212 
THE GEOLOGIST. 
word Jurassic grate upon the ears of Englishmen, it is impos- 
sible to deny that this geographical term is much more applica- 
ble to the strata in question than our own word ^'^ Oolitic/^ which 
implies a structure scarcely ever seen in beds of this age in 
E/Ussia. Whether examined at Moscow or on the Lower Volga, 
they consist of black shales and ferruginous sands, occasionally 
containing calcareous cement-stones, and thus they present a 
general lithological analogy to the Lias ; a formation, however, 
which is not represented in Russia, for the fossils are all refer- 
able to the groups extending from the Inferior to the Upper 
Oolite, and many of them are identical with British species. 
" I must now pass over the Cretaceous deposits which occupy 
such broad spaces in Southern Russia, the Lower Tertiary beds, 
some of which, on the Volga, might almost be mistaken for those 
of Bognor and the London basin, and also the strata of the 
Miocene age, whish occupy wide tracts in Volhynia and Podolia, 
merely remarking by the way, how the recent discovery in lime- 
stone of an herbivorous Cetacean is a very important adition 
to the fauna of that period. 
Superficial Detritus — Ural Mountains, ^c. — The discovery of 
accumulations, containing recent shells of Arctic species, con- 
siderably to the south of Archangel, was important, as showing 
that the great northern blocks, which overlie them there, were 
brought to their present position during a period which differed 
remarkably from the one preceding it, and also from that which 
has followed it, in the very general prevalence of a colder climate 
over large spaces ; thus enabling us very safely to infer, that the 
great erratics of the North were transported in icebergs, which 
floated in an arctic sea and occasionally grated along its bottom. 
But this operation, gigantic as it was, had its well-defined south- 
ern limits, as is beautifully proved by the general survey of the 
Russian Empire ; in the southern half of which all such erratics 
cease, and fine black slime (tchornoizem) takes their place. 
Wherever the recent accumulations of the steppes indicate the 
