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Rh sculptured prior to the Glacial epoch, yet during that epoch and in subsequent times considerable modifications were brought about by the accumulation of material as well as by erosion.

The valley gravels which border the present rivers lie in hollows cut through the plateau Drifts. They are evidently newer, but whether they are wholly Post Glacial is difficult to decide, as in both North and South Wales there is evidence that Glacial action continued later than some of the deposits which contain mammalia, like those found in the older Thames valley deposits.

If following Ramsay we believe that the Thames drainage com- menced when the Chalk and Eocene strata extended much further to the west and north-west, and flowed across a gently inclined plane towards the south-east, its general course was marked out perhaps in Miocene times ; but there are no deposits along its valley which date back beyond the Pleistocene period. Subsequent physical changes may have removed such deposits, while the wasting away of the Chalk escarpment must have modified the extent and direction of the drain- age. The Bedfordshire Ouse, according to Professor W. M. Davis, was a subsequent stream which beheaded certain northern streams originally connected with the Thames drainage. Among these is the Tove, which now joins the Ouse near Stony Stratford ; while the Ouzel may have been formed later on as an obsequent stream, as it flows northwards into the Ouse at Newport Pagnell. The Thame is regarded as a subsequent stream, and likewise the Colne which cuts off the waters of the Misbourn and Chess.

If however we judge by the mammalian and other remains found in the gravels of these valleys, it is difficult to make any distinction in point of age. They all belong to the Pleistocene period. Thus in the Thame valley, not far from the borders of Buckinghamshire, between Shabbington and Rycote, remains of elephant have been found.

At Taplow remains of the musk ox have been discovered, and in the lower parts of the Thames valley the gravels and brickearths have yielded many mammalian remains and palaeolithic implements. Again in the Ouse valley of Bedfordshire there have been found numerous palaeolithic implements ; and in the Ouzel tributary remains of elephant (mammoth) have been recorded from Linslade.

The Alluvium, which is the tract of level ground bordering the streams and liable to be flooded when they overflow their banks, occupies but small areas in the county. Wider tracts are seen along the Colne valley than along the Thames or the Ouse. These are mostly meadow land, and should always be avoided as sites for human habitations. Even the low-lying valley gravels bordering the Thames are liable in places to be inundated, and elsewhere they may prove damp as sites for dwellings, hence all living rooms should be well