PLEISTOCENE LOAMY DEPOSITS. 161 



and cause them to accumulate much sediment in their valleys ; 

 but we have no reason to believe that loss ever filled up the 

 valleys in the manner supposed. On the contrary, all the 

 evidence goes to show that the accumulation in question is a 

 mere superficial covering, spread over the surface of the ground, 

 the original features of which it disguises but does not conceal. 

 There is no proof that the Ehine valley was ever filled across 

 its whole breadth, and throughout its entire length, from Basel 

 say to its mouth, with a depth of 300 or 400 feet of loss. The 

 loss is a mere envelope which cloaks the slopes of the valleys, 

 and was probably never much thicker than it is now. More- 

 over, it is obvious that Lyell's theory will not account for the 

 presence of loss in valleys, the drainage of which could not 

 have been affected by any subsidence of the Alps. To explain 

 the occurrence of loss in such valleys we should on the same 

 principle be compelled to suppose that the Pyrenees, the 

 plateaux of Central France, the Vosges, the Thiiringer-Wald, 

 the Erz mountains, and the Carpathians, had likewise been 

 depressed with reference to the surrounding low grounds, and 

 again elevated. And a similar inference would be necessitated 

 for the limited and little elevated watersheds in the south of 

 England. Nor would all these local movements of subsidence 

 and re-elevation account for many considerable areas of loss, 

 amongst which I may mention that narrow zone which extends 

 in Northern Germany along the southern margin of the great 

 " Northern Drift." It is likewise obvious that we should still 

 have to account upon some other principle for the enormous 

 development of the black loamy deposits of southern Eussia. 



There is one opinion upon which geologists are pretty 

 generally agreed, namely, that the loss of the great valleys of 

 Central Europe consists for the most part of glacial mud. It is 

 believed to be the finely-levigated material derived from the 

 grinding of glaciers upon their rocky beds, and transported to 

 the low grounds by torrents and fluviatile action. And it is 

 likewise admitted by most that this distribution of fine silt took 

 place at a time when the mountain systems of our continent 



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