or Black Earth of Russia. 135 



Unlike all great regions hitherto examined^ central Russia is 

 void of rocks of igneous origin or intrusive character^ and all her 

 strata deviate from horizontality only by the slightest undulations. 

 From this fact and from the incoherent texture of the rocks it is 

 clear that her subsoil, which on account of its marine contents we 

 know to have been formed under the sea, must have been raised 

 and desiccated by very gradual and even movements. Judging 

 from the evidences of geological succession also^, and seeing that, 

 without the aid of great fractures or dislocations in the crust of 

 the earth, some of the older rocks of Russia, such as the moun- 

 tain limestone, are covered conformably by the inferior oolite, 

 whilst the lias and, to a great extent, the new red sandstone are 

 wanting, we see in these facts the proofs that either the former 

 bottom of the sea was raised above the waters and remained dry 

 for long periods, or that, in this very tranquil region of the earth's 

 surface, the absence of all widely-spreading powerful currents 

 ceased, at intervals, to extend from the neighbouring seas and 

 rivers. Pursuing this mode of reasoning from the more ancient 

 phenomena to those which immediately preceded our own era, we 

 are led by positive evidence to conclude that the whole surface of 

 central Russia (however parts of it may have had formerly di- 

 viding barriers) was during that period again depressed beneath 

 the level of the sea, in which the marine shells of the government 

 of Archangel and the Southern Steppes were accumulated, and 

 over which the sand, clavj, pebbles, and blocks of the north, as 

 we have before described, were deposited. 



In all those parts where the strata show no signs of dislocation, 

 the present physical features of the country, indeed, serve to 

 explain the outline of the southern edge or extreme range of the 

 northern drift ; for where high plateaux, like those on the left 

 bank of the Volga between Nijny Novogorod and Kasan, stand 

 out with their cliffs to the north, there we trace a well-defined limit 

 beyond which that drift has not proceeded ; and where, on the 

 contrary, longitudinal valleys, like that of the Okka, open to the 

 south, there we perceive that northern blocks have advanced from 

 50 to 150 miles farther. In no part, however, of the great 

 northern region occupied by the northern drift is there a trace of 

 the " Tchornoi Zem," though yellow and white sands and stiff 

 clays abound, the latter constantly charged with transported 

 pebbles like our English drift or diluvium. 



Extending then as far southwards as currents, icebergs, and 

 other causes, to which I have formerly referred, would transport 

 them, and a submarine outline would permit the materials to 

 advance, it is very natural to suppose that, where the northern 

 drift ceased to advance, the bottom of the then sea, far removed 

 from any currents, or unagitated by any disturbing force, would 



