286 



S. S. BUCKMAN 



[APRIL 



Having captured the Coin, the Severn started an important ob- 

 sequent stream up the valle) r . 



Comparing the obsequent Chelt with the obsequent Frome, it will 

 be seen that the former has done less than the latter, which agrees 

 with the date of capture. The Frome has worked back and captured 

 various consequent streams on the Cotteswold upland ; but the Chelt 

 has not yet done anything in this way. It is in a less advanced stage 

 of obsequent development than the Frome. It should have captured 

 the present head-waters of the Coin, but it has not yet done so. It 

 will do so in time, but by then perhaps the Frome will have got the 

 Churn at Cirencester. 



I had the advantage of visiting the Upper Coin with Professor 

 Davis. He pointed out to me some most instructive phases in its 

 valley development, corresponding with decrease in its volume. There 

 are three valleys. In the upper valley there are meanders of large 



Fig. 9. — Diagram of the phenomena in the Coin valley south of Andoversford. The curves are 

 only very approximate. AAA, curves of upper valley ; B B B, curves of lower valley ; 

 C stream wriggling in its present valley. 



curve, such as a river of large volume would make. In the lower 

 valley the diminished river has been unable to follow the large curves, 

 and it made two turns in each original meander. In the lowest or 

 present valley the river is taking a wriggling course inside the smaller 

 curves. I append a diagram (Fig. 9) to show what has happened ; but 

 it requires a map with contour lines at every 2 5 feet to illustrate clearly 

 such details of river-valley development. 



Diminished river-volume is due to two causes — diminished rainfall 

 and diminished drainage area. Allowing that the former has taken 

 place, yet it will perhaps hardly account for all the phenomena. 1 

 Diminished drainage area is what coincides with the theory set forth. 

 Thus the big curves were cut by the large river, which with its west 

 branch drained the country west of Cheltenham and Gloucester, and by 

 its northern branch — in the Charlton Abbots valley — drained the 

 country north of Winchcomb. The smaller curves w 7 ere cut by the 



1 The so-called pluvial period of post-glacial times will not fit here, except to the details 

 of the lowest valley ; for the date of the upper valley must be Pliocene. 



