Near Buckingham, at Tingewick, Radcliff and elsewhere coarse boulder gravel with large blocks of Oolitic rocks and finer gravel and sand occur with intercalations of Boulder Clay.
If we believe that the main mass of Boulder Clay was formed on the land, that much of it was overridden and pressed down into the tough material which it usually is, and that it was left on the melting back of the ice sheet, we might expect, along the borders of the glaciated area, to find alternations of gravel, sand and Boulder Clay. The ice during fluctuations in climatic conditions extended and receded for some distance more than once before it finally retreated, and the melting of the basal portions gave rise to such diverse sedimentary accumula- tions, largely torrential, as in fact we find near Buckingham.[1]
It may be therefore that over the Chalk tracts which were not glaciated the brickearths and gravels of the plateaus belong to the marginal area of the ice sheet, whence more or less mixed deposits were spread out by the flood waters.
VALLEY GRAVEL AND BRICKEARTH
In the higher courses of the Chalk valleys, where no streams now flow at the surface, or only occasionally in times of excessive rain, we find accumulations which have been termed ' Dry Valley Gravel ' largely made up of loam with unworn and broken flints, a waste from the clay-with-flints and brickearth and occasional gravel beds of the bordering hills. These merge in the lower courses into the ordinary valley gravel, as between Wendover and Great Missenden.
The gravels of the Thames valley extend over broad tracts near Great Marlow, Burnham, Dorney, Eton, Wraysbury and Colnbrook, thence merging into the gravels of the Colne valley by Denham. They consist of angular, subangular and rounded flints, with pebbles of quartz and quartzite, and are exposed in pits to a depth of 1 2 or 15 feet or more. Over considerable areas there are sheets of brickearth which at Slough and Langley have been worked for brickmaking.
We have thus in these lower lands the same kinds of deposit as occur on the Chalk and Tertiary plateaus, but the valley deposits yield the mammalia characteristic of the Pleistocene deposits, and palaeolithic implements. They are distinctly river deposits, although in composition the gravels naturally do not differ from the higher beds from which they were mainly derived ; and near Great Marlow it is difficult in places to separate the higher terraces of river gravel from the plateau Drifts.[2]
In the Ouse valley we find gravels at Buckingham, Stony Stratford, Stanton, Lathbury, Tyrington and Filgrave, Emberton, Olney and Cold Brayfield ; and in the Ouzel valley there is gravel at Linslade, Fenny Stratford, Woughton-on-the-Green and Newport Pagnell. Along the borders of this valley there are extensive tracts of grazing land. Although the main features of the country appear to have been
22
