In the long ages which elapsed between the close of the pleistocene period and the dawn of history other races than these may have occupied Europe, and have passed away without leaving any clue as to their identity. But in the present state of our knowledge we are justified only in concluding, that the oldest population in prehistoric times was non-Aryan, the traces of which are left behind not merely in the caves and tombs, but in language,[173] and in the small dark-haired inhabitants of western and southern Europe. The prehistoric peoples lived under physical conditions very different from those of central and western Europe at the present time; the surface of the country being covered with rock, forest, and morass, which afforded shelter to the elk, bison, urus, stag, megaceros, and wild boar, as well as to innumerable wolves. They arrived from the east with cereals and domestic animals, some of which, such as the _Bos longifrons_ and _Sus palustris_, reverted to their original wild state. From the very exigencies of their position they lived partly by hunting, and they gradually pushed their way westward, carrying with them the rudiments of that civilization which we ourselves possess. It is an open question whether they came into contact with the palæolithic races which preceded them. The climate which they enjoyed was sufficiently severe to allow the reindeer to inhabit the district on which now stands the city of London, and its severity may also be inferred from the thickness of the bark of the Scotch firs, observed by Mr. Godwin-Austen in the submarine forests of the south of England, and by Mr. James Geikie in those of Scotland. The area of Great Britain was greater then, than now, since a plain extended seawards from the coast-line, nearly everywhere, supporting a dense forest of Scotch fir, oak, birch, and alder, the relics of which are to be seen in the beds of peat, and the stumps of the trees, near low-water mark on most of our shores. And it may be inferred that the forest extended a considerable distance from the present sea margin, from the large size of the trunks of the trees.[174] CHAPTER VIII. THE PLEISTOCENE CAVES OF GERMANY AND GREAT BRITAIN.