Изображения страниц
PDF
EPUB

from the fish proper to these labyrinthodont reptiles that come boldly into force in the Permian and triassic eras.

[merged small][merged small][merged small][graphic]

Fin Spines: 1, Pleuracanthus; 2, Gyracanthus; 3, Ctenacanthus.

Palatal Teeth:

4, Ctenoptychius; 5, Psammodus; 6, Poecilodus. 7, Jaw of Rhizodus,
showing Reptilian Teeth.

The course of vitality is thus for ever onward and upward -onward in the introduction of forms having more varied geographical adaptations, and upward in the manifestation of higher physiological and functional performance.

Such is the panorama of carboniferous life-an unparalleled exuberance of endogenous flora; a wonderful profusion of estuarine and marine life in all its aspects: but as yet few insects, none of the higher reptiles, no birds, no mammals! And yet, looking at mere external conditions, it is

difficult to conceive how, in some of their specific forms, they should not be there. There was abundant food for insects-why not insectivorous reptiles and mammals to prey upon them? Besides insects, there were also fruits and seeds-why not birds to feed upon them; and why not the larger herbivorous reptiles and quadrupeds to browse upon the excess of vegetation that then clothed so large a portion of the earth's surface? True, such plants as equisetums, club-mosses, ferns, and coniferous trees, are, from the peculiar principles they contain, the least fitted for the sustenance of known animals; but then there were the succulent shoots and roots of palms, of calamites, poacites, and other leafy herbage—the fruits of palms and other allied trees, and these we know are the favourite food of many mammals at the present day. Nay more; as we know that certain savage tribes exist on palm fruits, or farinaceous roots, and on the fish of the ocean, we might carry this sort of reasoning still further, and ask whether the human race, in some of its lowlier phases, might not also have been participators in the life of the carboniferous era? To questions such as these the paleontologist has no other answer to offer than that he has hitherto failed to detect the remains of birds and mammals; that as the food to be consumed and the consumer are generally concomitants, so he more than expects the discovery of higher life during the coal-period; but that this higher life, though discovered to-morrow, would necessarily take its stand lower in the scale of organisation than the reptiles, and birds, and mammals which are found in the immediately succeeding formations of the new red sandstone and oolite. If there is one truth that geology has established more clearly than another, it is that of the progressive evolution of life on this globe; not progress from imperfection to perfection, for all are alike fitted to the end for which they were created, but progress from

simpler to more specialised forms. All the discoveries that have been made, and are daily making, never controvert in the least this great order of life; nor do the ablest geologists, though anticipating many new forms, ever expect to find it otherwise with creation than onward and still upward. In this respect the coal-formation takes its place orderly and in perfect harmony with what is known of other formations:—more prolific and more specialised in its forms than the old red sandstone beneath, and less so than the new red and other secondary strata that follow.

Looking, in the mean time, at the whole aspects of the carboniferous period, we are reminded (as we have elsewhere* indicated) of geographical conditions never before nor since exhibited on our globe. The frequent alterna

tions of strata, and the great extent of our coal-fields, indicate the existence of vast estuaries and inland seas— -of gigantic rivers and periodical inundations; the numerous coal-seams and bituminous shales clearly bespeak conditions of soil, moisture, and warmth favourable to an exuberant vegetation, and point partly to vegetable drift, and partly to submerged forests, to peat-swamps and jungle-growth; the mountain limestone, with its marine remains, reminds us of low islands fringed with encrinite-banks and coralreefs, and lagoons thronged with shell-fish and fishes; the existence of reptiles and insects tells us of air, and sunlight, and river-banks; the vast geographical extent of the system bears evidence of an equable and continuous climate over a large portion of the earth's surface; while the interstratified trap-tuffs, the basaltic outbursts, and the numerous faults and fissures, testify to a period of intense igneous activity within the same areas, to repeated upheavals of sea-bottom and submergences of dry land. All this is so clearly indicated to the investigator of the carboniferous system, that

* Advanced Text-Book of Geology.

he feels as convinced of their occurrence as if he had stood on the river-bank of the period, and seen the muddy current roll down its burden of vegetable drift; threaded the channels of the estuary, gloomy with the gigantic growth of swamp and jungle; or sailed over the shallow waters of its archipelago, studded with reef-fringed volcanic islands, and dipped his oar into the forests of encrinites that waved below.

The Permian period, to which we now turn, presents itself more in the light of a new rock-formation than a distinct life-period. Many of its forms are identical with those of the coal period, and we may, without doing great violence to fact, regard it as the continuation and close of the carboniferous era-specialised by local disturbances in the areas of deposit, and the consequent dying out of many genera and species. Perhaps the most remarkable feature is the rapid disappearance of the coal flora, and its restriction to a few higher forms of tree-ferns and coniferous trees, as if the low swampy jungle had been upheaved into higher and drier lands unfavourable to the growth of

2

1

1, Palæoniscus Frieslebeni 2, Platysomus striatus

sigillaria, calamites, equisetums, and lepidodendra. The gigantic sauroid fishes have also disappeared with the

estuaries in which they held supreme sway, though less localised forms, as paleoniscus and platysomus, still occur in abundance; reptiles of larger growth and curious configuration (labyrinthodon) come into view; reptilian and bird-like footsteps (ichnites) can also be traced on the sandstones; and if American geologists be not mistaken, manımalian life in its lowly marsupial form (dromatherium) now comes for the first time on the stage of being. On the whole, however,

Jaw of Dromatherium silvestre, from the Red Sandstones
of North Carolina (Emmons).

there seems a paucity of life during the Permian period, when compared with that which preceded it; and this we may, in the mean time, ascribe partly to geographical changes in the distribution of sea and land, partly to the altered composition of the sea-water in certain areas where we have now magnesian limestones and red ferruginous sandstones, and partly to that change of climate which is indicated by the symptoms of glacial action in the formation of its conglomerates and bouldery breccias.*

* Professor Ramsay, who was the first to advocate, in a decided manner, the glacial origin of these breccias, founds his belief on the following evidences:-1. The great size of many of the fragments-the largest observed weighing (by a rough estimate) from a half to three-quarters of a ton. 2. Their forms. Rounded pebbles are exceedingly rare. They are angular or sub-angular, and have those flattened sides so peculiarly characteristic of many glacier-fragments in existing moraines, and also of many of the stones of the pleistocene drifts, and the moraine matter of the Welsh, Highland, Irish, and Vosges glaciers. 3. Many of them are highly polished, and others are grooved and finely striated, like the stones of existing Alpine glaciers, and like those of the ancient

« ПредыдущаяПродолжить »