CHAPTER III. 
SILURIAN ROCKS OF RUSSIA. 
Introductory View of the prevalent physical Features of Russia in Europe. — Crystal- 
line Rocks to the North of the Silurian Zone. — Line of Elevation accompanied by 
eruptive Rocks and Fissures transverse to the Crystalline frontier of the North . — 
Consequent Obscuration of the Junction between the Azoic and Protozoic Rocks . — 
Silurian strata in the government of St. Petersburgh represent the Lower Group 
only. — Transverse sections of the same to the South of St. Petersburgh and on the 
rivers Ishora, Tosna, Volkof and Siass, showing that the Lower Silurian Rocks are 
there at once surmounted by strata of Devonian age. — Silurian Dislocations and 
Flexures accounted for. — The Lower Silurian beds of Esthonia and Kovno pass up- 
wards into Limestones with Pentameri, intermediate between the Lower and Upper 
Groups. — Upper Silurian Rocks developed in the Isles of Dago and Oesel. — Review 
of the characteristic Silurian Organic Remains, proving a division into Lower and 
Upper Zones in Russia, as in Norway and Sweden. (See Map, Table and Sec- 
tion, Plate VI.) 
As a prelude to the description of the geological structure of Russia, we must be 
permitted to say a few words upon the physical features and drainage of that 
great central portion of the empire, the exploration of which has been our main 
object. 
Bounded on the north by a vast country occupied by crystalline rocks, and 
surrounded on other sides by the mountains of the Ural, the Caucasus and the 
Carpathians, Russia in Europe maybe viewed as a spacious, low, undulating region, 
which opens out into the great depression of the Caspian Sea on the south-east, 
and to the flat countries of Northern Germany on the west. 
Considering its magnitude, this mass of land is very remarkable in being de- 
