XC PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 1914, 



which traverses outcrops of easily recognizable rocks should give a 

 clue to the distance over which the coarser debris is being trans- 

 ported, due regard being paid to the fact that calcareous rocks are apt 

 to disappear by reason of their solubility. My impression, founded 

 on limited observations, is that in the majority of English rivers the 

 distance is trifling as compared with the length of the river. 



Few rivers roll material directly into the sea ; in fact, no English 

 river is now accomplishing this feat. The conditions for its accom- 

 plishment involve a continuously steep gradient down to tide-level. 

 In our rivers the steep gradient is generally confined to the upper 

 reaches ; a modified gradient, with correspondingly reduced trans- 

 porting power in the current, characterizes the middle reaches ; 

 while in the lower reaches transportation is replaced by deposition. 

 This condition is due partly to the fact that the riv r er-systern has 

 gone far towards reaching what is known to physiographers as 

 * maturity,' but still more to the sinking of the land which has 

 taken place during and since Neolithic times, and has had the 

 effect of drowning the lower reaches and admitting the tide far 

 inland. A restoration of the land to the level recorded in the 

 Neolithic deposits of the Barry and Southampton Docks and in the 

 buried peat-beds of many other estuaries, would go far towards 

 excluding the tide from the lower reaches ; but a further elevation 

 would be required to bring about that ' rejuvenescence ' which 

 would render our rivers capable of carrying their coarser solid 

 contents clear out to sea. 



The diagram of the Exe, the Medway, and the Severn facing this 

 page illustrates two types of English river. The points of inter- 

 section of the river-bed with the contours shown on the Ordnance 

 maps are plotted at their proper respective distances from the 

 source, the scales being so adjusted as to give a vertical exag- 

 geration of about 105. The Medway and the Severn show a 

 profile which may be taken as typical of English rivers. Tidal 

 waters extend about a third of the total length of the river. A 

 long stretch of gentle gradient follows, increasing in steepness 

 steadily, but with almost imperceptible slowness. Then comes a 

 sudden curve up to the source. Such profiles tell their own tale. 

 Whatever rapids or waterfalls may once have existed, all have eaten 

 their way back to form part of the upper and steeper reaches, 

 leaving behind them an evenly graded channel. In the Exe the 

 case is different ; the tidal reach is comparatively short, the middle 

 reach is not only steeper, but is not perfectly graded. The upper 



