صور الصفحة
PDF
النشر الإلكتروني

into Syria, Egypt and Africa, and communicated with the Atlantic by a strait, where now is the valley of the Garonne and the basin of Bordeaux. The Black Sea was connected to a long gulf up the vale of the Danube. Land stood up in this large tract of ocean only in small islands or much ramified masses, where now appear the mountains in the centre of France, in Germany, on the borders of Bohemia and Moravia, in the Hartz, and Carpathians. The British Isles formed almost a complete western boundary, while small points and narrow ridges of land marked the rising Alps and Apennines, and the mountains of Dalmatia and Croatia.

In a far earlier period, after the deposition of the Carboniferous Strata, many of the great features of the British Isles and Scandinavia had been firmly fixed by the axes of elevation which range northeastward from Ireland, through Scotland to the Norwegian Alps, and eastward along the south of Ireland and the south of England, through Belgium, and across the Valley of the Rhine; this last tract was afterwards sunk again and partly covered up by secondary and tertiary deposits, but the former was never again wholly submerged.

But in the still earlier Cambro-Silurian period, the broad ocean flowed over nearly every part of the area now occupied by land in the whole of the northern

zones, most probably here and there diversified by primitive islands, whose situation, however, and constitution are merely conjectural, till we arrive at the series of Wenlock rocks in the Malvern hills. Here is proof of land situated where now is the ridge of the Worcester Beacon; land from which fell, into the sea of that period, rocky fragments precisely the same in nature as the variable Syenites of that ridge; fell into tranquil and slightly agitated water of small depth, and were there cemented together with Corals, Crinoids, Shells and Trilobites, a venerable and interesting mark of the ancient limit of the old and populous sea, against the old perhaps uninhabited land. Accustomed, in this way, to regard the northern seas of our time as the shrunk and ramified remainders of wider tracts of ocean, and the lands as amplified by comparatively modern desiccation round primitive peaks and ridges, we naturally turn to consider whether the forms of life in the sea manifest any special affinity to the fossils of the neighbouring tracts from which it has withdrawn ; and in what degree the plants and animals which now cover the land are related to those which occupied smaller spaces in the same regions.

Taking for a favourable illustration the Germanic Ocean, and comparing its Mollusca with those of the adjoining Pleiocene Crag, on the eastern coast of

England, Deshayes found about 40 per cent. of the Crag shells identical with living species, and of these nearly all occur in the neighbouring ocean'. In like manner, the Tertiary fossils of the sub-Apennine region of Italy are successfully compared with those of the modern epoch, yielding, according to Deshayes, 41.8 per cent. of living species, a large proportion of them from the neighbouring seas2. By observations of this kind, the Tertiary Series is linked in easy harmony with the actual period; but if we make the same kind of comparison of the Tertiary with preceding Mollusca, but little of direct affinity can be traced; and the same remark applies to the common bound

1 See Lyell's Principles of Geology; Wood, in Pal. Soc. Memoirs.

From the copious fauna which now tenants the Mediterranean waters, a series of changes may be traced, through older sea-beds of the same area, far back into bygone ages. Nowhere do we find better illustration than here of the nature of the changes which a fauna may undergo in time: the evidence is consecutive. It is possible, however, that the Mediterranean series, recent and fossil, may be imperfect, and that the earliest periods of our European marine fauna are not represented there. A comparison of the contents of the older Italian deposits, and their equivalents containing the remains of the existing Atlantic species of Testacea, with those of the Faluns of Bordeaux and Touraine, suggests the probability that in these last we have an earlier stage still in the history of our fauna, referable to the time when the Mediterranean depression had not yet been opened to the Atlantic waters.'-Forbes and Godwin-Austen, Nat. Hist. of European Seas, 1859.

ary of the Mesozoic and Palæozoic Deposits, not many closely related forms passing the limits in either case. The present age is in fact a part of the great Cenozoic period.

The attention of Linnæus was drawn to the other question regarding the succession of forms on the land, and in the Amonitates Academica, which contain some essays from his own hand, and many contributed by his pupils, we find an interesting discourse on the subject of the extension of life from the centres of mountainous districts'. It is easy to find examples of parallel forms of Mammalia now living, with some of the Tertiary quadrupeds once denizens of the same regions, or regions formerly connected by land; the affinities thus traced being feebler in proportion to the antiquity of the earlier forms. Thus, in England the Beaver is extinct, but yet lives in Germany; our Red Deer is apparently the same as some Pleistocene fossils, and very similar to others of earlier date; and our European Wolf is found in the ossiferous caverns of England, Germany and France. Sometimes, without this close affinity, a considerable resemblance is found between special tribes now living and others fossil in the same region. In a part of the Continent of America this is remarkable, among the Edentata, which though

1 De telluris orbis incremento.

not quite confined to that region, are more plentiful there than elsewhere, and are successors of fossil races also found almost exclusively in that country. Thus the fossil Megatherium has been compared with the Sloth, the Glyptodon with the Armadillo; nor does the enormous bulk of the fossils hinder the reception of them into the same natural families. The same lands then have been in successive periods peopled by analogous races, and thus we have manifested 'a wonderful relationship on the same continent between the dead and the living. Still this succession of similar forms is limited to Cenozoic ages.

One other example must suffice. The marsupial peculiarity of Australian Mammalia is not of modern date; the Australian caves contain evidence of the same character in the races whose remains are there preserved. The peculiarity indeed is of far earlier origin, for it occurs in the Eocene deposits of the basin of Paris, in the Lacustrine deposits over the upper Oolite in Purbeck, in the lagoon of the great Oolite at Stonesfield, and probably in the Trias of

1 Darwin. This author does not suppose the living Edentata of the same region to be the dwarfed descendants of these monstrous beasts, but speaks of some others, their contemporaries in time and companions in the same caverns, which may be regarded as the progenitors of the living species.

« السابقةمتابعة »