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S. S. BUCKMAN 



U.PRIL 



Ogbourne gorge, in the Chalk to the south of Swindon towards Marl- 

 borough, along which runs the Roman road from Cirencester to 

 Winchester. 



III. The valley contains a divide from which the floor slopes both 

 ways : it holds two streams — one flowing with the dip and one against 

 (Fig. 3). Examples : — The pass from Cheltenham to Andoversford ; 

 the pass from Winchcomb to Andoversford ; the Moreton valley. 



IV. The valley contains an antidip stream only. Example : — The 

 Stroud valley. 



V. The valley opens headward high above the plain ; it only con- 

 tains a stream in its lower part, if at all. Examples :— More or less 



' '-BnocAhamlito 



Fig. 4. — Opposition of obsequent and subsequent, and obsequent and consequent, streams near 



Winchcomb. Scale 1"=1 mile. 



dry valleys extending back from the Cotteswold escarpment — a valley 

 leading from above the Vale of Pewsey to the Kennet, in which runs 

 a road from Marlborough to Alton Priors. 



To consider the development of these valleys and the escarpment 

 breaches to which they give rise. I. This is due to the cutting down 

 by a consequent stream in the ordinary course of events. II. is due 

 to the same cause ; but there is a later phase : the original excavating 

 stream has been tapped and diverted before reaching the gorge. III. 

 This is a further development of II. An obsequent stream has been 

 started, which excavates the original valley-floor of the consequent 

 stream, farther and farther back. This type is found in all stages of 

 development up to IV, in which the original consequent stream has 

 been nearly driven out of its valley, and the valley-floor has been 

 trenched nearly to the mouth of the original valley. 



The first type of valley holds a through stream now. The 

 others are considered to have held through streams formerly. Where- 

 fore when they are recognised, such through streams may be given 

 them in river restoration, and according to the relative depths to 

 which the cutting of the original valley-floor has been carried out, so 

 may the further stage of river development be surmised — whether a 

 stream captured its neighbour before it was captured itself, and so forth. 



