Vol. 60. ] 



THE VALLEY OF THE TEIGN. 



329 



Of course, the existing depression and dry valley must beloug to 

 the very latest stage of this ancient course of the Yeo, just previous 

 to its capture by a tributary of the Dart. Xo one could indicate 

 precisely the course of the stream which drained the area north 01 

 Ashburton in Miocene and Oligocene times : but my contention is 

 that the drainage of this district (which is now carried into the 

 Dart by the Yeo) was in more ancient times directed along the line 

 of the Kester Brook, and helped to swell the volume of the river 

 which made the Teignmouth Vallev. It is also noteworthv that the 



Fig. 3. — Map of the neighbourhood of Ashburton. 



[Scale: 1 inch = 1 mile. Contours indicated in feet. The double broken 

 lines show the probable ancient course of the Yeo.] 



Yeo rises on Dartmoor at a level of about 1200 feet, and may in 

 ancient times have drained a larger area of the moor than it does 

 at present. So also may the Lemmon. 



TA'e now come to the consideration of the changes which must 

 have greatly modified the system of drainage, and, as I think, led 

 to the diversion of certain rivers from an easterly course to a 

 southerly one. These changes were partly regional, and partly 

 local. 



The regional change was that which greatly augmented 

 the elevation of the AVealden anticline, and caused or increased the 



Q. J. G. S. Xo. 239. z 



