THE PERMIAN PERIOD.
The Permian formation closes the long series of the Palæozoic
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 destitute 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 massive
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 associated 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 circumstances,
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 Triassic rocks--the
former being usually considered as the top of the Palæozoic series,
and the latter constituting the base of the Mesozoic.
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 pass upwards conformably
into the Trias. The division, therefore, between the Permian
and Triassic rocks, and consequently between the Palæozoic 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 accumulated 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, constituting 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 constituted by massive 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):--
[Illustration: 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 Palæozoic
and Mesozoic epochs.
[Illustration: 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
Palæozoic 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, Equisetites, 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 Palæozoic
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 Palæozoic
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.
[Illustration: 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 principal 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 principal 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.
[Illustration: Fig. 136.--_Arca antiqua_. Permian.]
The _Univalves_ (_Gasteropoda_) are rare, and do not demand special
notice. It may be observed, however, that the Palæozoic 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 Palæozoic
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_.
[Illustration: 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 Palæozoic 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 principal
genera of the Ganoids are _Paloeoniscus_ and _Platysomus_ (fig.
137).
The _Amphibians_ of the Permian period belong principally 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_).
[Illustration: 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 class,
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 horny 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 Triassic 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 palæontological 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 Triassic 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 _Palæosaurus_ discovered in the dolomitic
conglomerates near Bristol will be considered as Triassic, thus
leaving _Protorosaurus_[20] as the principal 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 vertebræ 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 Triassic 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' (Palæontographical
Society). King.
(8) 'Monograph of the Permian Brachiopoda of Britain'
(Palæontographical 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 Germaniæ.' Goldfuss.
(12) 'Beiträge zur Petrefaktenkunde.' Munster.
(13) 'Ein Beitrag zur Palæontologie des Deutschen Zechsteingebirges.'
Von Schauroth.
(14) 'Saurier aus dem Kupfer-schiefer der Zechstein-formation.' Von
Meyer.
(15) 'Manual of Palæontology.' Owen.
(16) 'Recherches sur les Poissons Fossiles.' Agassiz.
(17) 'Ichnology of Annandale.' Sir William Jardine.
(18) 'Die Fossile Flora der Permischen Formation.' Goeppert.
(19) 'Genera et Species Plantarum Fossilium.' Unger.
(20) "On the Red Rocks of England of older Date than the Trias"
--'Quart. Journ. Geol. Soc.,' vol. xxvii. Ramsay.