88 PROCEEDINGS OF THE COTTESWOLD CLUB 



the Ock and Thame all throw great volumes of water 

 into the Thames above Wallingford, for which the geolo- 

 gical structure of this extended area at once accounts. 

 We must not, however, forget to notice that in many 

 localities these clays are covered with drift gravel and 

 sand, the depth of which is often so considerable that 

 percolation through them to the underlying Oxford, 

 Kimmeridge, and Gault Clays, results in the issue of large 

 springs, which become perennial. These complications 

 make it almost impossible to always identify the respective 

 sources of flood and perennial waters, or even to limit 

 them to certain strata. 



From eight miles west of Cricklade to Oxford the 

 Thames runs over the Oxford Clay, and is the mere 

 carrier of waters derived from its tributaries ; those which 

 run from north to south and from north-west to south- 

 east, as the Churn, Coin, Leach, Windrush, and Evenlode, 

 cut their way across the strike of the Lias, the Oolites 

 proper, and the Oxford Clay to the Thames. The 

 Cherwell has a direct north and south course also directly 

 flowing across the strike of the Lias, and Lower and Middle 

 Oolites to Oxford, and is the source, or cause of extensive 

 floods. 



Those streams which flow from south to north have their 

 sources in the Chalk Hills, from the escarpment of which, 

 they receive the back drainage, slightly augmented by that 

 of the Upper Greensand, and then pass over the Gault 

 and Kimmeridge Clays either by the Ray or Cole, or as 

 affluents of the Ock and Thame, which are the main 

 sources of the water carried by these tributaries into the 

 Thames from the south and east, or the Swindon and 

 Thame Basins. 



The Thames as before stated is the great carrier of 

 water, whether perennial or flood, brought into it by its 

 tributaries, but we know nothing of the aggregate of the 

 water it carries. There are no available existing data on this 



