745 
colour and suberystalline aspect, those of South Devon in England, 
and they contain fossils characteristic of this division both in the 
British Isles, in Belgium, Prussia and the Eifel ; but though perfectly 
identified both by position and contents with the Devonian rocks of 
the flat regions of Russia, the Uralian strata are as dissimilar from 
them in external aspect as the rocks of the same age in Devonshire 
are from the old red sandstone of the north of Scotland and of 
Herefordshire or Brecon in England. Nor are these Devonian rocks 
on the western flanks of the Ural separated from the lower car- 
boniferous limestone by any band of sandstone and coal as in the 
northern parts of Russia in Europe, but the grey limestone of the 
overlying group is at once succeeded by the dark limestone of the 
other, both undergoing the same flexures, and both forming parts 
of one great paleozoic series. 
In their prolongation to the south, the limestones of this Devo- 
nian group thin out and inosculate with a considerable development. 
of red sandstone, grit, fine conglomerate and schist, in some parts 
resembling the old red sandstone of the Highlands. A peculiar 
mineral character of these Devonian limestones is, that they retain 
their black colour even when in the state of dolomite. 
Stlurtan Rocks.—-The schists and flagstones which underlie these 
limestones are considered to be of Silurian age ; with these strata 
are associated beds of limestone for the most part concretionary, 
and which are well developed on the banks of the Serebrianka from 
the zavod of Serebriansk to near its mouth. Among the predomi- 
nant fossils of this group and amid numerous corals, the Terebratula 
prisca ( Atrypa affinis, Sil. Syst.) is clustered together in great masses, 
as in the Ludlow rocks of England, and with it are associated the 
remarkable Leptena Uralensis and other new species. ‘The same 
descending sequence cannot be so well seen in many parts of the 
North Ural, as on the banks of the Serebrianka. 
Immediately, however, to the east of the water-shed (viz. from 
Bogoslofsk to Nijny Tagilsk and Neviansk), broken masses of 
limestone, insulated amid plutonic rocks, are charged with large 
Pentameri, closely approaching to the Pentamerus Knighta of 
the upper Silurian rocks, and associated with Orthis, Terebratula 
and other fossils, which, from collections sent to him, M. de Buch 
has classed as Silurian forms (see Beitrage der Geb. Form. in Russ- 
land. Von L. Von Buch. 1840). Although then the clear strati- 
graphical sequence is interrupted, there is no doubt that the equi- 
valents, at least of the upper members of the Silurian rocks, exist 
in these mountains; and in tracing such into the South Ural, par- 
ticularly by a transverse section from Verch-Uralsk to Sterlitamak, 
the authors convinced themselves, from the presence of Orthide, 
Pentameri, &c., that where not much interfered with by intrusive 
rocks, the central deposits of the chain (usually however in the 
state of slate and quartz rock) belong to the Silurian system, and 
probably to its lowest divisions. 
The symmetry which is developed on the western side of the 
water-shed is almost obliterated to the east by the greater frequency 
