CENTRAL BASTN OF CARBONIFEROUS LIMESTONE. 
77 
those upon the Dwina, and containing some of the same shells, with the corals 
Lithostrotion jloriforme and Harmodites parallelus, were observed by us to extend 
for a short distance up the river Pinega. The lower carboniferous strata are ob- 
scured on the banks of the Dwina, and we would recommend those who follow 
us, to descend the river Onega, which passes through a gorge, about seventy 
miles above the town of that name, and where a junction of the limestone and 
underlying Devonian rocks is said to be exposed. We adhere, however, to the 
belief before expressed, that the bituminous shale and sands and dark limestones 
thin out, and that the subformations of the system are not nearly so much deve- 
loped in their north-eastern range, as in the central regions of Russia, to the 
consideration of which we now return. 
Great Central Basin of Carboniferous Limestone. — By reference to the Map it will 
he seen, that from the Valdai Hills as a centre, the carboniferous limestone extends 
not only to the north-east, into the country we have been describing, but also 
by Moscow, and far to the south and south-east of that city. We know little from 
personal observation of the western side of this great mass, the boundaries of which 
are with difficulty defined, in consequence of the superficial detritus with which it 
is covered. On the east, however, we endeavoured to trace it in a tedious course 
by Tcherepovetz, Ustiujna, Mologa, Rybinsk and Yaroslavl, and having also made 
traverses across the governments of Vologda, Perm, &c., we are enabled to state, 
that no Carboniferous limestone appears in the wide area coloured red (No. 4) to 
the east of the Volga, until you reach the flanks of the Ural Mountains. 
Confining our remarks in the first instance to the lower division, we may state that 
our researches along the southern edges of the Moscow basin afforded us precisely 
the same results as in the Valdai Hills upon the north. In the zone of country 
extending from the north of Lichvin, on the west by Peremishel to Tula, the lower- 
most carboniferous strata, which succeed to the Devonian rocks, consist of sand 
and shale, w 7 ith thin coal-seams, which are immediately surmounted by a lime- 
stone with Productus giganteus. 
The thickness of the sand and sandstone varies in different places, and the thin 
courses of coal which are subordinate to them, vary considerably in quality and 
thickness in different localities. Thus at Jeleniena, noith of Lichvin, bands of 
poor coal appear in a ravine under the village, subordinate to bituminous schists, 
some of wffiich, like many similar beds in England, sound like wrnod under the 
hammer. Incoherent sands surmount the black mass, and sandy layers with stems 
M 
