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 A HISTORY OF SURREY district, although it is true that now and again we have found the forces of destruction and reconstruction going hand in hand even within this limited field of observation. But henceforward we shall have to deal only with the shaping of the land as the strata which we have been con- sidering were uplifted above the waters and broken down piecemeal by rain, frost, heat and wind, to be carried away by brooks into rivers and by rivers into seas, to take their part in the construction of a newer land. In the passage, seaward, however, the detritus of the land makes many halts. It forms gravel-banks and flats in the streams, of which portions are sometimes left stranded for a while as terraces on the slopes when the valley is deepened ; it is blown by the wind from dry channels and spread over tracts where it may find temporary rest ; or it is carried as mud by river-floods and deposited on low ground beyond reach of im- mediate re-transport. In these and other similar ways, the remnants from the waste of the land, termed by geologists the ' superficial ' deposits, are formed ; and as we shall presently see, we may glean from their examina- tion some knowledge of conditions which though geologically ' recent ' are still long since past. It is not indeed certain that because no newer ' solid ' strata than the Bagshot Beds now exist in our county none were ever deposited ; in Hampshire there are newer (Oligocene) beds several hundred feet in thickness ; but if such were ever laid down in Surrey they have since been entirely removed. Of a still later period the Pliocene it is be- lieved that there are actually some faint traces in the form of small masses of ferruginous sand and loam which are preserved in ' pipes ' or hollows of the chalk in a few places on the summit of the Downs. No conclusive evidence has yet been found in Surrey to indicate the age of this material, though it has recently yielded a few ill-preserved traces of shells at Netley Heath, while in hardened sand similarly situated at Lenham and Harrietsham in Kent the casts of marine shells of Early Pliocene age have been discovered. 1 DEEP-SEATED ROCKS Before following the later development of the geological history of our county, however, let us turn back for a moment to investigate its very foundations. We started our examination with the oldest rocks which are exposed at the surface ; but as previously mentioned there have been two deep borings in the north of the county which have proved the existence of a sequence of much older rocks at considerable depths below the surface. These borings were made at Richmond and at Streatham, and their results are arranged and classified in the following summary. In both records the lower portions printed in italics represent strata older than those exposed at the surface in Surrey, or indeed in any part of the south-east of England. 1 See C. Reid, Mem. Geol. Survey, ' Pliocene Deposits of Great Britain ' (1890) p. 48 ; and W. P. D. Stebbing < Excursion to Netley Heath and Newlands Corner,' Proc. Geol. Assoc., vol. xvi. (1900) pp. 524-526. 18