L. Ridiardsoii — River Development in Wales. 509 



developed by Mr. S. S. Buckman and others, these views have met 

 with much support, and certainly have the advantage of explaining 

 many otherwise unintelligible phenomena. 



In brief, as far as the Lower Severn Valley is concerned, the 

 exponents of this theory hold that the valley of the Lower Severn Avas 

 once non-existent ; that the beds now terminating in the Cotteswold 

 escarpment once extended much further west, up to, if not beyond, 

 the borderland of the Palfeozoic rocks. And not only did these 

 rocks extend much further west and fill up the present Lower 

 Severn Valley, but other deposits of great thickness also passed 

 westwards above them. These Neozoic rocks were doubtlessly 

 uplifted to form a great coastal plain gently sloping to the south- 

 east. Over it the initial drainage ran in channels, usually, as one 

 would expect, with an approximate direction from north-west to 

 south-east. These original consequent- streams followed the ordinary 

 course of river-development, deepening their channels, developing 

 subsequents, capturing, and being captured. 



Slowly and surely, however, whilst this development was proceeding, 

 the theory has it that the Severn was cutting its way backwards 

 from the south-west, capturing the transfluent consequent-streams 

 one after the other, diverting the waters to the west of the elbows 

 of capture into its own channel, and causing the beheaded streams 

 to take their rise at some point to the east of the place of capture. 

 In this way a divide was initiated between the capturing river and 

 the beheaded streams. Thus had the Cotteswold escarpment its 

 genesis, and as obsequent-streams were developed in the old con- 

 sequent notches immediately to the east of the points of capture, it 

 was caused to proportionately retreat. Further development has 

 produced the mature valley of the Lower Severn, Avith its fault-block 

 hills of Bredon and Woolstou, the butte-like Churchdown Hill, 

 the conical Robins' -Wood Hill, and the cuesta of the Cotteswolds. 

 Away to the south-east, clearly visible from manj^ of the eminences 

 of the Cotteswold Hills, stretches the white Chalk escarpment. 



In the heart of Wales, centred round Builth Wells, the present 

 river-systems are in a prior phase of development of a subsequent 

 cycle to that which has been reached in Gloucestershire and the 

 adjacent counties. In many parts of Wales, as is so well seen from 

 the Arans and Cader Idris, the rejuvenated rivers are actively 

 engaged in dissecting the well-known peneplain. The case is not 

 absolutely parallel, of course, although it sufficiently approximates 

 to merit comparison. Standing on such a hill as Y Foel, north of 

 Llanwrtyd Wells, and looking toward the south-east, one sees the 

 channelled escarpment of the Wenlock and Ludlows, capped with 

 the basement-beds of the Old Red Sandstone, which has been pictured 

 so well by Murchison. The combes are not much more than storm- 

 channels. They are not like the more mature combes of the Mid- 

 Cotteswolds, for they are in a prior phase of development. From 

 the Mynydd Bwlch-Y-Groes flows the Dulas River north-westward 

 to the Irfon, which continues to flow in the same direction along 

 the foot of the great Mynydd Eppynt to join the Wye near Builth. 

 The Mynydd Eppynt declines to the south-east, and is drained by 



