174 
ZECHSTEIN OF UST-VAGA. 
in the same position in relation to the carboniferous rocks, as the great masses 
described in the last chapter, which flank the Ural Mountains. The following 
woodcut will convey an adequate idea of how these gypsiferous beds (6) overlying 
the carboniferous limestone (a) pass under other beds of the Permian system (c 
and d). The gypsum is occasionally seen to assume large concretionary forms, 
which rise up and cut in dyke-shapes through the horizontal layers. Hie layer of 
limestone in the centre of the cliff, though often not exceeding a loot in thickness, 
is very persistent, and is marked by containing one or two peculiar fossils, the casts 
of which are sometimes occupied with a pellicle of green earth. The shells are, 
for the most part, Avicuke. These calcareous and gypseous courses are associated 
with and dip under red and green marls (c), which entirely occupy the banks higher 
up the stream, and on the Pianda, a western tributary of the Dwina, we found 
other small flattened concretions of pink-coloured gypsum, subordinate to spotted 
marls and a thick red soft sandstone. 
29 . 
N Section of the Dwina. Ust-Vaga. S. 
a 0 c d 
On the Dwina, near Schestozerskaya (where w T e first discovered overlying mo- 
dern sea-shells hereafter to be described) , the lower mass consisted of bands of 
gypsum, coloured by red marls, with white and pure thick-bedded gypsum. 
Still further to the south, other white limestones reappear, and these contain the 
same small Aviculee as lower down the Dwina, with other shells, and finally an- 
other limestone id) succeeds, which is exposed both at Shidrova on the Dwina, 
five versts below the mouth of the Vaga, and also on the south bank of that river 
immediately beyond the ferry. 
The strata near the water’s edge at Ust-Vaga, consist of impure sandy lime- 
stone, in parts almost a dingy, dark green calcareous sandstone, not much 
unlike some varieties of the Lower Greensand, covered by beds of dirty grey 
limestone, loaded with the following fossils, viz. Productus horrescens (nob.), 
Terebratula Schlotheimii '? (Buch.), Calamopora fibrosa, \ ar. ramosa, all of which 
belong to the true Zechstein division of the Permian system 1 . Independent, there- 
fore, of the inference, d priori, that in ascending the Dwina to higher lands, we 
necessarily reach newer strata, it is clear that from the moment we quitted the 
1 We shall afterwards show how these ancient limestones are covered by bands of blue clay, sands and 
gravel, with existing species of shells of Arctic character, like those at Schestozerskaya. 
