PROCEEDINGS OF THE COTTESWOLD CLUB 5I 



Four of the above-named strata, viz. : 



The Lower and Upper Lias Clays 

 ,, Fuller's Earth 

 „ Oxford Clay 

 „ Kimmeridge Clay 

 are impervious, and as a rule are valueless as spring water 

 producers, the rain water falling on their surfaces flows 

 over, rather than from, these clay beds. 



Ahhough few or no springs rise or have issue from 

 these retentive clays, they are, however, of significant 

 importance to the supply of water in the Thames basin. 



The drainage area of the Thames comprises two distinct 

 basins, an upper and lower, outwardly connected by a well- 

 defined area or space of about 4 miles between the eastern 

 and western escarpments of the Chihern range ; this plain 

 or space is occupied by the Thames from Moulsford and 

 South Stoke, to Streatley, Goring, Basildon, Pangbourne 

 and Reading. 



The strike of the south-western and north-eastern 

 Chalk and Greensand escarpment ranges from Swindon 

 and Wallingford to Wendover and Tring.* The strike of 

 the lower tertiary beds ranges from Hungerford to 

 Newbury, Reading, Windsor, Rickmansworth, and Watford 

 to Hertford.t 



The space between these two almost parallel lines is 

 occupied by the chalk, averaging 16 miles in width, and 

 determines the upper part of the lower basin of the 

 Thames above noticed, or between Dorchester and Reading. 

 To the north of the strike of the Lower Cretaceous series, 

 the rocks of the Cotteswolds occupy an area of nearly 

 1,640 square miles. 



* Within tlie Thames W.itershed. 



tThis line is nearly parallel to that of the Cotteswold Jurassic or Upper Tluimes 

 Basin, the drainage and slope of which is towards and under the great spread of tlie 

 chalk to Reading, Hungerford, and Windsor, &c. 



D2 



