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Rh Palæolithic implements occur on the surface of the ground and in beds of gravel. The latter, which may be conveniently considered first, may be divided into the following three classes: (1) deposits of gravel in the form of terraces near the beds of existing rivers, such as those in the valleys of the Thames, the Stour, and the Cray; (2) deposits occupying valleys which, although obviously shaped to a large extent by river action, are now dry; and (3) deposits on elevated ground, such as those on the North Downs.

The occurrence of palæolithic implements in the gravels of the Thames Valley at Swanscombe, Northfleet and other places in Kent as well as in Middlesex, Essex, etc., is of great interest because on examination it will be found that many of the implements have been worn in just the same way as have the flints of which the gravel is composed. They have clearly been subjected to the same abrading forces, and therefore they must have been shaped by man at a period prior to the deposition of the gravel. It is also equally clear that the waters of the river have much diminished since that time.

The second class of deposits, occurring in valleys which are now dry, are admirably illustrated by the implement-bearing gravels of West Wickham, the upper part of the Valley of the Cray, etc. As these implements are to a very large extent much drift worn, it is pretty clear that they must be referred to an origin quite as remote as, if not more remote than, the period when these dry valleys were important water-courses.

The third class, to which the high level gravels on the top of the North Downs belong, presents a more difficult and complicated problem. If these deposits of drift-worn gravel have ever been connected with a river system it is certain that very great changes must have been produced subsequently by denudation, and it seems at any rate probable that they were intimately associated with the forces by which the Wealden district was denuded.

Considerable interest has been aroused in recent years by discoveries of paleolithic implements in an abraded condition and lying at great altitudes on the chalk, plateau. The subject has already been discussed by the late Professor Prestwich and others. Some antiquaries as well as geologists (for the question comes within the scope of both archæology and geology) have been inclined to think that an interval of time, far greater than had hitherto been imagined, has elapsed since the implements were made; but the conclusion seems rather rash and entirely without scientific value, seeing that we have no positive, nor even approximate data as to the rate at which the changes of level, whether produced by denudation or otherwise, have been effected.

In order to distinguish these high-level implements from others occurring at lower levels the term eolith was applied to them, and 309