PROCEEDINGS OF THE COTTESWOLD CLUB 53 



The total length of the chief tributaries to the Thames 

 is about 700 miles, the secondary feeders being consider- 

 ably more; there are therefore about 1800 miles of water- 

 way within the area of the Thames watershed, or about 

 one mile of water-channel in every 3^^ square miles. 



The Great Oolite comprises the most important group 

 of permeable strata, representing or occupying a catch- 

 ment area of about 250 square miles, and giving rise 

 to a number of fine and constant springs, among which 

 are those of Boxwell and Baunton on the Churn above 

 Cirencester, the Thames Head, and the Ewen Springs, 

 west of Cricklade, and Siddington, the numerous and 

 copious springs constituting the Boxwell group rising 

 from the east and west fault between the Cornbrash and 

 Oxford Clay, and the variable but fine springs of the two 

 Ampneys. 



The great and constant spring at Bibury, those of 

 Foss Bridge, Winson, Coin St Dennis, Coin Rogers, 

 Ablington, Coin St Andrews, and Quenington, are all on 

 the Coin. These prolific springs are all thrown out by the 

 impermeable clays of the Fuller's Earth, which underlie 

 the Great Oolite and Forest Marble, and they furnish a 

 large proportion of the spring water flowing into the 

 Thames above Lechlade, and the Windrush below. 



The Inferior Oolite extends over an area of about 106 

 square miles. The head of underground waters drained 

 from these porous rocks is great and constant, furnishing 

 several important perennial springs, those of Syreford 

 and Dowdeswell on the Upper Coin, yielding from 

 3,000,000 to 4,000,000 gallons per day. These springs 

 arc thrown out by the underlying impervious clays of the 

 Lias — which extend from the watershed at Charlton 

 Abbots to Withington, entirely draining the extensive 

 spread of the Inferior Oolite. 



In 1867 Mr Taunton gauged the volume of water in the 

 Thames, passing over St John's Weir near Lechlade. 



