caves and rock-shelters, to which so many of the inhabitants resorted on the recrudescence of the last great glacial epoch, were in sufficient numbers to afford accommodation for all persons who suffered from the increasing severity of the climate. What protective means did these open-air nomads adopt? We have no evidence to show that they dug holes in the earth and covered them with wooden roofs, as the Neolithic folk did in the construction of their well-known hut villages.
Similar difficulties beset archaeological researches in the English drift deposits containing Palæolithic implements. At various levels on the flanks of the present valley of the Thames are found a series of gravel terraces, deposited by the river at various stages in its history, precisely analogous to the gravel terraces of the Somme Valley. The lowest of the Thames terraces is 10 to 25 feet above the present level of the river, the others being respectively 60, 100, and 200 feet high. But the modern river does not lie at the bottom of the maximum depth of the basin, as at Tilbury it is upwards of 70 feet lower. When the Tilbury docks were being excavated, it was proved that the bank of the river was composed of sedimentary gravel, peat, and the debris of the successive land-surfaces containing human remains. This shows that the valley has been gradually sinking for a very long time, probably for many thousands of years. Also at various heights above the present river, Palæolithic floors have been described by several competent investigators. Such habitable sites with remains of workshops for the manufacture of flint tools have been recorded by Mr Worthington G. Smith, at Caddington, and by Mr F. C. G. Spurrell, as existing at Crayford, a station on the south bank of the Thames, and described in Chapter IV.
Moustérien.
Among the earliest caves inhabited by man was that of Le Moustier, situated on the right bank of the Vézère, and about 90 feet above it. It was examined by Messrs Lartet and Christy in 1863, and subsequently by de Vibraye, Massénat, and others. Besides the deposits in the interior of the cave, there was an outside plateau in which human skeletons have been recently found, and which will be described later on.
