THE TUNDRAS AND STEPPES OF PREHISTORIC EUROPE. 337 



While all northern and northwestern Europe were covered by an ice 

 sheet, the mountains of middle Europe and the alpine lauds supported 

 great glaciers, which in many cases deployed upon the low grounds. 

 Vast bodies of water must then have escaped from the terminal front 

 of the northern mer de glace, while the streams and rivers flowing from 

 our mountain tracts must have greatly exceeded their present succes- 

 sors. With each recurring spring and summer wide areas in the low 

 grounds would thus be subject to floods and inundations. Coining 

 from regions where glacial grinding was being carried on upon a most 

 extensive scale, it goes without saying that all these waters would be 

 clouded with the fine flour of rocks. The enormous morainic accumu- 

 lations formed underneath and in front of the alpine glaciers, and over 

 the vast areas traversed by the Scandinavian mer de glace, bear em- 

 phatic testimony to the intensity of glacial erosion. In like mauner 

 the great terraces of gravel that stretch down the valleys in front of 

 the alpine moraines and the broad sheets of similar deposits which 

 extend outward from the glaciated tracts of northern Europe, are 

 equally impressive witnesses to the vigor of the flooded glacial rivers. 

 It is certain, however, that gravel, grit, and sand would not be the 

 only materials carried forward by those rivers. As they reached the 

 low-lying tracts their rate of flow would gradually diminish, and finer- 

 grained materials — fine silt and loam — would eventually be deposited. 

 When we consider the great volumes of water descending to the low 

 grounds, we can not, indeed, escape from the conclusion that many 

 wide areas in the plains during a glacial epoch must have been inun- 

 dated, and in those slack waters and temporary lakes the finer-grained 

 fluvio-glacial sediments would tend to accumulate. We must also bear 

 in view the probability — I had almost said the certainty — of great 

 derangements of the drainage having taken place in middle Europe. 

 In winter, when the rivers of that region were frost bound, snow must 

 frequently have drifted to great depths in the valleys, and the spring 

 and summer thaws would often fail to remove these heaps. In this 

 way the valleys might here and there become entirely filled with the 

 blown and congealed snows of successive years, so as to compel the 

 rivers in summer to rise in flood and to reach levels which they might 

 otherwise have been unable to attain. We have positive proof, indeed, 

 that such accumulations of drift snow actually did appear in extra- 

 glacial regions, for some of them have persisted to the present day. 

 The ice formations of the arctic coast lands, with their associated mam- 

 malian remains, certainly belong to the glacial period. They are 

 simply the drifted snows, now converted into granular and massive 

 ice, which accumulated in valleys and depressions outside of the gla- 

 ciated regions. Protected under a covering of superficial detritus, 

 alluvial matter, and peat, they have in those high latitudes persisted 

 to the present day. Farther south, in central and western Europe, 

 similar masses of congealed snow, as we have seen, appear to have 

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