RATE OF DENUDATION 225 



A little consideration will show that in all branches 

 of the investigation of denudation opportunities present 

 themselves on every side of testing, by accurate instru- 

 mental observation and measurement, the rate at which 

 some of the most univeral processes in the geological 

 mechanism of our globe are carried on. 



It has long been a commonplace of geology that the 

 amount of the material removed in suspension and 

 solution by Rivers furnishes a clue to the rate of 

 denudation of the regions drained by the rivers. But 

 how unequal in value, and generally how insufficient 

 in precision, are the observations on this topic ! A few 

 rivers have been more or less systematically examined, 

 some widely varying results have been obtained from 

 the observations, and while enough has been gained to 

 show the interest and importance of the method of 

 research, no adequate supply of materials has been 

 gathered for the purposes of wide, accurate deduction 

 and generalisation. What we need is a carefully organ- 

 ised series of observations carried out on a uniform plan, 

 over a sufficient number of years, not for one river 

 only, but for all the important rivers of a country, and 

 indeed for all the greater rivers of each continent. 

 We ought to know as accurately as possible the extent 

 of the drainage-area of each river, the relations of river- 

 discharge to rainfall and to other meteorological as well 

 as topographical conditions ; the variation in the pro- 

 portions of mechanical and chemical impurities in the 

 river-water according to geological formations, form of 

 the ground, season of the year and climate. The whole 

 geological regime of each river should be thoroughly 

 studied. The admirable report of Messrs. Humphreys 



