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Romance of Modern Geology

<h2 class="nobreak" id="CHAPTER_XIX">CHAPTER XIX</h2> <h3>THE AGE OF REPTILES</h3></div> We have already said that in the many hundreds of thousands of years which went by during Carboniferous times the sea sometimes advanced and sometimes receded, and nothing shows this better than the great thickness of the deposits in which the coal lies in seams. In America, as in Europe, Asia, Africa, Australia, and New Zealand, South and Central America, the Carboniferous system is found. In Arkansas, in North America, the coal measures attain the remarkable thickness of 18,000 feet; in the Wasatch Mountains the Carboniferous strata have been estimated to be 13,000 feet thick, and in silver-bearing Nevada 10,000 feet. The formations of the Western European coal measures, like those of Eastern North America, consist principally of shales and clays, with smaller amounts of sandstone and limestone. They attain great thickness, and, including 5500 feet of the Millstone Grit, are 13,500 feet thick in Lancashire and several thousand feet thick in many parts of Great Britain and Ireland. The extraordinary thicknesses show that near our islands must have been a very extensive and lofty area of land. In Germany the same strata, thickly seamed with coal, -227- are 10,000 feet thick. There must also have been considerable volcanic or earthquake action as we know, because in Germany, near the Hartz Mountains and elsewhere, there are many igneous rocks thrust into the strata, and also because in Belgium and in France the coal strata are very much twisted and contorted. The same or similar beds are found in Siberia, in Japan, and in China, where the coal beds are said to be thicker than anywhere else in the world. The Carboniferous system is also found in Africa, in the north, south-east, and south of the continent; and in Australia and New Zealand Carboniferous strata to the thickness of 10,000 feet are indicated. At the close of this period the changes ever taking place transformed the conditions of life in a way the reverse of that which we have hitherto been examining. So far each age has shown an increase of life on the age preceding it. But when the great outburst of carboniferous activity began to wane it was followed by a lessening of the wave of life. As we said in the last chapter, there lie on the top of the coal-bearing strata beds to which the older geologists gave the name of New Red Sandstone. But in 1841 the New Red Sandstone was divided into two distinct geological formations. To the lower and older part Murchison gave in 1841 the name of Permian (from Perm or Permia, an ancient kingdom in Russia, where red sandy rocks of this age form nearly all the surface), but in Germany it is more frequently called the Dyas (from Lat. duo, two), because in that country it is composed of two well-marked -228- divisions—red sandstones below and magnesian limestones above. Thus there are two types of this Permian formation: the Permian type proper—a mixed series of red sandstones, marls, shales, and limestones, with some thin beds of coal, as found in Russia; and the Dyassic type, as seen in Germany. We do not know what brought about the change: though we do know that during it there was great volcanic activity over Europe and that the waning forests of vegetation and the steaming swamps gave place to desert plains. Vegetation sank lower and lower. The forests disappeared or dwelt only in clusters. The soft sappy trees gave place to hardy pines which clung to the plains and the mountains, and other sterner types began to appear, allied to the spruces, yews, and ginkgo. The ginkgo tree is one of the oldest of the tree type which now has a living representative. Any reader interested enough in the matter to walk along Royal Hospital Road, Chelsea, will find a ginkgo tree just outside the Old Physic Garden; and of course a good many other examples are preserved in botanic gardens. The cycads, offshoots of the ferns, through the strange group of trees known as the cycado-filices, spread through the woods. The trilobites, to turn to animal life, all but disappeared, though one elegant example remained; the corals were changing; and the lamp-shells were dropping out. There were a few new species of fishes, but none of any great strength or capacity, and all preserving still the tail which is part of the backbone. There was an all-round impoverishment of life—so great, indeed, that the -229- early geologists used to believe that a complete destruction of all life followed this, the closing stage of the Palæozoic era, and that a re-creation followed. They would have been confirmed in this belief had they but known that intense cold and glaciation were setting in where the tropics were situated and that the dryness of vast deserts was sweeping away life elsewhere. But we now know that life was not entirely lost; that many species survived, and that others, altering to suit altering conditions, became stronger in the process. Nevertheless, life was greatly impoverished. A census made a few years ago gave the known animal species of the Carboniferous period as 10,000, while those of the Permian period were only 300, or three per cent. Possibly the percentage was larger than that, but still it was small. But if the Permian was poor in life it was very interesting. The amphibians had been growing in strength during the later stages of the Carboniferous age, and may possibly have been more numerous then than at any other time, for the vast swamps were very favourable for them. They diminished in the Permian, though the Permian amphibians showed some advances, and began to assume a likeness to reptiles. Perhaps the reptiles may have first appeared in the Carboniferous, but they declared themselves in the Permian age. Two great branches of reptiles seem already to have defined themselves; perhaps they had never formed a common group as reptiles, but had separated while still amphibians. The one bore resemblance to, and were perhaps the forerunners of, the great hosts of lizards, crocodiles, dinosaurs, -230- ichthyosaurs, and flying saurians, which are the most pronounced of the reptiles, and of which we shall have a great deal to say presently. The other group were perhaps the ancestors of the turtles and plesiosaurs which appeared later, and possibly led the way to the mammals. This rapid and diverse spreading out of the reptiles in a period when life as a whole was at a low ebb is not a little remarkable. These creatures seem to show the arrival of a more pronounced form of air-breathing animal; and that may have been the consequence of the presence of more oxygen in the earth's atmosphere. Of the Permian amphibians, one of the most interesting was like the Sphenodon, which still creeps about the northern islands of New Zealand. The most striking of the reptiles was the Naosaurus, a beast-like creature with a high back of spines webbed together like a solid porcupine. It was from three to ten feet in length. All these changes were brought about by the general withdrawal of the sea, both in the North American continent and in Europe. In both continents there are beds which accumulated fresh water; in both beds which were laid down in salt lakes or inland seas; and in both beds which were laid down on the floor of seas washing the continents. Great areas seem to have been sometimes dry and sometimes submerged; other and greater areas, bordered by ice and sometimes swept by icy blasts, or subject to burning sun in summer, were deserts such as we are aware of now in Asia or North Africa or mid-Australia, but much larger in extent than any of these. It was in conditions such as these that the ancient -231- or Palæozoic rocks came to an end and the Mesozoic or Middle Period began. The Middle period of strata and of the life which those strata have preserved has usually been separated from the older rocks because, owing to the great period of arid desert conditions, the character of life changed a great deal; but fuller knowledge shows that the links were still there, and that ceaseless adaptation of animals to their surroundings was ceaselessly going on. We need not follow closely all the changes and relationships, and only much greater knowledge than geologists yet possess will enable them to trace all the alterations of the land and sea. But we may trace the alterations in the appearance of the continents in broad outline. Nearly the whole extent of the British Isles was now above the sea, and was enjoying a climate perhaps as cold as present-day Iceland. To the south and east of Scotland was a great shallow inland lake, while north of Great Britain a huge plain stretched across Europe. To the south of the lake was a belt of land, and farther south still the sea had invaded Italy and reached to Southern Germany, and in this sea was being laid down the limestone which in later eras was to be elevated into the mountains of the Apennines, the Alps, and the Pyrenees. North Africa was under water, but farther south the uplifted lands were joining hands with India. Sea swept part of Asia, but North America was larger and broader than it is now, her western coast stretching farther out into the ocean. In this period, which is called the Triassic (the name given to it by the German geologist Bronn because of the -232- three distinct beds he found in it, though the middle of these, a shelly limestone, does not exist in Great Britain), there was a wide development of large reptiles and amphibians. We cannot enumerate them all, for not one chapter nor one volume would suffice to deal adequately with the reptiles of the Trias formations and of the Jurassic rocks which followed them, and of the Permian which preceded them. But we may speak of some of them. One of the most striking was the Pareiasaurus, which has been found in the Jurassic sandstones and limestones of South Africa, of Russia, of India and Scotland, and of middle England. The skeleton of the Pareiasaurus looks like that of a gigantic pug dog eight feet long; but it was a comparatively harmless animal, the teeth of which show that it largely fed on vegetable food. In Sir E. Ray Lankester's lectures on "Extinct Animals" he described the finding of a great many of these fossil reptiles by Professor Amalitzky on the banks of the River Dwina, near Archangel. There is a cliff of Permian strata on the banks of the Dwina, and in this cliff there is a peculiar pocket or accumulation of sandy matter with large hard nodules embedded in it. These nodules are removed and broken up for mending the roads. The pocket seems to be in a fissure and of Triassic age, later, that is to say, than the Permian rocks on either side of it. However that may be, the nodules are usually removed for road-mending, and four or five years ago Professor Amalitzky on visiting the spot was astounded and delighted to find that -233- when broken each nodule was seen to contain the skeleton or skull of a great reptile. The Russian geologist determined to make a most thorough investigation of this wonderful deposit, and for years spent several thousand pounds in having the nodules dug out by the peasants after the year's farming work was over, and in removing them to the University of Warsaw, where with the finest instruments and greatest care the nodules are opened, and each bone removed in fragments is put together from its more or less broken parts, and firmly cemented and set up in its natural position as a complete skeleton. These Pareiasaurs reconstructed by Professor Amalitzky were about as big as well-grown cattle, but not so high on the legs. Living at the same time, and its skeleton now found near them, was an enormous and truly terrible flesh-eating animal, with a skull two feet long and enormous tiger-like teeth. This creature was named Inostransevia. No doubt the vegetarian herds of Pareiasaurus, whose small peg-like teeth indicate their harmlessness, were preyed on by the terrible Inostransevia, as were their brethren in South Africa devoured by other carnivorous reptiles of that remote Triassic age. So we see the co-existence of blood-sucker and victim—of the destructive oppressor and the helpless oppressed—forced on our attention in these two localities, Russia and South Africa, in days long before man was. Other land forms were grotesque and curious in shape, the Chelonians for example, big birds and crocodiles rolled into one, and clothed in lizard-like skin—queer pear-shaped brutes with -234- huge hind limbs, short fore limbs, narrow chests, and pigmy skulls. Both branches of the reptilian horde, those representing the saurians and those which were the forerunners of the mammals, sent delegations to the sea before the close of the Triassic period. The Ichthyosaurs represented the more pronounced reptilian line; the Plesiosaurs were the representatives of the coming mammals. It is not difficult to find good reason for this movement to the sea. Besides the inevitable tendency of every masterful race to invade all accessible realms, the renewed extension of the sea that set in during the Triassic period and became pronounced before its close, especially invited this, for the shallow waters creeping out upon the land with their now prolific life set tempting morsels before the voracious reptiles, on the one hand, while on the other, the reduction of the land area and the restriction of their feeding-grounds, intensified by the multiplication of the reptiles themselves, forced a resort to the sea. One of the reptiles of this period, the Lariosaurus, shows by its development how the change affected the reptiles. In the earlier stages of the Trias it resembled a rather swollen alligator with four limbs symmetrically situated and used for crawling. In the later forms of these reptiles the limbs were modified with paddles, and all power to move about on land was lost. <hr class="chap x-ebookmaker-drop" /> -235- <div style="break-after:column;"></div>

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