valley was scooped out. It is a portion of the great marine glacial drift of the midland counties of England, and contains blocks, some of large size, not only of the oolite of the neighbourhood, but of chalk and other rocks transported from still greater distances, such as syenite, basalt, quartz, and new red sandstone. These erratic blocks of foreign origin are often polished and striated, having undergone what is called glaciation, of which more will be said by and by. Blocks of the same mineral character, embedded at Biddenham in the gravel No. 3, have lost all signs of this striation by the friction to which they were subjected in the old river-bed.
The great width of the valley of the Ouse, which is some times two miles, has not been expressed in the diagram. It may have been shaped out by the joint action of the river and the tides when this part of England was emerging from the waters of the glacial sea, the boulder clay being first cut through, and then an equal thickness of underlying oolite. After this denudation, which may have accompanied the emergence of the land, the country was inhabited by the primitive people who fashioned the flint tools. The old river, aided perhaps by the continued upheaval of the whole country, or by oscillations in its level, went on widening and deepening the valley, often shifting its channel, until at length a broad area was covered by a succession of the earliest and latest deposits, which may have corresponded in age to the higher and lower gravels of the valley of the Somme, already described, p. 130. Mr. Prestwich has hinted that perhaps the drift of Biddenham, which is thirty feet above the present level of the Ouse, and contains bones of Elephas primigenius, and the shells above alluded to, may be a higher level alluvium; and the gravel on which, the town of Bedford is built, which is at an inferior level relatively to the Ouse, may be a lower deposit and consequently newer. But we have scarcely as yet sufficient data
