and preserved at that time. Many of the so-called "rubble drifts" of middle Europe—sheets of rocky rubbish which have traveled down gentle hill slopes and spread themselves over the adjacent low grounds—point to the former presence of great snow drifts, in and upon which the rock debris traveled. These were not glaciers, but simply sheets of neve-like snow, charged with and covered by earthy and rocky debris, which kept moving outward, more especially in spring and summer when the heaps were more or less rapidly melting. The occurrence in this debris of bones of the reindeer and other mammals shows that the deposits belong to prehistoric times. Again, certain phenomena connected with the river gravels of the same period lead to the conviction that the drainage was often interfered with by snowdrifts in tundra times. The river valleys would seem to have become filled in places with alternate sheets of congealed snow or ice and layers of gravel and shingle. Long afterwards, when the interbedded strata of ice melted slowly away, the associated river detritus quietly settled down, and owing to the differential movement of the subsiding materials the longer stones naturally arranged themselves in lines of least resistance, so that now we find them most usually standing on end in the gravel beds.
Thus, apart from the evidence supplied by the bone accumulations of the loss, we have good reason to believe that snowdrifts were of common occurrence in middle Europe in prehistoric times. Doubtless most of the snow which covered the plains of our continent in winter melted and disappeared in summer, just as is the case in the tundras and steppes of our own day. The carcasses of animals that may have perished in blizzards would thus most frequently become uncovered in spring, to be devoured by hyenas, wolves, and bears, and the disarticulated skeletons might often be bleached and weatherworn before they were finally buried in loss. Nor was it only in plains and open valleys that sudden death may have overtaken large numbers of animals at a time. In tundras and steppes alike the wild and semiwild denizens of the plains seek refuge from the drifting snow in the fissures, caves, gullies, and ravines of the hills and mountains, where they are sometimes frozen to death or smothered in snow. Herbivorous and carnivorous animals thus often perish together, for in the presence of a common danger, whether it be prairie or forest fire, or flood or blizzard—natural antipathies and animosities are forgotten, and all alike struggle to escape.
Man, as I have already mentioned, lived in middle Europe in tundra times, and we have abundant evidence of his presence there throughout the succeeding steppe epoch. Again and again his relics and remains have been met with at all levels in the loss throughout central Europe. Thus in the valleys of the Danube and some of its tributaries they have been discovered in undisturbed löss at depths of from 20 to nearly 100 feet from the surface. Not a few of these finds evidently represent old prehistoric camping stations—marked by the presence of quantities of
