52 PROCEEDINGS OF THE COTTESWOLD CLUB 



The lower basin of the Thames is entirely occupied by 

 the Lower Tertiary series, viz. : 

 The Thanet Sands 

 „ Woolwich and Reading Beds, and 

 „ London Clay. 

 All occur in their true succession, resting upon the 

 chalk, and extending from Windsor, under the Metropohs, 

 to near Southend and the German Ocean, a distance of 

 nearly 70 miles. 



This constituting the London Basin, or within the 

 Watershed. 



The nine divisions of the Jurassic Rocks constitute the 

 source of a large water system, and four of the Rivers 

 which drain them on the north side of the Thames 

 are above St John's Weir, and have their confluence at 

 Cricklade and Lechlade, viz. : 



The Upper Thames or Swill Brook 

 ,, Churn 



Coin 

 ,, Ampneys (2) 

 The great volume of water derived from these rivers 

 passes over St John's Weir at Lechlade, and is augmented 

 by those streams which rise within the Swindon Basin, 

 viz. : 



The Ray 

 ,, Dance 



,, Highworth Streams 

 ,, Cole 

 Their united volume has been ascertained by gauging 

 the River at St John's Weir below Lechlade. 



Few Catchment Basins are richer in springs than the 

 Thames, and those rising in and from the Oolitic rocks 

 above Oxford and Abingdon, and the extensively devel- 

 oped cretaceous series south of Abingdon to Wallingford 

 and Mongewell, constitute a large proportion of the pure 

 water supplied to the middle basin of the Thames. 



