THE GLACIAL PERIOD. 233 



in all the great valleys that hold communication with snow- 

 covered mountain-regions, and not only so, but that vast quan- 

 tities of muddy deposits should be met with in places where 

 the form of the ground is such as would admit of quiet deposition 

 from inundating waters. Those great deposits of loss which 

 cover such extensive areas and reach to such heights in the 

 valleys of the Garonne, the Ehone, the Saone, the Seine, the 

 Rhine, the Danube, the Theiss, the Drave, the Save, and other 

 rivers flowing from the mountains of Central and Southern 

 Europe, represent the mud borne down by the great inundating 

 waters that escaped from the ancient glaciers. But the accumu- 

 lations which are known under the general terms of loss, lehm, 

 brick-earth, etc., have not all been formed in the same way. 

 Some are the result of mere subaerial waste — others have arisen 

 from the chemical action of acidulated water upon Cretaceous 

 strata — and superficial beds like these must frequently have 

 been re-arranged, redistributed, and often washed down from 

 higher to lower levels by rain and melting snow. It is not 

 necessary, therefore, to suppose that every high-level accumula- 

 tion of loam, silt, or clay, such as much of the brick-earth of 

 Northern France, is of fluviatile origin. The severe winter 

 frosts of the Glacial Period would penetrate some depth into the 

 ground, and tend to disintegrate the rocks and render these 

 more easily assailable by rain and melting snow. During spring 

 and summer much water would be set free, and quantities of 

 silt and loam would be transported down the slopes to accumu- 

 late in the hollows and depressions. And in regions where the 

 rock-bottom was composed of the same strata throughout, the 

 superficial accumulations taking place at the surface would 

 naturally assume a great sameness of character. 



But we cannot so account for the presence of the wide and 

 deep masses of loss which characterise such valleys as those of 

 the Rhine and the Danube. The considerable elevation attained 

 by the deposits in question, and their vast extent, have led 

 many geologists to believe that they could not have been laid 

 down by flooded rivers, and an outline has been given (Chapter 



