GEAVELS SOUTH OP THE THAMES EROM GUILDEORD TO NEWBURY. 29 



3. On the Gravels south of the Thames from Guildford to 

 Newbury. By Horace W. Monckton, Esq., P.G.S. (Head 

 December 23, 1891.) 



The greater part of the hill-gravel in the district to which the 

 following communication refers belongs to the Southern Drift of 

 Prof. Prestwich,! and a very large portion of the valley-gravels 

 consist of materials mainly derived from the Southern Drift. It is 

 only on the hills between Cookham and Twyford, and at Tilehurst 

 near heading, that we get the Westleton Shingle of that author or 

 the Glacial Gravel. 



The distinctive features of the Southern Drift are given at length 

 by Prof. Prestwich.^ Briefly it may be said to consist of materials 

 derived from the Wealden area of Kent, and Surrey, the Chalk 

 country to the north and west of the Weald, Eocene formations of 

 the neighbourhood and older gravels, or possibly older clay with 

 flints and surface-debris. It is, I believe, the gravel of old rivers 

 which had little or no relation to our present river-system, whilst 

 the gravels of the valleys, terraces, and minor plateaux are the 

 work of rivers having some, though often a distant, relation to those 

 now in existence. 



The Southern Drift of the district under consideration may con- 

 veniently be divided into three classes. The first includes certain 

 patches on very high ground along the margin of the Wealden area, 

 obviously the oldest gravels in the district. The second consists of 

 material largely derived from the Lower Greensand of the Wealden 

 area and extends as far west as Strathfieldsaye ; while in the third, 

 which lies west of that place, there is an absence of such material. 

 It wHL be observed that in dealing with these gravels the writer 

 rejects all theories which suppose them to have been formed by 

 marine agency. I do not believe that the sea has flowed over this 

 part of England since the oldest of these gravels was formed — pro- 

 bably not since the earth-movements took place which separated 

 the London and Hampshire Eocene basins. The facts which will 

 now be detailed are not, however, affected by this opinion, and are 

 of equal interest whether it be right or wrong. 



The gravels with which I am dealing possess an extensive lite- 

 rature. It hardly appears necessary, however, to give an abstract 

 of the various papers and books dealing with them, though niany 

 of them will be referred to in the following pages. But I should 

 like at the outset to acknowledge my indebtedness to the paper by 

 Prof. Pupert Jones,^ to that by Dr. Irving,* and to Mr. Whitaker's 



1 Quart. Journ. Geol. Soc. vol. xlvi. (1890) pp. 84, 120, 155. 



2 aid. pp. 155, 156. 



3 ' On the Physical Features of the Bagshot District,' Proc. Geol. Assoc, 

 vol. vi. (1880) p. 429. 



^ * On the Bagshot Strata of the London Basin and their Associated Gravels,' 

 Proc. Geol. Assoc, vol. viii. (1883) p. 143. ' ^ 



