DEVONIAN LIMESTONES ON THE TCHUSSOVAYA. 
385 
reous Devonian rocks which are near the mouth of the Serebrianka, also occupy 
the cliffs of the Tchussovaya near the union of these rivei's. It is useless to 
describe in detail all the reversals of dip or flexures of the various black and 
schistose limestones, marked by irregular white veins, which alternate with thin- 
bedded black chert or flint. The bends and breaks of these limestones are indeed 
quite as numerous and as remarkable as those of the grauwacke sandstone and 
schists upon the Serebrianka. There are, however, lithological varieties a little 
below Ust-Serebriansk which x’equire notice. These are saccharoid dolomites, 
both white and black, which, here and there, are detected amid the convoluted and 
partially altered limestone strata. The black dolomite (a rock unknown we believe 
in Western Europe) is occasionally seen in very thin beds, perfectly interstratified 
with the ordinary subcrystalline limestone, and in highly inclined positions. The 
white dolomite occurs at a point of great disturbance, and where the dip is reversed. 
By reference to the Map it will be seen, that these dolomites, which range along 
the great north and south fissure of the Tchussovaya, lie between two lines of 
igneous eruption, one of which has been already noticed at the mineral springs of 
Sergiefsk ; the other (it will he subsequently mentioned) ranges northwards from 
Bissersk, a tract in which black dolomite also largely occurs. 
After various undulations, in which masses of limestone many hundred feet in 
thickness, occasionally highly fetid and containing bands of dolomite, are arched 
over grauwacke grits, these Devonian rocks, for the most part inverted or dipping 
towards the Ural chain, though in other places away from it, are again most instruct- 
ively exhibited in regular sequence, at the Kinovski Zavod, on the left bank of the 
Tchussovaya. Here a transverse ravine exposes the following section in ascending 
order from the western buildings to the edge of the stream, the whole dipping 
about 50° to the east. 1. Strong-bedded grey limestone, with Terebratula prisca. 
2. Black beds with geodes and concretions of chert. 3. Dolomitic sandy lime- 
stone, followed by courses of clay and thin flat beds of white dolomite, the whole 
covered by impure limestone passing into quartzose calcareous grit. These rocks 
are Devonian ; for they contain Terebratula reticularis (prisca), Spirifer Murchi- 
sonianus (De Kon.), with Favosites spongites, F. polymorpha, Stromatopora concen- 
trica, Lithodendron ccespitosum, and Caunopora favosa, &c. 
By this high inclination of the strata at Kinovsk on the west, and that of simi- 
lar strata towards Oslankoi Pristan on the east, a vast trough is formed, in which 
appears a great mass of amorphous light-coloured limestone, called by the Russians 
