404 
“very recent deposits, these grits are the youngest solid strata in the 
northern half of Russia in Europe. 
Chalk.—The cretaceous system is largely developed in the south, 
near Simbirsk, and in the Crimea; but on this occasion the authors 
did not extend their tour to the chalk districts. 
Tertiary Deposits._-The white shelly limestone of Crimea, and 
its relations to the underlying chalk, have already been described by 
one of the authors*. Such deposits have not yet been discovered 
in any of the northern or central regions of Russia. 
Post Pleiocene (Pleistocene).—It was formerly the general belief, 
that the great masses of superficial detritus, whether clays, sands or 
blocks, which cover so very large an area of the northern region, 
were all referable to one epoch (diluvian) in which the bones of 
great extinct quadrupeds were also imbedded. The duration of their 
journey was not sufficient to enable the authors to make many di- 
stinctions of age between these different masses; but they have 
commenced this division by the discovery of beds of clay and sand 
on the banks of the Dwina and Vaga, upwards of 200 miles south 
of the White Sea, which contain twenty-two species of shells, many 
of which still preserve their colours, and which, having been referred 
to Dr. Beck, of Copenhagen, have been pronounced by him to be all 
of modern northern species. Mr. Lyell states that they are identi- 
cal with the Uddevalla group described by him in Sweden. Mr. 
Smith adds, that these shells are nearly all the same as those which 
he has found in various ancient elevated sea bottoms around the 
coasts of Scotland. In referring twenty of these to modern arctic 
species, Mr. G. Sowerby doubts if a certain Mya has ever been found 
recent, and states that a Cardium, approaching to C. ciliatum, is dif- 
ferent from any northern form he is acquainted with, and near to 
certain Australian types. This discovery, in which they were assisted 
by Count Keyserling, who accompanied the authors in their tour to 
Archangel, is conceived to be of high geological interest, as it de- 
monstrates that, during the quasi modern period, the whole of the 
vast flat country of north-eastern Russia was beneath the sea for a 
considerable time, the eastern boundary of that sea being probably 
the slopes of the Ural Mountains. 
Drift and Erratic Blocks.—Overspreading all the formations, and 
greatly obscuring them, is a vast mass of detritus, the large granitic 
_ and other crystalline blocks of which have excited much attention, 
from the days of Pallas to the present time. This detritus, the blocks 
of which have all been derived from the north, is shown to have 
been deposited under the sea, or in other words, upon a sea bottom, 
since it covers the above-mentioned shells. 
Notwithstanding the obscuration occasioned by this wide-spread- 
ing drift, it is stated that the nature of the subsoil, or fundamental 
deposits, can often be surmised from the colour of the superficial 
clay and sand, and the materials of small detritus, the surface of the. 
Silurian zone being grey, that of the old red, red; whilst the cover 
of the carboniferous limestone is often charged with many broken 
* M. E. de Verneuil, 
