160 PREHISTORIC EUROPE. 



ddhdcle passed ; a large proportion of the muddy contents of 

 the basin being carried far down the valley, and scattered over 

 a wide area. Another view, suggested by Giimbel in his great 

 work on the geology of Bavaria, endeavoured to account for the 

 loss by a rapid melting of the extensive snow-fields and glaciers 

 of the Alps, which was supposed to have taken place towards 

 the close of the Glacial Period of geologists, and to have been 

 induced by a sudden depression of the mountains. Vast volumes 

 of water thus set free, descending in irresistible torrents and 

 ddbdcles, strewed all the low grounds with sand and gravel, and 

 soon forming a wide inland sea, allowed the deposition of fine mud 

 (loss) to take place quietly and continuously. Sir Charles Lyell, 

 on the other hand, was of opinion that the loss had been de- 

 posited as a fine alluvial silt by the present rivers at a time 

 when their fall was considerably lessened by a gradual sub- 

 sidence of the Alps. Their power of transporting sediment 

 being thus reduced, much of the mud and silt which they 

 formerly carried to the sea was now allowed to accumulate in 

 the valleys themselves, and this process is supposed to have 

 continued until the rivers had deposited a thickness of several 

 hundred feet of loss — until, in short, wide valleys like that of 

 the Ehine above Bingen had become well-nigh filled up. The 

 Alps and the upper reaches of the valleys having become 

 subsequently re-elevated, the rivers re-excavated their loams, and 

 cleared out the basins which they had previously filled to 

 repletion. 



Each of the views now mentioned postulates the former occur- 

 rence of some movement of the earth's crust — a demand not in 

 itself unreasonable if it otherwise satisfies all the conditions of 

 the problem. But this is just what each of the theories fails to do. 

 The geographical distribution of the loss and its associated de- 

 posits, and the elevation often attained by them above the valleys 

 are fatal not only to every form of the lacustrine hypothesis, but 

 also to the ingenious view supported by Lyell. A depression of 

 the Alps and the surrounding regions would doubtless diminish 

 the fall of the rivers that take their rise in those mountains, 



