134 Mr. Murchison on the Ural Mountains. 



refer any portion of certain red strata which partly overlie the Per- 

 mian rocks to the " hunter sandstein,'' or new red sandstone of 

 geologists. 



True lias has not yet been seen, but the Jurassic system is clearly 

 divisible into upper and lower formations, and is followed by the 

 cretaceous and tertiary systems, the latter including eocene, mio- 

 cene and pliocene shells, and all these groups are copiously developed 

 and clearly recognisable by their respective mollusca. 



The geological survey of the flat regions of Russia, add the 

 authors, in affording the best proof which has yet been obtained in 

 any part of the world of the same extent, that distinct forms of animal 

 life were successively created and entombed in each succeeding de- 

 posit, has also demonstrated that the successive obliteration of these 

 classes was not caused by the outburst of contiguous plutonic rocks 

 or great physical disturbances of the strata ; for in this region, as 

 large as the whole of those districts of the continent of Europe where 

 geology has been most studied, no intrusive rocks are visible, and 

 the wide-spread formations from the Silurian to the youngest ter- 

 tiary, which must have occupied so vast a lapse of time in their ac- 

 cumulation, as well as the beds of retired modern seas, all repose 

 conformably upon each other. And yet with this regular sequence 

 throughout so vast a series and the absence of any great ruptures, 

 the contents of each succeeding system of older strata are as clearly 

 separable from each other as in those parts of the world where 

 younger rocks are incumbent on the uplifted edges of those which 

 had been previously dislocated. 



But whilst they offer no traces of great and violent upheavals, 

 the horizontal rocks of Russia bespeak most clearly that their sur- 

 face has been so far acted upon by elevatory or subsiding movements, 

 that in some tracts great thicknesses of strata are omitted. Bounded 

 as this large geographical basin has been in remote epochs by the plu- 

 tonic eruptions of Lapland and Sweden on the north, of the Ural on 

 the east, of the granitic steppe on the south, and of the trappean 

 rocks of Poland and Silesia on the west, it is possible, however, 

 that the changes which were evolved in these regions may have 

 affected and influenced the distribution of animal life in the great 

 Muscovite depression which they surrounded. As every geological 

 phenomenon in the strata of the plains of Russia indicates a sub- 

 marine succession, so does the surface announce the same conditions. 

 In the far northern districts the bottom of the Arctic Sea has been 

 shown, by the presence of many existing species of shells, to have 

 once extended over a wide tract of land, now 150 or 200 feet above 

 the sea-level ; and in the south-west it is known by like proofs that 

 the Caspian once covered still wider districts of the steppes. Again, 

 the authors have endeavoured to show that the mammoth alluvia, 

 the boulders of the North and the black earth of Central and South- 

 ern Russia, have all been accumulated under water. 



In reference to the question of the transport of the northern 

 blocks, the authors conceive that their last survey has tended very 

 materially to strengthen the opinions which they previously ex- 

 pressed, that such material* were carried to their present position* 



