242 PREHISTORIC EUROPE. 



more or less rapidly, and thus add their quota to the vast 

 volumes of water that poured southwards from the terminal 

 front of the ice-sheet. 



Now it is precisely in the low-lying regions of Southern 

 Eussia that we encounter the most extensive deposits of loam 

 in Europe. They form the subsoils of the Steppes — those vast 

 grassy plains which, within the drainage-area of the Don, the 

 Dnieper, and the Volga, comprise nearly 200 millions of acres. 

 The soil is generally a more or less rich dark or black loam 

 which yields heavy crops when it is cultivated, and which 

 would no doubt support an abundant forest- vegetation were it 

 not for the great droughts of summer, which scorch the ground 

 and forbid the approach of trees ; the principal vegetation of 

 the Steppes, in short, consists of grasses which often grow to a 

 height of five or six feet. 



Murchison and his colleagues, in their great work on the 

 geology of Eussia, were of opinion that the black-earth of the 

 Steppes may have been to some extent "derived from the 

 destruction of the black Jurassic shale, so uniform in its colour 

 over all Northern and Central Eussia." They also pointed out, 

 in proof of the correctness of this inference, the suggestive fact 

 that the black-earth is absent to the south of certain tracts 

 where there is reason to think the black Jurassic shale never 

 existed. " In truth," they remark, " the black-earth is in this 

 respect exactly like the Northern Drift of Eussia, which invari- 

 ably contains many materials of the formation immediately 

 north of it." According to the same authors it is wholly 

 unfossiliferous, but chemical analyses show that it contains 

 organic matter and traces of humic acid. Goebel states that he 

 detected vegetable debris in the black-earth, but the specimens 

 examined by him appear to have been taken from the surface, 

 which may also account for the quantity of carbonate of lime 

 found by him — a substance which, according to other analyses, 

 would appear usually to be wanting in the black - earth. 

 Bischoff is of opinion that the view held by Murchison and his 

 associates is very probably correct, inasmuch as the black 



