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686 At Caddington the discoveries are quite consistent with the hypothesis, but point to a period when the excavations of the existent valleys had made but little progress.

Higher up the Thames valley at Reading and at Oxford the phenomena are all in accordance with the hypothesis; at the former place the river has deepened its valley to the extent of at least 100 feet.

The discoveries in the gravels capping the North Downs and those made near Ightham and Limpsfield in the transverse valley at the foot of the Downs, seem at first sight difficult to reconcile with any river-theory. But assuming that the beds capping the hills were at one time continuous with others in the Wealden area, and that the transverse valley was produced by denudation at a later date, the difficulties disappear, though the time requisite to effect such superficial changes may seem to be immense.

Passing by other localities where implements have been found in the valley of the Thames, such as Swanscombe and Northfleet, though it may be observed that the gravels in which they have occurred are, on the river-theory, exactly where they might have been expected to be present, we come to the beds near Reculver, where they have been found in large numbers. Looking, however, at the enormous encroachment of the sea, even within the last few centuries, upon the soft cliffs of sand and clay at that spot, it is difficult to form any satisfactory idea of the conditions under which a river may have flowed near the spot at a remote period, or of the position of the coast at the time. Where, however, as is here the case, a large tract of land has been washed away, which must of necessity have had its system of superficial drainage by streams, and may possibly have had rivers passing through it, which now, owing to the altered conditions, find their way into the sea at a point much nearer their source than formerly, we should expect to find on the top of the cliffs traces of the former state of things; and where any portion of the slope of an old valley remained, to see its gravels, though now so close to the sea, at a height far above its level. Still, it is hard to say whether the implement-bearing beds at Reculver are connected with the old valley of the Thames, or with that of some other stream which has now disappeared, but of which the upper portion is to be traced in the Swale, which now separates the Isle of Sheppey from Kent, and which appears to afford, in its junction with the West Swale and Long Reach, an instance of two valleys being gradually eroded inland until they met. The beds may even be connected with the