THE GLACIAL PERIOD. 



243 



Jurassic shale contains a large amount of bituminous matter, 

 which would account reasonably enough for the considerable 

 percentage of organic substance met with in the black- earth. It 

 is not improbable, however, that here and there the blackness of 

 the earth may have arisen from the decomposition of grasses 

 and other plants. But if this were so, it is strange that traces 

 of vegetable dforis should appear to be so completely absent 

 from the deposit. The absence of plant-remains, however, is 

 quite in keeping with the non-appearance of shells or animal 

 relics of any kind, and is readily explicable on the theory of the 

 aqueo-glacial origin of the black-earth. It is hardly likely 

 that either plant- or animal-life would be well represented in 

 those low-lying regions of Southern Eussia which were liable to 

 be more or less completely inundated every spring and summer, 

 and which in winter must have experienced an excessively cold 

 climate. 



The black -earth would appear never to reach the great 

 thickness attained by the loss of the Ehine and the Danube. 

 This is what we might have expected from the configuration 

 and position of the regions over which it is distributed. The 

 wide open valleys and broad plateaux would not permit of the 

 same heaping-up and ponding-back of the flood-waters as must 

 have taken place again and again in Central Europe. The 

 route to the south lay open, and the inundation-waters would 

 thus be drawn off more rapidly than if they had been discharged 

 in a northerly direction, where the outflow was impeded not 

 only by the presence of glacier-ice, but by the freezing-over of 

 the rivers themselves. 



Some geologists have suggested a marine origin for the 

 black-earth, but no one has ever succeeded in discovering in 

 this deposit a single trace of any marine organism. And those 

 who hold that the Northern Drift with its large erratics has 

 been transported southwards by means of icebergs and currents 

 are equally at a loss to account for the sudden disappearance 

 of boulders not far from the northern limits of the Steppes. 

 If icebergs during the Glacial Period sailed over the watersheds 



