*S'. S. Buchnan — River Development. 



371 



they diverge towards the main stream instead of converging. There 

 are two explanations of such divergence, one where streams rise 

 from a central domelike elevation and flow off in a radial manner; 

 such, I presume, is the drainage of Dartmoor. But there is no 

 evidence for any domelike elevation in the north-west Cotteswolds, 

 and moreover the other rivers of the district do not accord therewith. 

 That explanation cannot be right here. The other explanation may 

 he tried, it is more elaborate. It is that these tributaries of the 

 Severn-Avon have worked back in and now occupy valleys which 

 were originally marked out by streams that flowed in the opposite 

 direction, namely, with the dip, before the Severn valley had been 

 made, and these streams converged to join the Thames river-system. 

 This theory, says Mr. Strahan, transgresses the limits of legitimate 

 speculation. At any rate, however, it has the merit of agreeing 

 with facts, such as those of the dip, of the breaches in escarpments, 

 of the river distribution ; and it gives a logical explanation of 

 river phenomena. It supposes an original river-system flowing 

 off the Paleeozoic rocks of Wales on to the Secondary rocks of 

 England, cutting channels in Oolites and Chalk on its way to the 

 sea. An analogous condition of affairs in the case of the river- 

 eystem of the east side of the Pennine range can be pointed to. 



ri5 5. 



Fia i- 



Fig. 3. — Actual directions of tributaries on left bank of Severn-Avon. 



Fig. 4. — A south-dipping Malvernian anticlinal axis — outcrop of beds 1-4 after 



denudation. A, A, line of outcrop of covering bed 5 after a second uplift and 



denudation. 



The main features of the theory, rivers flowing with the dip, the 

 effect of differential denudation, river growth and river capture, had 

 occurred more or less independently to various observers. To 

 Professor Davis belongs the great merit of bringing the ideas as 

 it were to a focus, giving them practical application, working out 

 a definite theory, and especially pointing out the evidence for river 

 capture. Following his lead again, I may now give the theory 

 application to the district under discussion, and a little elaboration 



