Vol. 60.] THE VALLEY OF THE TEIGN. 331 



and Clifford Bridge was originated bv one of these tributaries 

 running off the slope of a ridge then connecting Mardon Down 

 with East Down, it seems quite possible that by the gradual 

 detrition of the country this ridge might be reduced to a low col or 

 pass leading from the tributary of the Lower Teign to the valley of 

 the Upper Teign, the latter river flowing at a considerably higher 

 level than the former. Under these circumstances a temporary 

 obstruction in the valley of the Upper Teign, such as might be 

 caused by a landslip, or a sudden rise of the river caused by heavy 

 rains, might easily send its waters over the col and into the Lower 

 Teign ; and whenever this happened, the new course would probably 

 become the permanent one. because it led down to a lower level. 

 Such a method of ' capture' has been accepted as an explanation of 

 alteration in the course of the Trent and in many other cases. 



If the valley of the Teign Estuary was solely the work of the 

 Lemmon and its tributaries, including the Bovey and the above- 

 mentioned Lower Teign, they would be quite equal to the task of 

 keeping it open, provided that the production of the Bovey syncline 

 was accomplished slowly, so that the rate of river-erosion could 

 keep pace with that of the relative vertical displacement. 



As stated on p. 328, it is probable that the volume and power of 

 the Lemmon was materially augmented by the accession of the river 

 Yeo, then flowing along the line of the Kester Brook ; for this 

 would add another head of water from the high ground of Dart- 

 moor. If this was so, then the diversion of the Yeo into the Valley 

 of the Dart is a much more recent event than the diversion of the 

 Upper Teign into its present course ; for, what seem to be the latest 

 stages of its accomplishment still remain well marked on the 

 geography of the country, and thus afford an illustration of the 

 manner in which the Lower Teign may have captured the Upper 

 Teign. 



West of Ashburton the Yeo now passes through quite a narrow 

 cut between two hills which are higher than any of the surrounding 

 land, one of them rising to over 500 feet : and these hills look as if 

 they were remnants of a ridge that once extended right across the 

 Ashburton Vallev from north-west to south-east. It is certain, at 

 any rate, that if the high ground south-east of Ashburton were 

 united to Dartmoor by such a ridge at the present time, and if its 

 lowest part were not less than 400 feet above Ordnance-datum, the 

 Biver Yeo would at once be diverted into the valley of the Kester 

 Brook (see fig. 3, p. 329). There is, consequently, some ground for 

 the remark that the present features of the district harmonize very 

 completely with the theory that the head- waters of the Yeo have 

 been transferred from one valley to the other. 



Let us imagine the Yeo flowing as I have supposed, and the Dart 

 running more or less in its present valley, and of course cutting 

 down to a much lower base-level than the Yeo. So long as the 

 general slope was easterly no change would be likely to occur, and 

 the Yeo would continue to deepen the valley through which it ran, 

 the final form of which now remains in that of the Kester Brook. 



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