96 PROCEEDINGS OF THE COTTESWOLD CLUB 



Between Abingdon and Reading the course of the 

 Thames is entirely over the Lower Greensand, Gault, 

 Upper Greensand and Chalk* falling from 179 feet at 

 Abingdon to 67 at Eton, or 112 feet. 



Between Culham and Dorchester the Thames flows 

 between the sharply defined beds of the Lower Greensand 

 and Gault, the former on the north side as far as Burcot, 

 thence to Day's Lock and the mouth of the Thame over 

 the Gault — from the Thame to Bensington Weir between 

 the Gault and Upper Greensand and from the Great 

 Bensington Weir to Mongewell, three miles over the 

 Upper Greensand ; thence for four miles to the Gap in 

 the Chiltern Hills between Streatley and Goring and on 

 to Pangbourn. 



Reservoirs 



The question of obtaining suitable sites or localities 

 for the construction of reservoirs, either for the recep- 

 tion of pure spring, or pure spring-flood waters of the 

 Upper Thames district, is now a question of great im- 

 portance to the supply of water to the metropolis. 



None of the tributary valleys of the Cotteswolds above 

 Lechlade, owing to the porous nature of the Oolitic Rocks, 

 can be utilized ; few, if any, possess either the proper 

 configuration of the ground or condition of rock-structure 

 enabling embankments of sufficient size to be constructed, 

 and watertight reservoirs ensured. 



The Churn, the Coin, and the Windrush, which are 

 typical examples of the Cotteswold Rivers, and the country 

 they drain, would seem at first sight to have all the 

 elements necessary for the construction of watertight 

 reservoirs through embankments thrown across their 

 valleys. The difficulty however arises from the physical 

 nature of the rocks on which such reservoirs would be 



* The Lower Greensand two miles, Gault four, Upper Greensand five. 



