The Ancient Life History of the Earth Part 14

In many instances, the Permian rocks are seen to repose unconformably upon the underlying Carboniferous, from which they can in addition be readily separated by their lithological characters. In other instances, however, the Coal-measures terminate upwards in red rocks, not distinguishable by their mineral characters from the Permian; and in other cases no physical discordance between the Carboniferous and Permian strata can be detected. As a general rule, also, the Permian rocks appear to pa.s.s upwards conformably into the Trias. The division, therefore, between the Permian and Tria.s.sic rocks, and consequently between the Palaeozoic and Mesozoic series, is not founded upon any conspicuous or universal physical break, but upon the difference in life which is observed in comparing the marine animals of the Carboniferous and Permian with those of the Trias. It is to be observed, however, that this difference can be solely due to the fact that the Magnesian Limestone of the Permian series presents us with only a small, and not a typical, portion of the marine deposits which must have been acc.u.mulated in some area at present unknown to us during the period which elapsed between the formation of the great marine limestones of the Lower Carboniferous and the open-sea and likewise calcareous sediments of the Middle Trias.

The Permian rocks exhibit their most typical features in Russia and Germany, though they are very well developed in parts of Britain, and they occur in North America. When well developed, they exhibit three main divisions: a lower set of sandstones, a middle group, generally calcareous, and an upper series of sandstones, const.i.tuting respectively the Lower, Middle, and Upper Permians.

In Russia, Germany, and Britain, the Permian rocks consist of the following members:--

1. The _Lower Permians_, consisting mainly of a great series of sandstones, of different colours, but usually red. The base of this series is often const.i.tuted by ma.s.sive breccias with included fragments of the older rocks, upon which they may happen to repose; and similar breccias sometimes occur in the upper portion of the series as well. The thickness of this group varies a good deal, but may amount to 3000 or 4000 feet.

2. The _Middle Permians_, consisting, in their typical development, of laminated marls, or "marl-slate," surmounted by beds of magnesian limestone (the "Zechstein" of the German geologists). Sometimes the limestones are degenerate or wholly deficient, and the series may consist of sandy shales and gypsiferous clays. The magnesian limestone, however, of the Middle Permians is, as a rule, so well marked a feature that it was long spoken of as _the_ Magnesian Limestone.

3. The _Upper Permians_, consisting of a series of sandstones and shales, or of red or mottled marls, often gypsiferous, and sometimes including beds of limestone.

In North America, the Permian rocks appear to be confined to the region west of the Mississippi, being especially well developed in Kansas. Their exact limits have not as yet been made out, and their total thickness is not more than a few hundred feet.

They consist of sandstones, conglomerates, limestones, marls, and beds of gypsum.

The following diagrammatic section shows the general sequence of the Permian deposits in the north of England, where the series is extensively developed (fig. 133):--

[Ill.u.s.tration: Fig. 133. GENERALISED SECTION OF THE PERMIAN ROCKS IN THE NORTH OF ENGLAND.]

The record of the _life_ of the Permian period is but a scanty one, owing doubtless to the special peculiarities of such of the deposits of this age with which we are as yet acquainted. Red rocks are, as a general rule, more or less completely unfossiliferous, and sediments of this nature are highly characteristic of the Permian.

Similarly, magnesian limestones are rarely as highly charged with organic remains as is the case with normal calcareous deposits, especially when they have been subjected to concretionary action, as is observable to such a marked extent in the Permian limestones.

Nevertheless, much interest is attached to the organic remains, as marking a kind of transition-period between the Palaeozoic and Mesozoic epochs.

[Ill.u.s.tration: Fig. 134.--_Walchia piniformis_, from the Permian of Saxony, a, Branch; b, Twig, (After Gutbier.)]

The _plants_ of the Permian period, as a whole, have a distinctly Palaeozoic aspect, and are far more nearly allied to those of the Coal-measures than they are to those of the earlier Secondary rocks; though the Permian _species_ are mostly distinct from the Carboniferous, and there are some new genera. Thus, we find species of _Lepidodendron, Calamites, Equiset.i.tes, Asterophyllites, Annularia_, and other highly characteristic Carboniferous genera.

On the other hand, the _Sigillariods_ of the Coal seem to have finally disappeared at the close of the Carboniferous period. Ferns are abundant in the Permian rocks, and belong for the most part to the well-known Carboniferous genera _Alethopteris, Neuropteris, Sphenopteris_, and _Pecopteris_. There are also Tree-ferns referable to the ancient genus _Psaronius_. The _Conifers_ of the Permian period are numerous, and belong in part to Carboniferous genera.

A characteristic genus, however, is _Walchia_ (fig. 134), distinguished by its lax short leaves. This genus, though not exclusively Permian, is mainly so, the best-known species being the _W. Piniformis_. Here, also, we meet with Conifers which produce true cones, and which differ, therefore, in an important degree from the Taxoid Conifers of the Coal-measures. Besides _Walchia_, a characteristic form of these is the _Ullmania selaginoides_, which occurs in the Magnesian Limestone of Durham, the Middle Permian of Westmorland, and the "Kupfer-schiefer" of Germany. The group of the _Cycads_, which we shall subsequently find to be so characteristic of the vegetation of the Secondary period, is, on the other hand, only doubtfully represented in the Permian deposits by the singular genus _Noeggerathia_.

The _Protozoans_ of the Permian rocks are few in number, and for the most part imperfectly known. A few _Foraminifera_ have been obtained from the Magnesian Limestone of England, and the same formation has yielded some ill-understood Sponges. It does not seem, however, altogether impossible that some of the singular "concretions" of this formation may ultimately prove to have an organic structure, though others would appear to be clearly of purely inorganic origin. From the Permian of Saxony, Professor Geinitz has described two species of _Spongillopsis_, which he believes to be most nearly allied to the existing fresh-water Sponges (_Spongilla_). This observation has an interest as bearing upon the mode of deposition and origin of the Permian sediments.

The _Coelenterates_ are represented in the Permian by but a few Corals. These belong partly to the _Tabulate_ and partly to the _Rugose_ division; but the latter great group, so abundantly represented in Silurian, Devonian, and Carboniferous seas, is now extraordinarily reduced in numbers, the British strata of this age yielding only species of the single genus _Polycoelia_.

So far, therefore, as at present known, all the characteristic genera of the Rugose Corals of the Carboniferous had become extinct before the deposition of the limestones of the Middle Permian.

The _Echinoderms_ are represented by a few _Crinoids_, and by a Sea-urchin belonging to the genus _Eocidaris_. The latter genus is nearly allied to the _Archoeocidaris_ of the Carboniferous, so that this Permian form belongs to a characteristically Palaeozoic type.

A few _Annelides_ (_Spirorbis, Vermilia_, &c.) have been described, but are of no special importance. Amongst the _Crustaceans_, however, we have to note the total absence of the great Palaeozoic group of the _Trilobites_; whilst the little _Ostracoda_ and _Phyllopods_ still continue to be represented. We have also to note the first appearance here of the "Short-tailed" Decapods or Crabs (_Brachyura_), the highest of all the groups of _Crustacea_, in the person of _Hemitrochiscus paradoxus_, an extremely minute Crab from the Permian of Germany.

[Ill.u.s.tration: Fig. 135.--Brachiopods of the Permian formation.

a, _Producta horrida_; b, _Lingula Credneri_; c, _Terebratula elongata_; d and e, _Camarophoria globulina_. (After King.)]

Amongst the _Mollusca_, the remains of _Polyzoa_ may fairly be said to be amongst the most abundant of all the fossils of the Permian formation, The princ.i.p.al forms of these are the fronds of the Lace-corals (_Fenestella, Retepora_, and _Synocladia_), which are very abundant in the Magnesian Limestone of the north of England, and belong to various highly characteristic species (such as _Fenestella retiformis, Retepora Ehrenbergi_, and _Synocladia virgulacea_). The _Brachiopoda_ are also represented in moderate numbers in the Permian. Along with species of the persistent genera _Discina, Crania_, and _Lingula_, we still meet with representatives of the old groups _Spirifera, Athyris_, and _Streptorhynchus_; and the Carboniferous _Productoe_ yet survive under well-marked and characteristic types, though in much-diminished numbers. The species of Brachiopods here figured (fig. 135) are characteristic of the Magnesian Limestone in Britain and of the corresponding strata on the Continent. Upon the whole, the most characteristic Permian _Brachiopods_ belong to the genera _Producta, Strophalosia_, and _Camarophoria_.

The _Bivalves_ (_Lamellibranchiata_) have a tolerably varied development in the Permian rocks; but nearly all the old types, except some of those which occur in the Carboniferous, have now disappeared. The princ.i.p.al Permian Bivalves belong to the groups of the Pearl Oysters (_Aviculidoe_) and the _Trigoniadoe_, represented by genera such as _Bakewellia_ and _Schizodus_; the true Mussels (_Mytilidoe_), represented by species which have been referred to _Mytilus_ itself; and the Arks (_Arcadoe_), represented by species of the genera _Arca_ (fig. 136) and _Byssoarca_. The first and last of these three families have a very ancient origin; but the family of the _Trigoniadoe_, though feebly represented at the present day, is one which attained its maximum development in the Mesozoic period.

[Ill.u.s.tration: Fig. 136.--_Arca antiqua_. Permian.]

The _Univalves_ (_Gasteropoda_) are rare, and do not demand special notice. It may be observed, however, that the Palaeozoic genera _Euomphalus, Murchisonia, Loxonema_, and _Macrocheilus_ are still in existence, together with the persistent genus _Pleurotomaria_.

_Pteropods_ of the old genera _Theca_ and _Conularia_ have been discovered; but the first of these characteristically Palaeozoic types finally dies out here, and the second only survives but a short time longer. Lastly, a few _Cephalopods_ have been found, still wholly referable to the Tetrabranchiate group, and belonging to the old genera _Orthoceras_ and _Cyrtoceras_ and the long-lived _Nautilus_.

[Ill.u.s.tration: Fig. 137.--_Platysomus gibbosus_, a "heterocercal"

Ganoid, from the Middle Permian of Russia.]

Amongst _Vertebrates_, we meet in the Permian period not only with the remains of Fishes and Amphibians, but also, for the first time, with true Reptiles. The _Fishes_ are mainly _Ganoids_, though there are also remains of a few Cestraciont Sharks. Not only are the _Ganoids_ still the predominant group of Fishes, but all the known forms possess the unsymmetrical ("heterocercal") tail which is so characteristic of the Palaeozoic Ganoids. Most of the remains of the Permian Fishes have been obtained from the "Marl-slate" of Durham and the corresponding "Kupfer-schiefer" of Germany, on the horizon of the Middle Permian; and the princ.i.p.al genera of the Ganoids are _Paloeoniscus_ and _Platysomus_ (fig.

137).

The _Amphibians_ of the Permian period belong princ.i.p.ally to the order of the _Labyrinthodonts_, which commenced to be represented in the Carboniferous, and has a large development in the Trias.

Under the name, however, of _Paloeosiren Beinerti_, Professor Geinitz has described an Amphibian from the Lower Permian of Germany, which he believes to be most nearly allied to the existing "Mud-eel" (_Siren lacertina_) of North America, and therefore to be related to the Newts and Salamanders (_Urodela_).

[Ill.u.s.tration: Fig. 138.--_Protorosaurus Speneri_, Middle Permian, Thuringia, reduced in size. (After Von Meyer.) [Copied from Dana.]]

Finally, we meet in the Permian deposits with the first undoubted remains of true _Reptiles_. These are distinguished, as a cla.s.s, from the _Amphibians_, by the fact that they are air-breathers throughout the whole of their life, and therefore are at no time provided with gills; whilst they are exempt from that metamorphosis which all the _Amphibia_ undergo in early life, consequent upon their transition from an aquatic to a more or less purely aerial mode of respiration. Their skeleton is well ossified; they usually have h.o.r.n.y or bony plates, singly or in combination, developed in the skin; and their limbs (when present) are never either in the form of _fins_ or _wings_, though sometimes capable of acting in either of these capacities, and liable to great modifications of form and structure. Though there can be no doubt whatever as to the occurrence of genuine Reptiles in deposits of unquestionable Permian age, there is still uncertainty as to the precise number of types which may have existed at this period.

This uncertainty arises partly from the difficulty of deciding in all cases, whether a given bone be truely Labyrinthodont or Reptilian, but more especially from the confusion which exists at present between the Permian and the overlying Tria.s.sic deposits.

Thus there are various deposits in different regions which have yielded the remains of Reptiles, and which cannot in the meanwhile be definitely referred either to the Permian series or to the Trias by clear stratigraphical or palaeontological evidence. All that can be done in such cases is to be guided by the characters of the Reptiles themselves, and to judge by their affinities to remains from known Tria.s.sic or Permian rocks to which of these formations the beds containing them should be referred; but it is obvious that this method of procedure is seriously liable to lead to error. In accordance, however, with this, the only available mode of determination in some cases, the remains of _Thecodontosaurus_ and _Palaeosaurus_ discovered in the dolomitic conglomerates near Bristol will be considered as Tria.s.sic, thus leaving _Protorosaurus_[20] as the princ.i.p.al and most important representative of the Permian Reptiles.[21] The type-species of the genus _Protorusaurus_ is the _P. Speneri_(fig. 138) of the "Kupfer-schiefer" of Thuringia, but other allied species have been detected in the Middle Permian of Germany and the north of England. This Reptile attained a length of from three to four feet; and it has been generally referred to the group of the Lizards (_Lacertilia_), to which it is most nearly allied in its general structure, at the same time that it differs from all existing members of this group in the fact that its numerous conical and pointed teeth were implanted in distinct sockets in the jaws--this being a Crocodilian character. In other respects, however, _Protorosaurus_ approximates closely to the living Monitors (_Varanidoe_); and the fact that the bodies of the vertebrae are slightly cupped or hollowed out at the ends would lead to the belief that the animal was aquatic in its habits. At the same time, the structure of the hind-limbs and their bony supports proves clearly that it must have also possessed the power of progression upon the land. Various other Reptilian bones have been described from the Permian formation, of which some are probably really referable to Labyrinthodonts, whilst others are regarded by Professor Owen as referable to the order of the "Theriodonts," in which the teeth are implanted in sockets, and resemble those of carnivorous quadrupeds in consisting of three groups in each jaw (namely, incisors, canines, and molars). Lastly, in red sandstones of Permian age in Dumfriesshire have been discovered the tracks of what would appear to have been _Chelonians_ (Tortoises and Turtles); but it would not be safe to accept this conclusion as certain upon the evidence of footprints alone. The _Chelichnus Duncani_, however, described by Sir William Jardine in his magnificent work on the 'Ichnology of Annandale,' bears a great resemblance to the track of a Turtle.

[Footnote 20: Though commonly spelt as above, it is probable that the name of this Lizard was really intended to have been _Proterosaurus_--from the Greek _proteros_, first; and _saura_, lizard: and this spelling is followed by many writers.]

[Footnote 21: In an extremely able paper upon the subject (Quart.

Journ. Geol. Soc., vol. xxvi.), Mr Etheridge has shown that there are good physical grounds for regarding the dolomitie conglomerate of Bristol as of Tria.s.sic age, and as probably corresponding in time with the Muschelkalk of the Continent.]

No remains of Birds or Quadrupeds have hitherto been detected in deposits of Permian age.

LITERATURE.

The following works may be consulted by the student with regard to the Permian formation and its fossils:--

(1) "On the Geological Relations and Internal Structure of the Magnesian Limestone and the Lower Portions of the New Red Sandstone Series, &c."--'Trans. Geol. Soc.,' ser. 2, vol. iii.

Sedgwick.

(2) 'The Geology of Russia in Europe.' Murchison, De Verneuil, and Von Keyserling.

(3) 'Siluria,' Murchison.

(4) 'Permische System in Sachsen.' Geinitz and Gutbier.

(5) 'Die Versteinerungen des Deutschen Zechsteingebirges,' Geinitz.

(6) 'Die Animalischen Ueberreste der Dyas.' Geinitz.

(7) 'Monograph of the Permian Fossils of England' (Palaeontographical Society). King.

(8) 'Monograph of the Permian Brachiopoda of Britain'

(Palaeontographical Society). Davidson.

(9) "On the Permian Rocks of the North-West of England and their Extension into Scotland"--'Quart. Journ. Geol. Soc.,' vol. xx.

Murchison and Harkness.

(10) 'Catalogue of the Fossils of the Permian System of the Counties of Northumberland and Durham.' Howse.

(11) 'Petrefacta Germaniae.' Goldfuss.

(12) 'Beitrage zur Petrefaktenkunde.' Munster.

(13) 'Ein Beitrag zur Palaeontologie des Deutschen Zechsteingebirges.'

Von Schauroth.

(14) 'Saurier aus dem Kupfer-schiefer der Zechstein-formation.' Von Meyer.

(15) 'Manual of Palaeontology.' Owen.

(16) 'Recherches sur les Poissons Fossiles.' Aga.s.siz.

(17) 'Ichnology of Annandale.' Sir William Jardine.

(18) 'Die Fossile Flora der Permischen Formation.' Goeppert.