366 Geology of Russia and Australia. 
the mountains which separate it from Siberia. Over a vast area 
in Russia, except in the country along the Donetz, the older rocks, 
which are very loosely aggregated and crumbling, occupy a hori¬ 
zontal position, and have undergone very little metamorphic change 
or elevation. On the contrary, in the Ural the most violent dislo¬ 
cations have tilted, folded, and reversed the palaeozoic formations. 
The limestones are indurated and discoloured ; clays and friable 
sandstones give place to argillaceous schists and greywacke, and 
are only traceable by their fossil contents. 
In Scandinavia, which necessarily enters into comparison with 
Russia, the lowest Silurian rocks repose on gneiss or the more 
ancient schists which are denominated azoic, from the destitution 
of organic remains, the lowest Silurians being unconformably 
superimposed, and designated by Professor Sedgewick protozoic. 
The Silurian system, as developed in Sweden and Russia, is 
naturally divided into two periods geologically distinguished. The 
inferior ranges upwards to the calcareous rocks of Gothland ; the 
superior, which is not greatly developed in Russia, save in the 
Ural, embraces the Gothland rocks, which are the representatives 
of the English Wenlock and Ludlow beds. 
Near St. Petersburgh the Devonian system, charged with its 
peculiar fishes, many identical with those of the old red sandstone 
of Scotland, and associated with mollusca analogous to those of 
the Devonians on the Rhine, the rocks of which latter country 
also bear fishes identical with some in Russia, succeed to the 
inferior division of the Silurian system. 
The Devonian formations are enormously developed in Russia. 
It separates the carboniferous formation of Donetz from that of 
central Russia, and reaches towards the Teman Mountains and the 
Frozen Ocean, presenting in these far northern regions the same 
character it has on the Baltic and in the province of Valdai. I n 
the Ural Mountains its type is different. Its epochs are distinctly 
two; the upper beds consist of red marl, enclosing fish, and the 
lower of limestones bearing goniatites, and underlaid by schists 
analogous to those of Nassau and the Hartz. 
The carboniferous formation consists also of two natural divi¬ 
sions. In the north and centre of the country it is composed of 
