JURASSIC STRATA BETWEEN THE URAL AND THE TIMAN. 
417 
that they must be of higher antiquity than the portion of the Lower Silurian rocks 
which we have shown to exist on the western flanks of the Arctic Ural, and which 
there succeed conformably to true Upper Silurian rocks. 
Jurassic Rocks between the Arctic Ural and the Timan Range. In the great hollow 
in the earth’s surface formed hy the elevation of the rocks which we have been 
describing, or, in other words, in the great basin between the Ural and the Timan, 
no other deposits are visible save Jurassic shales, which are filled with many ot the 
same organic remains as those which have been brought to light in other parts ot 
Russia, and these are partially overlaid by very modern marine accumulations 1 . 
The same species of Belemnites, the same small Aviculse and the same Inocerami 
abound in the region inhabited only by Samoyedes, which we traversed towards the 
mouth of the Petchora ; and the same fossils have been brought by M. Ruprecht, 
the botanist, from the argillaceous portions of the more northern peninsula called 
Kanin-nos. 
The best section of these Jurassic beds with which we became acquainted, is 
exposed on the banks of the river Ijema, or Ishma. At its confluence with the 
Petchora, large masses of a grey calcareous grit or sandstone, with a yellowish 
surface, and subordinate to the clays, are charged with Ammonites and other 
shells, as well as fossil wood. Beneath these succeed clays of very great thickness, 
with little concretions of cement, stone or argillaceous limestone, and still nearer 
the base is a shale similar to that of Goroditche and Moscow, in which are inter- 
laced many Posidonias, the whole reposing upon Devonian limestones. Some 
hard bands in these Jurassic shales, which we did not meet with in other parts of 
these regions, cause dangerous rapids on the rivers Ishma and Vim. The banks of 
the river Sisola, and of its affluent the Visinga, must, however, be cited as good 
Jurassic localities, not only because they have afforded a multitude ot Oxfordian 
fossil shells, but also the rib of a great Saurian. Whether this bone may belong 
to the same Plesiosaurus, the vertebra of which have been recently found 2 in beds 
of the same age near Moscow, is more than we can pretend to determine. We can 
here only dwell on the interesting fact, that although examined for so very short 
* See account of these Jurassic tracts, p. 230, and of the ternary depots of the Petchor , p^ 332. 
• Having submitted a cast of one of these vertebr* and half of one of the ongmals found by M, Frears 
to Professor Owen, his opinion is thus expressed The Moscow vertebne belong to tbe Ple.osaurus 
. , , , N T, .. c Tj Association 1839, p. 78. 1 hev are both middle cervicals, 
brachyspondylus (Owen), Report of British Associati , l ' „ 
equalling in size our ordinary English specimen from the Kimmeridge and Oxford clays. 
