PROCEEDINGS OF THE COTTESWOLD CLUB 79 



the south-east, has an important bearing upon the water 

 system of the Cotteswolds, and equally so upon the 

 construction of reservoirs on any of the several rivers 

 above Oxford. Again, to better understand the flow of 

 water in the Churn, the Ampneys, Coin, Windrush, and 

 Evenlode, it is important to notice where the Lias 

 disappears both along the beds as well as sides of the 

 Rivers. 



A line drawn from Rendcomb on the Churn to between 

 Compton, and Yanworth on the Coin, Hampnet, north 

 of Northleach, and Farmington, thence by Sherborne and 

 Little Harrington to Burford, nearly determines where 

 the Impervious Lias ceases to occupy the beds of the 

 rivers named ; throwing out the confined waters in the 

 form of springs, this water being derived from the over- 

 lying porous and jointed beds of the Inferior Oolite 

 south-east of this line. The surface area is occupied 

 by the Impervious Fuller's Earth, Great Oolite, and 

 Forest Marble. 



The absorbed rainfall over the two latter rocks is held 

 up below ihem by the Fuller's Earth, which releases 

 through the agency of numerous east and west Faults 

 the accumulated drainage from its watertight under- 

 ground surface. 



The limit of the area occupied by the Fuller's Earth 

 between the loss of the Lias at Rendcomb on the Churn, 

 Compton on the Coin, Farmington, Sherborne and 

 Burford on the western side of the Windrush is clearly 

 defined by this line, below \vhich all water accumulated 

 upon the Lias is lost to the Thames. 



The springs of Yanworth, Slowell, Foss Bridge, Coin 

 St Dennis, Coin Regis, Winson, Arfington, and Bibury, 

 are entirely governed and thrown out by the underlying 

 Fuller's Earth Clays, which occupy the bed of the Coin 

 from the Stowell fault, to the fault and great spring at 

 Bibury, south of which all traces of the Fuller's Earth 



