CHAPTER IV. 
DEVONIAN, OR OLD RED SYSTEM. 
Great extension of the System . — Described in ascending order, from the junction of its 
lower strata with the Silurian rocks of the Volkof, to the contact of its upper beds 
with the Carboniferous Limestone in the Valdai Hills. — Range to Vitegra, Andoma, 
and Archangel. — Range and contents in Courland, Livonia, Sc. — Great South- 
eastern band extending to the Governments of Orel and Voroneje, and sections of it 
on the rivers Oka and Don. — Organic Remains of the System in Russia compared 
with those of Western Europe. 
The red rocks which lie to the south of the Silurian strata of the Baltic con- 
stitute one of the largest systems of Russia l , and extend over an area of not less 
than 150,000 square miles : — a region much more spacious than the British Isles. 
Reposing upon the low plateaus which have just been described, and rising into 
hills, varying from five hundred to upwards of nine hundred feet above the sea, 
this zone is well defined both at its lower and upper limits ; for it passes down into 
beds of Silurian flagstone and is surmounted by true carboniferous limestone. 
Thus, occupying the same geological horizon as the Old Red or Devonian system 
of Great Britain, these rocks form the substratum of Courland and of Livonia, 
from whence they range north-eastwards into the governments of Pskof, Novo- 
gorod, Olonetz and Archangel, and south-eastwards through Vitebsk, Smolensk, 
Kaluga and Tula, to Orel and Voroneje. We shall first describe these deposits 
in their north-eastern and afterwards in their south-eastern range. 
Northern Devonian Zone. — With the exception of certain summits of carboni- 
ferous limestone, the Valdai Hills, and all the hilly region around Lake Ilmen, 
are composed of Devonian rocks. On the sides of the high road from St. Peters- 
1 See Map, Tabular View and Section annexed to it. 
