23 i J03EPH PRESTWICH, T.R.S., F.G.S., ON A TOSSIBLE 



of the same inuudatiou which produced the deposits of loam 

 and gTavel in whi(;h they are imbedded."* 



This view, which was held by many distinguished men, was 

 however soon found to be untenable. An universal deluge 

 was recognised to be a physical impossibility, while further 

 research led to the conclusion that the superficial loams, gravel, 

 and sand, instead of being tlie result of one rapid rush of 

 waters over the surface, were due to the prolonged action of 

 the several local agencies still acting on the surface of the 

 globe. Such as (1) large spreads of gravel and sand are now 

 known to have been deposited on the flanks and terraces of 

 our valleys by the old Rivers, when, before they had exca- 

 vated their channels to the present depths, they flowed at 

 various higher levels. That this was their origin is shown 

 by the fact that these deposits contain fluviatile shells, 

 mostly such as now live in our rivers, together with the rolled 

 and worn bones of the contemporary land animals. The pre- 

 servation of such remains is, however, partial and irregular, 

 because the beds in which they are entombed are in general 

 so permeable that the percolation of the surface waters has 

 very commonly removed the calcareous matter of the bed 

 itself together with tliat of the embedded shells and bones, but, 

 where these have been protected by beds of loam or clay, 

 the organic remains are often well preserved. The higher 

 and older the terrace, the more rare are the organic remains. 

 (2) Another large series of these deposits contains rock 

 debris and boulders, transported far from their native place. 

 This was formerly looked upon as evidence of the rush of 

 the diluvial waters, but now it is well established that these 

 boulders have been carried to their present positions by the 

 slow action of either land or floating Ice and not by any 

 sudden transport by water. (8) Other portions of the Drift 

 are of marine origin, as indicated by the presence of sea- 

 shells, while subaerial processes, weathering, etc., have in 

 places contributed to the general result. 



In this way the origin of the larger proportion of the super- 

 ficial deposits of loam, gravel, and sand has been accounted 

 for, and shown to be due to the same agencies, though often 

 acting with greater intensity and force than those which 

 now act upon the surface of the land ; and that so far from 



* Bucklaud, Reliquue Dilui-iana', pp. 184, 185. 



