270 
CRETACEOUS ROCKS OF THE DON. 
Whatever horizon may hereafter be assigned to the uppermost sands, or (e) of 
this section, we can have no hesitation in considering the three underlying mem- 
bers as Cretaceous, and from their stratigraphical and lithological connection we 
believe them to he also part of the same system ; their composition and re- 
lations have also convinced us, that the strata over wide surfaces to the east and 
south of Kursk, of which they are prolongations, may owe their paucity or absence 
of organic remains to the lithological composition of the rocks. It is, indeed, 
certain, that with the exception of containing a little calcareous matter, the argillo- 
siliceous marls of Kursk, are identical in colour, aspect, composition and manner 
of bedding, with the white siliceous clay-stones of Kharkof, and the formation is 
continuous between these places. 
The establishment, therefore, of the age of the marls of Kursk by their inter- 
lacement and connection with white chalk, ironsand and greensand containing 
fossils, is a point of considerable importance, in clearing up the obscure question, 
as to what is or is not to be included in the Cretaceous system of Russia. Major 
Blode, who had closely defined the lithological character of these strata in the 
government of Kharkof, not having, when we left the country, seen the proofs w r e 
discovered at Kursk, was unable, from zoological or other evidence, to assign such 
beds to their correct place in the series ; but we must do him the justice to say, 
that arguing from their aspect and composition, as well as from the entire absence 
of tertiary fossils (which, he contended, if the deposit were younger than the chalk, 
would be found in them), he always considered the strata around Kharkof as be- 
longing to the secondary rocks. 
Cretaceous Rocks of the Don . — On referring to the Map, it will be seen that cre- 
taceous rocks occupy very wide spaces upon the Don. These masses may, indeed, 
be considered as the eastern prolongation of the deposits in Southern Russia, to 
which we have just adverted. 
In passing from the Donetz to the Don, and particularly on the banks of the 
Kalitva, we found sections, in ascending order, analogous to those of Kursk, from 
white chalk, through whitish marls and “ Kiesel-thon ” to siliceous sand. The 
same order is seen on the left bank of the Don at the station of Matiushenskaya. 
Again, much further down that stream, below the great elbow which it makes 
towards the Volga, we met with a similar succession between Golabinskaya and 
Piattisbianskaya, to the south and east of which last place the white chalk with its 
superincumbent and associated marls, marlstone and sandstone sinks beneath the 
