Vol. 70.] AyyiYERSABY ADDKESS OF THE PRESIDENT. XC'i 



reach alone presents the characteristic form, and evidently there is 

 still much to be done in the middle and lower reaches before such 

 perfection of profile as that of the Severn is attained. 



The power of rivers to roll material doubtless varies in different 

 parts of then- courses according to local circumstances, but the 

 general rule holds good that the upper reaches of English rivers 

 form the scene of erosion, and the lower reaches that of deposition. 

 It would be interesting, in the case of the Exe, to ascertain how far 

 the geological structure is responsible for the imperfection of the 

 gradient ; and secondly, by observing the operations of the river at 

 several points, to determine what progress is being made towards 

 the perfecting of it. I will now merely mention that the whole of 

 the upper part of the course is in Devonian rocks, and that the 

 irregularity in the gradient between 900 and 400 feet may be 

 connected with the character of the strata at Hawkridge. The 

 cessation of the steep gradient at 400 feet marks the spot where 

 the river leaves the Devonian, and flows on to the Culm Measure 

 outcrop. 



In 1906, with the object of determining the rate at which denu- 

 dation is now proceeding and other matters. I commenced an 

 investigation on certain English rivers. The idea was suggested by 

 Sir Archibald Geikie's address to Section C of the British Association 

 at the Dover meeting in 1899, and the investigation has been 

 carried on by the aid of the Royal Geographical Society and of a 

 Government Grant from the Royal Society. 



The investigation necessitated observations under five distinct 

 heads, and for an account of the subdivision of labour among the 

 volunteers who gave their services I must refer you to the reports 

 which have been issued from time to time in the : Geographical 

 Journal " and to the final report on the results, which is now in 

 preparation. The five heads referred to are : — 



(1) The discharge of the rivers. 



(2) The suspended and dissolved impurities in the water. 



(3) The rainfall. 



(4) The area of the river-basins. 



(5) The character of the rocks. 



The objects having a direct geological bearing were a determina- 

 tion of the amount of suspended and dissolved impurities carried 

 yer annum, and a comparison of the conditions observable in rivers 

 draining calcareous and non-calcareous districts, or pervious and 

 impervious formations. 



