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nimal organic remains yet detected in it was a single cale of the Holoptychius found by Mr Murchison; nd though it contains vegetable organisms in more bundance, so imperfectly are they preserved, that little lse can be ascertained regarding them than that they vere land plants, but not identical with the plants of he Coal Measures. In Scotland the formation is ichly fossiliferous, and the remains belong chiefly to he animal kingdom. It is richly fossiliferous, too, in Russia, where it was discovered by Mr Murchison, luring the summer of last year, spread over areas nany thousand square miles in extent. And there, as n Scotland, the Holoptychius is its characteristic fossil. The fact seems especially worthy of remark. The organisms of some of the newer formations differ entirely, in widely-separated localities, from their cotemporary organisms, just as in the existing state of things the plants and animals of Great Britain differ from the plants and animals of Lapland or Sierra Leone. A geologist who has acquainted himself with the belemnites, baculites, turrilites, and sea-urchins of the Cretaceous group in England and the north of France, would discover that he had got into an entirely new field among the hippurites, sphærulites, and nummulites of the same formations, in Greece, Italy, and Spain; nor, in passing to the tertiary deposits, would he find less striking dissimilarities between the gigantic mail-clad megatherium and huge mastodon of the Ohio and the La Plate, and the monsters, their cotemporaries, the hairy mammoth of Siberia, and the hippopotamus and rhinoceros of England and the Continent. In the more ancient

geological periods, ere the seasons began, the case is essentially different; the cotemporary formations, when widely separated, are often very unlike in mineralogical character, but in their fossil contents they are almost always identical. In these earlier ages, the atmospheric temperature seems to have depended more on the internal heat of the earth, only partially cooled down from its original state, than on the earth's configuration or the influence of the sun. Hence a widelyspread equality of climate,-a green-house equalization of heat, if I may so speak; and hence, too, it would seem, a widely-spread Fauna and Flora. The greenhouses of Scotland and Sweden produce the same plants with the green-houses of Spain and Italy; and when the world was one vast green-house, heated from below, the same families of plants, and the same tribes of animals, seem to have ranged over spaces immensely more extended than those geographical circles in which, in the present time, the same plants are found indigenous, and the same animals native. The fossil remains of the true Coal Measures are the same to the westward of the Alleghany Mountains as in New Holland, India, Southern Africa, the neighbourhood of Newcastle, and the vicinity of Edinburgh. And I entertain little doubt that, on a similar principle, the still more ancient organisms of the Old Red Sandstone will be found to bear the same character all over the world.

CHAPTER IX.

Fossils of the Upper Old Red Sandstone much more imperfectly preserved than those of the Lower.-The Causes obvious.-Difference between the two Groupes, which first strikes the Observer, a Difference in Size.-The Holoptychius a characteristic Ichthyolite of the Formation.-Description of its huge Scales.-Of its Occipital Bones, Fins, Teeth, and general Appearance.-Cotemporaries of the Holoptychius.— Sponge-like Bodies.-Plates resembling those of the Sturgeon.-Teeth of various Forms, but all evidently the Teeth of Fishes.-Limestone Band and its probable Origin.-Fossils of the Yellow Sandstone.-The Pterichthys of Dura Den.— Member of a Family peculiarly characteristic of the System. No intervening Formation between the Old Red Sandstone and the Coal Measures.—The Holoptychius cotemporary for a time with the Megalichthys.-The Columns of Tubal Cain.

THE different degrees of entireness in which the ggeologist finds his organic remains, depend much less on their age than on the nature of the rock in which they occur; and as the arenaceous matrices of the Upper and Middle Old Red Sandstones have been less favourable to the preservation of their peculiar fossils than the calcareous and aluminous matrices of the Lower, we frequently find the older organisms of the system fresh and unbroken, and the more modern existing as mere fragments. A fish thrown into

a heap of salt would be found entire after the lapse of many years; a fish thrown into a heap of sand would disappear in a mass of putrefaction in a few weeks; and only the less destructible parts, such as the teeth, the harder bones, and perhaps a few of the scales, would survive. Now, limestone, if I may so speak, is the preserving salt of the geological world; and the conservative qualities of the shales and stratified clays of the Lower Old Red Sandstone are not much inferior to those of lime itself; while, in the Upper Old Red, we have merely beds of consolidated sand, and these, in most instances, rendered less conservative of organic remains than even the common sand of our shores, by a mixture of the red oxide of iron. The older fossils, therefore, like the mummies of Egypt, can be described well nigh as minutely as the existences of the present creation; the newer, like the comparatively modern remains of our churchyards, exist, except in a few rare cases, as mere fragments, and demand powers such as those of a Cuvier or an Agassiz to restore them to their original combinations.

But cases, though few and rare, do occur in which, through some favourable accident connected with the death or sepulture of some individual existence of the period, its remains have been preserved almost entire ; and one such specimen serves to throw light on whole heaps of the broken remains of its cotemporaries. The single elephant, preserved in an iceberg beside the Arctic Ocean, illustrated the peculiarities of the numerous extinct family to which it belonged, and whose bones and huge tusks whiten the wastes of Siberia. The human body found in an Irish bog, with

he ancient sandals of the country still attached to its eet by thongs, and clothed in a garment of coarse air, gave evidence that bore generally on the degree of civilization attained by the inhabitants of an entire listrict in a remote age. In all such instances the character and appearance of the individual bear on hose of the tribe. In attempting to describe the organisms of the Lower Old Red Sandstone, where the fossils lie as thickly in some localities as herrings on Our coasts in the fishing season, I felt as if I had whole tribes before me. In describing the fossils of the Upper Old Red Sandstone I shall have to draw mostly from single specimens.

equally sound so far as it

But the evidence may be goes.

The difference between the superior and inferior groupes of the system which first strikes an observer, is a difference in the size of the fossils of which these groupes are composed. The characteristic organisms of the Upper Old Red Sandstone are of much greater bulk than those of the Lower, which seem to have been characterized by a mediocrity of size throughout the entire extent of the formation. The largest ichthyolites of the group do not seem to have much exceeded two feet or two feet and a half in length; its smaller average from an inch to three inches. A jaw, in the possession of Dr Traill,—that of an Orkney species of Holoptychius, and by much the largest in his collection, does not exceed in bulk the jaw of a full-grown coal-fish or cod; his largest Coccosteus must have been a considerably smaller fish than an ordinary-sized turbot; the largest ichthyolite found by the writer was a Diplopterus, of, however, smaller

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