of bedding may be seen, and the beds have yielded fresh-water shells. This, however, is exceptional. Löss is, for the most part, a subaerial accumulation—a wind-blown deposit. This is shown not only by the rounded character of its minute constituents and by the general absence of bedded arrangement, but by the abundant presence of snail shells and the frequent occurrence of relics of land animals. Its organic remains are essentially terrestrial. Moreover, its particular distribution—the mode in which it occurs — points clearly to the action of prevalent winds. Thus, although it is widely developed over low-lying regions, it nevertheless sweeps up to heights of 200 to 300 feet and more above the bottom of the great river valleys. Not only so, but ever and anon it extends across the hills and plateaus between adjacent valleys, wrapping the whole land, in short, like a mantle. Again, in many places, we find it heaped up in the lee of hills, the exposed windward slopes of which bear no trace of it, while in certain valleys it shows a similar partial distribution.
Among the organic remains yielded by the löss are some that indicate arctic conditions, while others are strongly suggestive of a steppe climate, and yet others tell us of forest lands. It is impossible that all the creatures referred to could have lived side by side in the same region, and annual migrations will not wholly explain their appearance in the same deposit. The evidence leads to the conclusion that the accumulation of the löss must represent a long period of time daring which climatic changes took place. Fortunately now and again the lössic accumulations exhibit a succession of faunal zones—different suites of organic remains occurring at different levels. And a similar and corresponding succession has been discovered in many of the caves of middle Europe.
A tundra fauna is the earliest of which we have any record in the löss and in the particular caves referred to, and it is worth while to glance for a moment at the former wide distribution of that fauna in Europe. It will be remembered that two of the most characteristic tundra forms are the banded and the Obi lemmings. Now, remains of both these species have been met with again and again over all central Europe—in Russia, Poland, Austria-Hungary, north and south Ger- many, north Switzerland, France, Belgium, and England. Sometimes they occur in single specimens, at other times they are extremely numerous, the remains of several hundreds having been obtained at various localities. In many places both species of lemming are found together; elsewhere either one or other occurs alone. The banded lemming, as a rule, has left its remains most abundantly in hilly and upland tracts, while those of the Obi lemming are met with more frequently in low-lying areas—a distribution quite in keeping with that which obtains at present in the tundras. That these arctic animals were not mere passing or occasional visitors is shown by the fact that young and full-grown individuals occur together in hundreds at various
