376 
ENVIRONS OF NIJNY TAGILSK. 
ties’, the collection alone which had been brought from them to Nijny Tagilsk 
sufficed to lead us to believe, that all the surrounding limestones were either like 
the Pentamerus limestone of which we have spoken as of Upper Silurian age or 
the oldest part ol the Devonian. This inference applies, however, to the compara- 
tively narrow tract only in which the chief mining works of the Demidoff family 
are situated. On its west rise up great igneous and metamorphic masses, which 
constitute the crest of the mountains, and sepai'ate the region in question from the 
palaeozoic unaltered deposits on the Tchussovaya and its affluents. 
To the east of Nijny Tagilsk and also within the Demidoff lands, lies another 
and much broader metalliferous tract, which differs from any zone upon the west, 
in being essentially granitic, though amidst it are other low ridges of syenite, 
greenstone and serpentine, all trending from north to south. Amid these intrusive 
rocks palaeozoic limestones occur at intervals, and are often highly altered. In 
one specimen, however, we detected the Chretetes radians, a true carboniferous 
coral, which led us to suppose that this eastern tract might be viewed as a pro- 
longation to the north of the palaeozoic group we have described in the same parallel 
of longitude upon the river Issetz, where it is also associated with granitic, por- 
phyritic and metamorphic rocks, the whole of which subside gradually into the 
plains of Siberia, -where they are overlapped by tertiary accumulations (see p.366). 
P .S. After these chapters were written, our friend M. Le Play, the able mineral surveyor and metallurgist 
of whom we have already spoken in relation to the coal country of the Donetz, was sent by M. Anatole 
Demidoff to examine his Uralian mines. We had great pleasure in furnishing this gentleman with a copy 
(not then finished) of our general geological Map of Russia and the Ural, and particularly requested him 
to employ his leisure moments in verifying or correcting the observations we had made. Whilst these 
sheets were going through the press, M.Le Play addressed a letter to Mr. Murchison, which, in addition 
to some remarks concerning the different ages of the eruptive rocks, the limits of the unaltered palaeozoic 
deposits on the Tchussovaya, and those of the more crystalline limestones around Nijny Tagilsk, contains 
a very clear account of the real nature and origin of the magnetic iron ore of these mountains. We are 
very glad to perceive that, both in the letter to ourselves, and in the one addressed to M. Elie de Beaumont, 
1 From the collections made at Nijny Tagilsk we recognized the Pentamerus limestone at the follow- 
ing localities : — Leba, and other places between it and Tchornoi Istostchinsk : Laisk, eighteen versts north 
of Nijny Tagilsk, where the Favosites polymorphus, Stromatopora concentrica, and stems of Cupresso cri- 
nites having been found, render it probable that the limestone there is Devonian. Again, at Vissimo- 
shaitansk, near to which platinum alluvia have been described by Humboldt and Rose, and which, though 
in direct communication with and dependent upon Nijny Tagilsk, is on the western slope of the axis, 
Pentameri occur in a black dolomitic limestone mineralogically undistinguishable from rocks upon the 
Tchussovaya, which will be spoken of hereafter as Devonian. 
