408 
LOWER AND UPPER SILURIAN ROCKS. 
encrimte limestone, traversed by veins of quartz. These beds, having a north and 
south direction, cover the country to the point where the river Yegra-laga 
empties itself into the Uetsk ; and even in ascending the latter towards the north, 
they aie tia'ceable tor some distance. The only lithological variation observable 
in these beds, is when they pass into talc schist, and where they contain great flakes 
of mica. Their usual inclination is 80° towards the east, by which position it may 
be supposed that they are inverted, like certain strata before alluded to, which 
approach the Ural ridge on more southern parallels. 
In descending the river Iletsk, the same beds plunge westwards, and still present 
the same courses of fetid encrinite limestone, and apparently with no other fossils. 
Upon them rest thick masses of subcrystalline grey limestone (marble), occupying 
cliffs of about 400 feet above the stream. Though it is difficult to extract organic 
remains from this rock, we detected in it, besides turriculated, indeterminable shells 
(probably, like those of Nijny Tagilsk, of the genus Murchisonia) , the Pentamerus 
Ostiacus and the Calamopora alveolaris. The two last-mentioned fossils are indi- 
cative of Upper Silurian age, and as the rock rests upon the slaty schists with 
enciinite limestone, the latter, we inferred, must represent a portion of the Lower 
Silurian, like other masses to which we shall now advert. 
The upper or marble beds dip both to the east and west, at angles from 40° to 
near vertically, and form a great basin, from beneath the western side of which the 
same argillo-calcareous schists rise up, as on the east. In one locality near the river 
Jezem, these slaty schists constitute a rock, much resembling in lithological aspect 
that of the shelly portion of the mountain of Snowdon in North Wales, and like it 
containing true Lower Silurian species, such as Orthis calligramma (Dalm.). O. tes- 
tudinaria (Dalm.), O.inflexa (Pand.), Terebratula crispata (Sow.), T. pleurites, n s. 
Lepteena trama, n.s., a large indeterminable Orthoceratite, and the Calamopora 
fibrosa var. Sphcera. 
The occurrence of these shells in beds which underlie Upper Silurian rocks, 
and pass conformably into talcose and chloritic schists, is of great importance in 
leading us to believe, that by far the greater portion, if not the whole, of the Ural 
must originally have been formed of true palaeozoic deposits 1 . 
Still further to the west, Lower Silurian rocks with black encrinite limestone 
1 This Pentamerus, which is not to be found in Part III. of our work, will be figured and described by 
our colleague Count Keyserling, in a forthcoming publication, entitled " Reise in das Land dcr Petchora ” 
the plates and letter-press of which being of precisely the same size as our own, will form a natural sup- 
plement to this work. 
