GEOLOGY 



the greater part of the country north of the Thames was covered by a 

 vast accumulation of snow and ice, there is much reason to assign the 

 formation of some of the older gravel-deposits of Surrey to this Glacial 

 Period. The ice-sheet during its maximum development spread south- 

 ward as far as the northern margin of the Thames Valley, but there is 

 no evidence of a permanent ice-field to the southward of that valley. 

 Thus the conditions in Surrey at this time would be peculiarly favourable 

 to rapid erosion ; for although the ice-sheet itself planes away the land 

 in its gradual outward flow, it also protects the surface from the severer 

 action of streams and of alternate freezing and thawing. We may 

 picture the Surrey of the Glacial Period as a bleak tract lying just beyond 

 the margin of the ice-fields ; its surface frozen and rendered impervious 

 by the autumn frosts ; then deeply covered by the winter snows ; to be 

 drenched and torn during the thaw in the late spring by the sudden re- 

 lease of the waters. And as the land probably ^tood higher above sea- 

 level than at present, the torrential denudation during the short summer 

 may have been extremely great. The turbid rivers, laden with mud 

 from the disintegrated clays and with stones from the harder strata, 

 deepened their channels rapidly, and cast down wide sheets of detritus 

 wherever their course was checked. Hence, throughout all the Glacial 

 time there was everywhere in the county a rapid wasting of the hills and 

 slopes, and a transference of the material to lower and lower levels. 



In the vicinity of the main valleys, like that of the Thames, it is 

 more or less difficult to distinguish between the lower portion of the 

 high-level accumulations and the higher of the deposits clearly connected 

 with the existing valley, although in some other districts the distinction 

 seems well marked. It is probable that at the close of the Glacial 

 Period there was no such radical change in the conditions in this area as 

 in places which had been actually overridden by the ice-sheet, but only 

 a gradual and progressive amelioration by which the past was merged 

 insensibly into the present. The streams and rivers still maintained their 

 courses and continued to deepen their channels, but with diminishing 

 activity as their flow diminished ; until they reached their present 

 shrunken state, in which the main streams are able to transport only the 

 finer detritus, while many of the smaller head-valleys, especially those 

 traversing the more porous strata, are no longer able to maintain a 

 permanent stream. 



The older of the undoubted valley-deposits are especially interesting 

 from the fact that they yield the earliest indications of ancient man, in the 

 form of coarsely-chipped implements of flint, associated with the remains 

 of extinct animals. 1 Though these ' Palaeolithic ' implements have not 

 been obtained so plentifully in Surrey as in some of the neighbouring 

 counties they have already been recorded from many localities, and fresh 

 discoveries are constantly being made as the search by qualified observers 



1 For numerous records of Palaeolithic and Neolithic implements in Surrey consult Sir 

 J. Evans' Ancient Stone Implements, 2nd ed. (1897), where references to previous literature will 

 also be found. 



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