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 successors. 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 accumulations formed underneath and in front of the alpine glaciers, and over the vast areas traversed by the Scandinavian mer de glace, bear emphatic testimony to the intensity of glacial erosion. In like manner 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 inundated, 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 mammalian 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 glaciated 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
