GREAT JURASSIC BASIN OF THE LOWER VOLGA. 
243 
cow. Lastly, in reference to many other parts of the governments of Moscow, 
Vladimir, and the adjacent tracts 1 (in which, it is to be remarked, no trace of any 
cretaceous or tertiary fossil has yet been found), we venture to suggest, that nearly 
all the ferruginous sands with ironstone concretions will also be found to belong to 
the same member of the Jurassic series, — the youngest formation which has yet 
been proved to exist beneath the drift and recent accumulations of this central 
region. This conclusion is, we think, sustained by fair analogy, and by the fact, 
that all the Russian deposits preserve an uniform lithological character over very 
wide areas. 
Great Jurassic Basin of the Lower Volga, and of the Governments of Simbirsk, 
Tarnbof, and Saratof.— The Jurassic rocks of Russia, as already explained, occupy 
detached basins only, and are therefore of less continuous extension than the 
systems of Palaeozoic age. When viewed upon the map, these masses appear ot 
much less horizontal extension than even the cretaceous deposits which overlie 
them. This view, founded as it is upon the knowledge we at present possess, must 
not, however, be exaggerated. It is very true that in the tracts of the Middle 
Volga, the Oka, and theMoskwa already described, as well as in the isolated patch 
discovered by one of us near Sisolsk, to the north-east of Ustiug-veliki 2 , these 
deposits are narrow stripes of very limited extent. They resemble, in tact, detached 
relics of a sea, the deposits of which were probably separated by undulatory move- 
ments of the more ancient rocks. When, however, we follow the southern limit of 
the Permian strata from the banks of the Alatyr, south of Arzamas, to Simbirsk 
upon the Lower Volga 3 4 , or when we interrogate the deep denudations on the 
banks of that stream, to ascertain the nature of the base of the plateaux to the 
south of the governments of Simbirsk, Saratof and Penza, it is seen that every- 
where, from their northern boundary to Saratof, Jurassic rocks have extended 
and are visible beneath the cretaceous and tertiary deposits. To the south of Sa- 
ratof the great thickness of these overlying strata does not permit us to reach the 
Jurassic beds in any natural section, and their future prolongation in that direction 
1 We met with similar slightly coherent, ferruginous sandstones, in ravines on the right bank of the 
Oka at Piskavadi, between Mtzensk and Bielef, where they rest on the corroded surface of Devonian rocks. 
We may also state, that a proprietor of iron mines in the government of Vladimir informed Mr. Frears, that 
he had discovered Ammonites in the beds from which his iron ores are extracted. 
4 By Count Keyserling. (See Map.) 
» We designate as Lower Volga all the course of that river below Kazan. 
