312 
[Chap. XIII. 
SILUKIA. 
on the west, the following succession is exhibited in ascending order in proceed- 
ing from the Silurian and Devonian rocks of the Ural chain : — Carboniferous 
The Gurmaya Hills of the South Ural Mountains. 
As seen from the Steppes of Orenburg. (From ' Eussia-in -Europe,' vol. i. p. 450.) 
Limestone, with the usual large Producti and other fossils, passing upwards into 
Carboniferous Flags with slight traces only of coal. These rocks are followed 
by the Permian group, consisting of : — 1. Sandstones and grits, limestones in 
various courses, with fossils of the Zechstein of Germany, associated with marls, 
gypsum, &c. ; 2. Red sands, with copper-ores and many Plants ; 3. Conglome- 
rate and sandstone, with fossil Plants and Reptiles. 
At the Imperial Baths of Sergiefsk, and on the banks of the River Sok, a 
tributary of the Lower Volga, magnesian limestone and marl contain gypsum, 
copper-ore, native sulphur, with sulphureous and asphaltic springs in the middle 
masses, whilst other marlstones and white limestones constitute the summit. 
A considerable volume of gaseous, sulphureous water, which forms a large pool, 
issues from these rocks. (See diagram, 1 Russia-in-Europe," vol. i. p. 158.) 
Near Kazan, about 150 miles to the north of Sergiefsk, huge masses of gypsum * 
(a), rising high above the level of the River Volga, are surmounted by limestone 
cliffs with Zechstein fossils (b), and the latter by red, green, and white marls 
(c), as here represented. 
W. Permian Deposits near Kazan. (From ' Eussia-in -Europe,' p. 162.) E. 
a. Thick deposit of gypsum, b. Limestone with well-known Zechstein fossils. 
c. Eed and green shelly marls, also with Zechstein types. 
* Cliffs of white gypsum, subordinate to the they form white cliffs for many miles, and again 
Permian rocks, are still more conspicuous on the near Pinega, where with my companions I ex- 
banks of the Dwina south of Archangel, where amined them in the year 1840. 
