232 
SECTIONS ON THE VOLGA — PLES TO JURIAVETZ. 
Seeing (in 1840) the conformable junction of these dark-coloured strata with the 
inferior red beds at Pies, and thinking, when on the spot, that one of the Gryphae 
was not the G. dilatata , but rather the G. MacCullochii of the Lias, we were then 
disposed to believe, that these strata might represent both the Keuper and Lias. 
We mention this fact to show how extremely difficult it is to decide from an iso- 
lated case and one or two fossils, upon what may be termed conformity of suc- 
cession, particularly in a country where the strata are apparently horizontal, and 
are to a great extent unsolidified. In all those tracts, indeed, where the oscilla- 
tions of the land have been of such a nature as to leave the strata in positions 
more or less horizontal, it is evident, that the observer cannot expect to detect 
much appearance of unconformity in the planes or surfaces of any strata which 
happen to be in collocation, even though they have been deposited at very different 
epochs. When such junctions, however, occur, he may reasonably look for the 
effects of abrasion on the lower of the two sets of dissociated strata, whether 
by the action of former waters, or by other denudations to which the earlier beds 
were subjected before the succeeding strata were accumulated. We did not, in- 
deed, descend the Volga from Pies by Kineshma to Juriavetz, without observing 
decided proofs of such a condition of things. We found, in fact, that instead 
of occupying a regular overlying platform, the Ammonite and Belemnite shales, 
of whose exact age we were at first in doubt, occurred at different levels, some- 
times on the higher part of the cliff, at other places in depressions, and even de- 
scending beneath the waters of the stream, as represented in this woodcut, in 
which a marks the underlying red strata, b the Jurassic beds, and x the general 
cover of drift. 
34 . 
a 
We saw therefore, in the general contour of these shales and the various strata 
of red marl and sand on which they repose, exactly the same relations as those 
which occur, between the beds containing the same fossils near Moscow, and the 
carboniferous limestone upon which they there lie. In fact, the woodcut which 
has already been given, p. 80, explains a similar case ; though the underlying rocks 
at Moscow are of older age than those upon the Volga. The Ammonite and 
This woodcut relates to about thirty miles of country in horizontal extension. 
