Page:Quarterly Journal of the Geological Society of London, vol. 25.djvu/72

2 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 11, In alluding to the highly important researches of that good palaeontologist Schmidt, who has been exploring several parts of Siberia, Count Keyserling states that he is of opinion that the chief masses of the Secondary deposits which have been observed in Northern Siberia are not, as Eichwald supposes, of Cretaceous age, but that on closer examination their fossils will be found to agree with those of Oolitic or Jurassic type, of which an account is given by Keyserling in 'Russia in Europe and the Ural Mountains,' i. e. the remains derived from the Petchora region, which is the next adjacent tract on the west to the Siberian region in question.

This view is maintained by the fact that Lindstrom has described exactly analogous fossils from Spitzbergen, from rocks which overlie Triassic deposits. At the same time it is to be noted that these fossils are somewhat peculiar, and should be classed as the Arctic types of the Mesozoic formations of that age.

It has been ascertained by M. Schmidt that the banks of the Jenissei, as well as those of some of its affluents, are occupied by Postpliocene accumulations, similar to those which my associates and self found lying on Palaeozoic limestones at Ust Vaga and other places on the borders of the great river Dwina, at Archangel.

I have called attention to these recent observations, because from them we learn that the classification which my friends and self applied to Russia in Europe has a still wider application, extending far to the Asiatic side of the Ural Mountains. That zone of eruptive, disturbed, and metamorphic rocks being passed over, many of the sedimentary formations which occupy wide spaces in Europe, reappear again in their normal European characters, and occupy vast spaces in Siberia.

It is right to add that M. Schmidt (whose health, I regret to hear, suffered much in making these adventurous journeys) has come to the conclusion that Mammoths lived in Northern Siberia; for, judging from the remains of the fossil and semifossil trees of the region, he infers that in the days of those huge elephants the climate of Siberia was somewhat more temperate than at present, and that after the Glacial epoch the cold was for a time mitigated.

These additional data respecting the extension into Siberia of vast and slightly undulating, and to a great extent horizontal and unbroken formations, which each respectively occupy such wide areas, lead to the inquiry what can have been the deep-seated cause which, excepting along the north and south axis of the Ural Mountains, has prevented the extrusion through the crust of the globe of those igneous rocks which have at various periods so highly diversified the outlines of numerous geological formations in many other parts of the globe.

When speculating on the intervening matter which may have checked the issue of such igneous materials over so wide an area, the late Leopold von Buch once suggested to me, in conversation, that possibly at some very remote period a vast sheet of hypersthene or other submarine volcanic matter may have so spread over the surface of the lower or more central regions of the Palaeozoic deposits as, on