466 Notices of Memoirs — British Association — 



data determined by accurate, systematic, and prolonged measure- 

 ment as would alone furnish a satisfactory basis for computations 

 of the rate at which denudation takes place. Some instrumental 

 observations of the greatest value haye indeed been made, but for 

 the most part observations of this kind have been too meagre and 

 desultory. 



A little consideration will show that in all branches of the 

 investigation of denudation opportunities present themselves on 

 every side of testing, by accurate instrumental observation and 

 measurement, the rate at which some of the most universal processes 

 in the geological regime 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 obtained 

 to show the interest and importance of the method of research, no 

 adequate supply of materials has been gathered for the purposes of 

 accurate deduction and generalization. What we need is a carefully 

 organized 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 proportions 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 

 and Abbot, on the "Physics and Hydraulics of the Mississippi," 

 published in 1861, might well serve as a model for imitation, 

 though these observers necessarily occupied themselves with some 

 questions which are not specially geological and did not enter into 

 others on which, as geologists, we should now gladly have further 

 information. 



Again, the action of Glaciers has still less been subjected to 

 prolonged and systematic observation. The few data already 

 obtained are so vague that we may be said to be still entirely 

 ignorant of the rate at which glaciers are wearing down their 

 channels and contributing to the denudation of the land. 



The whole of this inquiry is eminently suitable for combined 

 research. Each stream or glacier, or each well-marked section of 

 one, might become the special inquiry of a single observer, who 

 would soon develop a paternal interest in his valley and vie with his 

 colleagues of other valleys in the fulness and accuracy of his records. 



Nor is our information respecting the operations of the Sea much 

 more precise. Even in au island like Great Britain, where the 



