indicate the existence in the Carboniferous period of Scorpions differing but very little from existing forms. The group of the _Myriapoda_, including the recent Centipedes and Galley-worms, is likewise represented in the Carboniferous strata, but by forms in many respects very unlike any that are known to exist at the present day. The most interesting of these were obtained by Princ.i.p.al Dawson, along with the bones of Amphibians and the sh.e.l.ls of Land-snails, in the sediment filling the hollow trunks of _Sigillaria_, and they belong to the genera _Xylobius_ (fig. 124) and Archiulus. Lastly, the true _insects_ are represented by various forms of Beetles (_Coleoptera_), _Orthoptera_ (such as c.o.c.kroaches), and _Neuropterous_ insects resembling those which we have seen to have existed towards the close of the Devonian period. One of the most remarkable of the latter is a huge May-fly (_Haplophlebium Barnesi_, fig. 125), with netted wings attaining an expanse of fully seven inches, and therefore much exceeding any existing Ephemerid in point of size.

[Ill.u.s.tration: Fig. 126.--Carboniferous _Polyzoa_. a, Fragment of _Polypora dendroides_, of the natural size, Ireland; a' Small portion of the same, enlarged to show the cells; b, Glauconome pulcherrima_, a fragment, of the natural size, Ireland; b', Portion of the same, enlarged; c, The central screw-like axis of _Archimedes Wortheni_, of the natural size--Carboniferous, America; c', Portion of the exterior of the frond of the same, enlarged; c'', Portion of the interior of the frond of the same showing the mouths of the cells, enlarged. (After M'Coy and Hall.)]

The lower groups of the _Mollusca_ are abundantly represented in the marine strata of the Carboniferous series by _Polyzoans_ and _Brachiopods_. Amongst the former, although a variety of other types are known, the majority still belong to the old group of the "Lace-corals" (_Fenestellidoe_), some of the characteristic forms of which are here figured (fig. 126). The graceful netted fronds of _Fenestella, Retepora_, and _Polypora_ (fig. 126, a) are highly characteristic, as are the slender toothed branches of _Glauconome_ (fig. 126, b). A more singular form, however, is the curious _Archimedes_ (fig. 126, c), which is so characteristic of the Carboniferous formation of North America.

In this remarkable type, the colony consists of a succession of funnel-shaped fronds, essentially similar to _Fenestella_ in their structure, springing in a continuous spiral from a strong screw-like vertical axis. The outside of the fronds is simply striated; but the branches exhibit on the interior the mouths of the little cells in which the semi-independent beings composing the colony originally lived.

[Ill.u.s.tration: Fig. 127.--Carboniferous _Braciopoda. a, _Producta semireticulata_, showing the slightly concave dorsal valve; a'

Side view of the same, showing the convex ventral valve; b, _Producta longispina_; c, _Orthis resupinata_; d, _Terebratula hastata_; e, _Athyris subtilita_; f, _Chonetes Hardrensis_; g, _Rhynchonella pleurodon_; h, _Spirifera trigonalis_. Most of these forms are widely distributed in the Carboniferous Limestone of Britain, Europe, America, &c. All the figures are of the natural size. (After Davidson, De Koninck, and Meek.)]

The _Brachiopods_ are extremely abundant, and for the most part belong to types which are exclusively or princ.i.p.ally Palaeozoic in their range. The old genera _Strophomena, Orthis_ (fig. 127, c), _Athyris_ (fig. 127, e), _Rhynchonella_ (fig. 127, g), and _Spirifera_ (fig. 127, h), are still well represented--the latter, in particular, existing under numerous specific forms, conspicuous by their abundance and sometimes by their size. Along with these ancient groups, we have representatives--for the first time in any plenty--of the great genus _Terebratula_ (fig. 127, d), which underwent a great expansion during later periods, and still exists at the present day. The most characteristic Carboniferous Brachiopods, however, belong to the family of the _Productidoe_, of which the princ.i.p.al genus is _Producta_ itself.

This family commenced its existence in the Upper Silurian with the genus _Chonetes_, distinguished by its spinose hinge-margin.

This genus lived through the Devonian, and flourished in the Carboniferous (fig. 127, f). The genus _Producta_ itself, represented in the Devonian by the nearly allied _Productella_, appeared first in the Carboniferous, at any rate, in force, and survived into the Permian; but no member of this extensive family has yet been shown to have over-lived the Palaeozoic period. The _Productoe_ of the Carboniferous are not only exceedingly abundant, but they have in many instances a most extensive geographical range, and some species attain what may fairly be considered-gigantic dimensions. The sh.e.l.l (fig. 127, a and b) is generally more or less semicircular, with a straight hinge-margin, and having its lateral angles produced into larger or smaller ears (hence its generic name--"_cochlea producta_"). One valve (the ventral) is usually strongly convex, whilst the other (the dorsal) is flat or concave, the surface of both being adorned with radiating ribs, and with hollow tubular spines, often of great length.

The valves are not locked together by teeth, and there is no sign in the fully-grown sh.e.l.l of an opening in or between the valves for the emission of a muscular stalk for the attachment of the sh.e.l.l to foreign objects. It is probable, therefore, that the _Productoe_, unlike the ordinary Lamp-sh.e.l.ls, lived an independent existence, their long spines apparently serving to anchor them firmly in the mud or ooze of the sea-bottom; but Mr Robert Etheridge, jun.; has recently shown that in one species the spines were actually employed as organs of adhesion, whereby the sh.e.l.l was permanently attached to some extraneous object, such as the stem of a Crinoid. The two species here figured are interesting for their extraordinarily extensive geographical range--_Producta semireticulata_ (fig. 127, a) being found in the Carboniferous rocks of Britain, the continent of Europe, Central Asia, China, India, Australia, Spitzbergen, and North and South America; whilst _P. Longispina_ (fig. 127, b) has a distribution little if at all less wide.

[Ill.u.s.tration: Fig. 128.--_Pupa (Dendropupa) vetusta_, a Carboniferous Land-snail from the Coal-measures of Nova Scotia.

a, The sh.e.l.l, of the natural size; b, The same, magnified; c, Apex of the sh.e.l.l, enlarged; d, Portion of the surface, enlarged. (After Dawson.)]

The higher _Mollusca_ are abundantly represented in the Carboniferous rocks by Bivalves (_Lamellibranchs_), Univalves (_Gasteropoda_), Winged-snails (_Pteropoda_), and _Cephalopods_. Amongst the Bivalves we may note the great abundance of Scallops (_Aviculopecten_ and other allied forms), together with numerous other types--some of ancient origin, others represented here for the first time. Amongst the Gasteropods, we find the characteristically Palaeozoic genera _Macrocheilus_ and _Loxonema_, the almost exclusively Palaeozoic _Euomphalus_, and the persistent, genus _Pleurotomaria_; whilst the free-swimming Univalves (_Heteropoda_)are represented by _Bellerophon_ and _Porcellia_, and the _Pteropoda_ by the old genus _Conularia_. With regard to the Carboniferous Univalves, it is also of interest to note here the first appearance of true air-breathing or terrestrial Molluscs, as discovered by Dawson and Bradley in the Coal-measures of Nova Scotia and Illinois. Some of these (_Conulus priscus_) are true Land-snails, resembling the existing _Zonites_; whilst others (_Pupa vetusta_, fig. 128) appear to be generically inseparable from the "Chrysalis-sh.e.l.ls" (_Pupa_) of the present day. All the known forms--three in number--are of small size, and appear to have been local in their distribution or in their preservation. More important, however, than any of the preceding, are the _Cephalopoda_, represented, as before, exclusively by the chambered sh.e.l.ls of the Tetrabranchiates.

The older and simpler type of these, with simple plain septa, and mostly a central siphuncle, is represented by the straight conical sh.e.l.ls of the ancient genus Orthoceras, and the bow-shaped sh.e.l.ls of the equally ancient _Cyrtoceras_--some of the former attaining a great size. The spirally-curved discoidal sh.e.l.ls of the persistent genus _Nautilus_ are also not unknown, and some of these likewise exhibit very considerable dimensions.

Lastly, the more complex family of the _Ammonitidoe_, with lobed or angulated septa, and a dorsally-placed siphuncle (situated on the convex side of the curved sh.e.l.ls), now for the first time commences to acquire a considerable prominence. The princ.i.p.al representative of this group is the genus _Goniat.i.tes_ (fig.

129), which commenced its existence in the Upper Silurian, is well represented in the Devonian, and attains its maximum here. In this genus, the sh.e.l.l is spirally curved, the septa are strongly lobed or angulated, though not elaborately frilled as in the Ammonites, and the siphuncle is dorsal. In addition to _Goniat.i.tes_, the sh.e.l.ls of true _Ammonites_, so characteristic of the Secondary period, have been described by Dr Waagen as occurring in the Carboniferous rocks of India.

[Ill.u.s.tration: Fig. 129.--_Goniat.i.tes (Aganides) Fossoe_.

Carboniferous Limestone.]

[Ill.u.s.tration: Fig. 130.--_Amblypterus macropterus_. Carboniferous.]

Coming finally to the _Vertebrata_, we have in the first place to very briefly consider the Carboniferous _fishes_. These are numerous; but, with the exception of the still dubious "Conodonts,"

belong wholly to the groups of the _Ganoids_ and the _Placoids_ (including under the former head remains which perhaps are truly referable to the group of the _Dipnoi_ or Mud-fishes). Amongst the _Ganoids_, the singular buckler-headed fishes of the Upper Silurian and Devonian (_Cephalaspidoe_) have apparently disappeared; and the princ.i.p.al types of the Carboniferous belong to the groups respectively represented at the present day by the Gar pike (_Lepidosteus_) of the North American lakes, and the _Polypterus_ of the rivers of Africa. Of the former, the genera _Paloeoniscus_ and _Amblypterus_ (fig. 130), with their small rhomboidal and enamelled scales, and their strongly unsymmetrical tails, are perhaps the most abundant. Of the latter, the most important are species belonging to the genera _Megalichthys_ and _Rhizodus_, comprising large fishes, with rhomboidal scales, unsymmetrical ("heterocercal") tails, and powerful conical teeth. These fishes are sometimes said to be "sauroid," from their presenting some Reptilian features in their organisation, and they must have been the scourges of the Carboniferous seas. The remains of _Placoid_ fishes in the Carboniferous strata are very numerous, but consist wholly of teeth and fin-spines, referable to forms more or less closely allied to our existing Port Jackson Sharks, Dog-fishes, and Rays. The teeth are of very various shapes and sizes,--some with sharp, cutting edges (_Petalodus, Cladodus_, &c.); others in the form of broad crushing plates, adapted, like the teeth of the existing Port Jackson Shark (_Cestracion Philippi_), for breaking down the hard sh.e.l.ls of Molluscs and Crustaceans. Amongst the many kinds of these latter, the teeth of _Psammodus_ and _Cochliodus_ (fig. 131) may be mentioned as specially characteristic. The fin-spines are mostly similar to those so common in the Devonian deposits, consisting of hollow defensive spines implanted in front of the pectoral or other fins, usually slightly curved, often superficially ribbed or sculptured, and not uncommonly serrated or toothed. The genera _Ctenacanthus, Gyracanthus, Homacanthus_, &c., have been founded for the reception of these defensive weapons, some of which indicate fishes of great size and predaceous habits.

[Ill.u.s.tration: Fig. 131.--Teeth of _Cochliodus contortus_.

Carboniferous Limestone, Britain.]

[Ill.u.s.tration: Fig. 132.--a, Upper surface of the skull of _Anthracosaurus Russelli_, one-sixth of the natural size: b, Part of one of the teeth cut across, and highly magnified to show the characteristic labyrinthine structure; c, One of the integumentary shields or scales, one-half of the natural size.

Coal-measures, Northumberland. (After Atthey.)]

In the Devonian rocks we meet with no other remains of Vertebrated animals save fishes only; but the Carboniferous deposits have yielded remains of the higher group of the _Amphibians_. This cla.s.s, comprising our existing Frogs, Toads, and Newts, stands to some extent in a position midway between the cla.s.s of the fishes and that of the true reptiles, being distinguished from the latter by the fact that its members invariably possess gills in their early condition, if not throughout life; whilst they are separated from the former by always possessing true lungs when adult, and by the fact that the limbs (when present at all) are never in the form of fins. The Amphibians, therefore, are all water-breathers when young, and have respiratory organs adapted for an aquatic mode of life; whereas, when grown up, they develop lungs, and with these the capacity for breathing air directly. Some of them, like the Frogs and Newts, lose their gills altogether on attaining the adult condition; but others, such as the living _Proteus_ and _Men.o.branchus_, retain their gills even after acquiring their lungs, and are thus fitted indifferently for an aquatic or terrestrial existence. The name of "Amphibia," though applied to the whole cla.s.s, is thus not precisely appropriate except to these last-mentioned forms (Gr. _amphi_, both; _bios_, life). The Amphibians also differ amongst themselves according as to whether they keep permanently the long tail which they all possess when young (as do the Newts and Salamanders), or lose this appendage when grown up (as do the Frogs and Toads). Most of them have naked skins, but a few living and many extinct forms have hard structures in the shape of scales developed in the integument.

All of them have well-ossified skeletons, though some fossil types are partially deficient in this respect; and all of them which possess limbs at all have these appendages supported by bones essentially similar to those found in the limbs of the higher Vertebrates. All the Carboniferous Amphibians belong to a group which has now wholly pa.s.sed away--namely, that of the _Labyrinthodonts_. In the marine strata which form the base of the Carboniferous series these creatures have only been recognised by their curious hand-shaped footprints, similar in character to those which occur in the Tria.s.sic rocks, and which will be subsequently spoken of under the name of _Cheirotherium_.

In the Coal-measures of Britain, the continent of Europe, and North America, however, many bones of these animals have been found, and we are now tolerably well acquainted with a considerable number of forms. All of them seem to have belonged to the division of Amphibians in which the long tail of the young is permanently retained; and there is evidence that some of them kept the gills also throughout life. The skull is of the characteristic Amphibian type (fig. 132, a), with two occipital condyles, and having its surface singularly pitted and sculptured; and the vertebrae are hollowed out at both ends. The lower surface of the body was defended by an armour of singular integumentary shields or scales (fig. 132, c); and an extremely characteristic feature (from which the entire group derives its name) is, that the walls of the teeth are deeply folded, so as to give rise to an extraordinary "labyrinthine"

pattern when they are cut across (fig. 132, b). Many of the Carboniferous Labyrinthodonts are of no great size, some of them very small, but others attain comparatively gigantic dimensions, though all fall short in this respect of the huge examples of this group which occur in the Trias. One of the largest, and at the same time most characteristic, forms of the Carboniferous series, is the genus _Anthracosaurus_, the skull of which is here figured.

No remains of true Reptiles, Birds, or Quadrupeds have as yet been certainly detected in the Carboniferous deposits in any part of the world. It should, however, be mentioned, that Professor Marsh, one of the highest authorities on the subject, has described from the Coal-formation of Nova Scotia certain vertebrae which he believes to have belonged to a marine reptile (_Eosaurus Acadia.n.u.s_), allied to the great _Ichthyosauri_ of the Lias. Up to this time no confirmation of this determination has been obtained by the discovery of other and more unquestionable remains, and it therefore remains doubtful whether these bones of _Eosaurus_ may not really belong to large Labyrinthodonts.

LITERATURE.

The following list contains some of the more important of the original sources of information to which the student of Carboniferous rocks and fossils may refer:--

(1) 'Geology of Yorkshire,' vol. ii.; 'The Mountain Limestone District.' John Phillips.

(2) 'Siluria.' Sir Roderick Murchison.

(3) 'Memoirs of the Geological Survey of Great Britain and Ireland.'

(4) 'Geological Report on Londonderry,' &c. Portlock.

(5) 'Acadian Geology.' Dawson.

(6) 'Geology of Iowa,' vol. i. James Hall.

(7) 'Reports of the Geological Survey of Illinois' (Geology and Palaeontology). Meek, Worthen, &c.

(8) 'Reports of the Geological Survey of Ohio' (Geology and Palaeontology). Newberry, Cope, Meek, Hall, &c.

(9) 'Description des Animaux fossiles qui se trouvent dans le Terrain Carbonifere de la Belgique,' 1843; with subsequent monographs on the genera _Productus_ and _Chonetes_, on _Crinoids_, on _Corals_, &c. De Koninck.

(10) 'Synopsis of the Carboniferous Fossils of Ireland.' M'Coy.

(11) 'British Palaeozoic Fossils.' M'Coy.

(12) 'Figures of Characteristic British Fossils.' Baily.

(13) 'Catalogue of British Fossils.' Morris.

(14) 'Monograph of the Carboniferous Brachiopoda of Britain'

(Palaeontographical Society). Davidson.

(15) 'Monograph of the British Carboniferous Corals'

(Palaeontographical Society). Milne-Edwards and Haime.

(16) 'Monograph of the Carboniferous Bivalve Entomostraca of Britain' (Palaeontographical Society). Rupert Jones, Kirkby, and George S. Brady.

(17) 'Monograph of the Carboniferous Foraminifera of Britain'

(Palaeontographical Society). H. B. Brady.

(18) "On the Carboniferous Fossils of the West of Scotland"--'Trans.

Geol. Soc.,' of Glasgow, vol. iii., Supplement. Young and Armstrong.

(19) 'Poissons Fossiles.' Aga.s.siz.

(20) "Report on the Labyrinthodonts of the Coal-measures"--'British a.s.sociation Report,' 1873. L. C. Miall.

(21) 'Introduction to the Study of Palaeontological Botany.' John Hutton Balfour.

(22) 'Traite de Paleontologie Vegetale.' Schimper.

(23) 'Fossil Flora.' Lindley and Hutton.

(24) 'Histoire des Vegetaux Fossiles.' Brongniart.

(25) 'On Calamites and Calamodendron' (Monographs of the Palaeontographical Society). Binney.

(26) 'On the Structure of Fossil Plants found in the Carboniferous Strata' (Palaeontographical Society). Binney.

Also numerous memoirs by Huxley, Davidson, Martin Duncan, Professor Young, John Young, R. Etheridge, jun., Baily, Carruthers, Dawson, Binney, Williamson, Hooker, Jukes, Geikie, Rupert Jones, Salter, and many other British and foreign observers.

CHAPTER XIV.

THE PERMIAN PERIOD.

The Permian formation closes the long series of the Palaeozoic deposits, and may in some respects be considered as a kind of appendix to the Carboniferous system, to which it cannot be compared in importance, either as regards the actual bulk of its sediments or the interest and variety of its life-record. Consisting, as it does, largely of red rocks--sandstones and marls--for the most part singularly dest.i.tute of organic remains, the Permian rocks have been regarded as a lacustrine or fluviatile deposit; but the presence of well-developed limestones with indubitable marine remains entirely negatives this view. It is, however, not improbable that we are presented in the Permian formation, as known to us at present, with a series of sediments laid down in inland seas of great extent, due to the subsidence over large areas of the vast land-surfaces of the Coal-measures. This view, at any rate, would explain some of the more puzzling physical characters of the formation, and would not be definitely negatived by any of its fossils.

A large portion of the Permian series, as already remarked, consists of sandstones and marls, deeply reddened by peroxide of iron, and often accompanied by beds of gypsum or deposits of salt. In strata of this nature few or no fossils are found; but their shallow-water origin is sufficiently proved by the presence of the footprints of terrestrial animals, accompanied in some cases by well-defined "ripple-marks." Along with these are occasionally found ma.s.sive breccias, holding larger or smaller blocks derived from the older formations; and these have been supposed to represent an old "boulder-clay," and thus to indicate the prevalence of an arctic climate. Beds of this nature must also have been deposited in shallow water. In all regions, however, where the Permian formation is well developed, one of its most characteristic members is a Magnesian limestone, often highly and fantastically concretionary, but containing numerous remains of genuine marine animals, and clearly indicating that it was deposited beneath a moderate depth of salt water.

It is not necessary to consider here whether this formation can be retained as a distinct division of the geological series. The name of _Permian_ was given to it by Sir Roderick Murchison, from the province of Perm in Russia, where rocks of this age are extensively developed. Formerly these rocks were grouped with the succeeding formation of the Trias under the common name of "New Red Sandstone." This name was given them because they contain a good deal of red sandstone, and because they are superior to the Carboniferous rocks, while the Old Red Sandstone is inferior.

Nowadays, however, the term "New Red Sandstone" is rarely employed, unless it be for red sandstones and a.s.sociated rocks, which are seen to overlie the Coal-measures, but which contain no fossils by which their exact age may be made out. Under these circ.u.mstances, it is sometimes convenient to employ the term "New Red Sandstone."

The New Red, however, of the older geologists, is now broken up into the two formations of the Permian and Tria.s.sic rocks--the former being usually considered as the top of the Palaeozoic series, and the latter const.i.tuting the base of the Mesozoic.