130 Mr. Murchison on the Geological Structure 



surface, the strata in their proximity are highly altered. Thus even 

 when studied on a small scale on the western flank of the moun- 

 tains, as at the baths of the Zavod of Sergiefsk, the sandstone in 

 contact is altered into quartz rock, and the limestone, so regularly 

 bedded and full of fossils at a little distance, is converted into an 

 amorphous, crystalline, splintery mass, charged with cross veins, and 

 sulphureous saline waters flow from its base, the adjacent rocks 

 being also much impregnated with iron ore. Similar but on a far 

 grander scale are the phenomena of intrusion and metamorphism 

 which are presented by the central axis of the Ural, and to a less 

 extent by all the parallel ridges which flank it on the eastern or 

 Siberian side. 



The Ural-tau or crest is to a very great extent a wall of schist 

 and quartz rock diversified by points of igneous rocks, and though 

 of no great altitude, it is very remarkable that throughout 17 de- 

 grees of latitude this water-shed is not broken through by any great 

 transverse valley. The Ural-tau marks, in fact, one long line or 

 fissure of eruption. With the exception of the gold mines near 

 Bissersk, on its west flank, all the gold alluvia of the chain occur 

 on its eastern flank ; and when it is stated that this circumstance is 

 connected with the fact, that all the great masses of igneous rocks 

 have been evolved on the eastern flank, it will at once be seen (as 

 insisted upon so well by Humboldt) that there is an intimate con- 

 nexion between the eruption of plutonic rocks and the formation of 

 the gold mines [veins ?] whence the local alluvia have been derived. 

 That this connexion exists in regard to other mineral veins, is also 

 equally apparent in the Ural mountains ; for with very rare excep- 

 tions, it is only on their eastern or eruptive side that copper veins, 

 malachite, platinum and magnetic iron prevail*. 



Without entering into all the lithological distinctions of the North 

 Ural, they advert specially to the occurrence in the districts of 

 Turinsk and Nijny Tagilsk of a stratified and regularly bedded por- 

 phyry, which they compare with the " Schaalstein" of German geo- 

 logists, and which on the banks of the Kakwa and east of Bogos- 

 lofskf , as in the Rhenish provinces, alternates with limestone strata 

 of Devonian age. In the copper mines of Turinsk, the veins and 

 masses of ore are shown to be intimately connected with the intrusion 

 of greenstone, between a thick mass of which and the metalliferous 

 veins is a garnet rock. This phenomenon is a counterpart to that 

 formerly described by Professor Henslow in the Isle of Anglesea ; 

 whilst on the river Kakwa, the ordinary limestone (Devonian?) has 

 been converted by a dyke of greenstone into white granular marble, 

 in the same way as by the contact of syenite the lias limestone of 

 the Isle of Sky has been changed. 



The Katch-kanar mountain (lat. 58° 44-'), which the authors vi- 

 sited by a little-frequented pass, is composed of augitic greenstone 



* In sketching the chief relations of the plutonic and metamorphic rocks 

 of the North Ural, much praise is given to a detailed geological map of the 

 environs of Bogoslofsk by Capt. Karpiuski, of the School of Mines, with a 

 copy of which the authors were furnished. 



t See Geol. Trans, vol. vi. pp. 246, 248. 



