SECTIONAL TRANSACTIONS— E. 347 



Wednesday, September 6. 



Mr. A. Austin Miller. — The physiographic evolution of the lower Wye 

 valley. 



The meanders of the river Wye were developed on a surface of post- 

 Liassic age, but of this surface no relics can be identified with certainty. 

 During the process of dissection of this stage the river reached maturity at a 

 height of about 500 ft. above the present river-bed, and produced an exten- 

 sive peneplain at this level, into which the river is remarkably entrenched. 

 A third phase of still-stand at about 200 ft. above present level is indicated 

 by the preservation on several spurs and meander-cores of bevelling at this 

 altitude. The river is now entrenching itself into this stage. 



The two latter stages are tentatively correlated with fairly well-defined 

 platforms of marine denudation on the north shore of the Severn Estuary 

 at about 400 ft. and 150 ft. respectively, which are briefly examined. 



In the process of adjustment the river has effected minor changes in its 

 course and abandoned some entrenched meanders at diflferent levels. 



Mr. D. L. Linton. — Some aspects of the physiography of southern Scotland. 



Thirty years ago Mackinder put forward the thesis that in the south- 

 eastward-flowing portions of certain Scottish rivers we may see the remnants 

 of an original consequent drainage system whose streams flowed con- 

 tinuously from the Minch to the Scottish Border. In doing so he realised 

 that such eastward-flowing streams as the Aberdeenshire Dee and Don, 

 the Tummel, the Earn, the Forth, and the Tweed found no place in this 

 scheme, but he did not therefore abandon it. Later workers adopted this 

 idea completely. Mort suggested an Argyllshire source for the Galloway 

 rivers ; Gregory found no difficulty in carrying a reversed Lower Clyde 

 eastwards to the North Sea at Berwick ; Peach and Home found themselves 

 forced to draw conclusions as to the origin of the Tweed not in accord with 

 the accepted principles of river development. 



This preconception as to the nature of the river system from which the 

 present Scottish drainage has developed, led in the southern uplands to a 

 failure to realise two important points. The first is the very great extent 

 to which the original drainage has been modified by the growth of sub- 

 sequent streams. The second is that in addition to the classes of streams 

 already recognised in the region, viz. : 



(a) the south-eastward or south-south-eastward-flowing streams, such 

 as the Nith and the Gala, of supposed consequent origin ; 



(6) the unexplained east-flowing Tweed, matched by the Forth and 

 the South Tyne just beyond the limits of the region ; 



(c) the subsequent streams such as Ettrick and Yarrow, 



there exists an important series of right-bank tributaries to the Tweed 

 flowing from south-south-west to north-north-east. 



In the present communication evidence is brought forward to show 

 that the Tweed must be regarded — together with similar major east- 

 flowing rivers — as a consequent trunk stream, receiving both left- and 

 right-bank consequent tributaries, of which the Gala and Jed are types. 

 Further south a second series of minor consequents flowing south-south- 

 east and including the Nith, Esk, and Rede, were received as left-bank 

 tributaries by the east-flowing Tyne, while to the north the Forth had a 

 similar origin and function. 



