370 
ROCKS OF NIJNY TAGILSK. 
our brief survey of Nijny Tagilsk, particularly in reference to the structure of the 
adjacent ridge of the Ural, which we did not visit, though we traversed it on two 
parallels further to the north. 
The chief features which arrested our attention here were, first, the geological 
age of the strata ; secondly, the chief metamorphoses they had undergone, and the 
agencies by which such changes had been effected. 
Like many other Zavods along the eastern flank of the Ural, Nijny Tagilsk is 
situated amid low hills of eruptive rocks with interjacent masses of sedimentary 
strata, most of which have undergone great alteration, and which usually have a 
crystalline or sub-crystalline character. The junctions of these two classes of rock 
or their immediate neighbourhood, are the seats of the chief veins and masses of 
mineral ore which render this locality so productive ; whilst alluvia with gold and 
platinum choke up some of the adjacent transverse valleys that radiate from the 
central mountains. 
Notwithstanding the numerous points of eruptive rocks (for the most part horn- 
blendic greenstone or amphibolite), and the great diffusion of altered rocks in their 
vicinity, patches of limestone are wedged in at intervals, which not having under- 
gone much change, contain sufficient organic remains to enable us to say, that the 
rocks in which they occur are of Upper Silurian age. This limestone, which is 
both of dark grey and whitish or cream colours, according to the lesser or greater 
amount of alteration it has undergone, contains a Pentamerus closely allied to if 
not identical with P. Vogulicus, a turriculated shell which can scarcely be distin- 
guished from the Gothland species Murchisonia cingulata ( Turritella , Hisinger), 
and a fragment which we refer to the Orthoceratites calamiteus (Miinst). 
Magnetic iron and its relations. — The limestones above-mentioned appear to 
have been rent in twain by a narrow ridge or wedge of intrusive hornblendic rock 
(greenstone), which extending from the Zavod to the north, rises into the \isso- 
kaya-gora or high hill, on the summit and flanks ol which magnetic iron ore has 
long been extracted. From the short time we employed in the examination ot this 
magnetic rock we cannot pretend to offer a satisfactory explanation ot the relation 
of the iron ore to the adjacent greenstone 1 . We may, however, add a slight con- 
tribution to what has been already published, particularly as the mines were much 
1 Hermann, who first described these rocks, speaks of this trappsean ridge as barren (of mines) 
“ taube,” — -a sort of porphyry passing to jasper, and containing white felspar and a little quartz. Miner. 
Beschr. des Ural, b. i. ss. 306, 309, 312. Rose did not examine this rock, but adds, that from the ana- 
'ogy of other rocks of magnetic iron, and what has been written concerning them, it is probably an augite 
porphyry with Labrador. Reise, vol. i. p. 311. 
