1900 S. S. BUCKMAN — EXCURSION NOTES 185 



hank of the Cohi just below the allotments north of 

 Withington, and even better in the valley from Syreford 

 to Sevenhampton ; secondly, the development of a sub- 

 sidiary concavity in a primary spur : this is well shown in 

 the right bank of the Coin just below the allotments, and 

 on the left bank just below Woodbridge, towards Casey 

 Compton. 



Diminution of river curves indicates diminution in river 

 volume ; the latter would be brought about by the success- 

 ful growth of the Severn, as it beheaded, first the western, 

 and then by means of the Avon, the northern tributaries 

 of the Coin — those which would have cut the pass at 

 Charlton Abbotts. So the fact of finding these diminish- 

 ing curves so plainly in the Coin valley is strong evidence 

 for the assumption that the original Thames streams 

 flowed from the Welsh hills over the Cotteswolds before 

 any Severn existed, as in Fig. 12; and that the present 

 condition of the drainage is due to their having been 

 successively broken into by the Severn working along the 

 strike of the soft Lias rocks. 



A glance at Fig. 12 will show the possibihty of the 

 Bristol Avon doing the same for the streams which enter 

 the Goring gorge, as the Severn is supposed to have 

 done for those entering the Chelt gorge, and so leaving 

 the Goring gorge as a riverless breach such as the Chelt 

 gorge is now. The Bristol Avon would have to work 

 back along the line of the Thames to Oxford ; and it may 

 be seen that it has already accomplished the process in 

 part, and has captured some of the South Cotteswold 

 streams which, by analogy with their neighbours, the 

 Churn and Coin, there is every reason to suppose once 

 formed part of the Kennet {i.e. Thames system) drainage. 



