R. Russell — On the Flow of Rivers, 8fc. 269 



tenets, as, for instance, the diiferent rates at which the river Niagara 

 has cut its way back from Queenstown Heights to the present situa- 

 tion of the Falls. It has been taken as three feet, one foot, six 

 inches, and one inch per annum, by different computators. Now I 

 do not say that investigations on the river action of the period in 

 which we live will clear up all such anomalies, because these obser- 

 vations will be of more service in estimating the future rate of the 

 wearing down of the materials composing the land than that of the 

 past, as there would always be the difficulty of ascertaining with 

 precision the volume and velocity of the rivers, and the different 

 elevations at which the land was situated at the particular era under 

 consideration ; still it would be a fulcrum on which we might rest 

 the lever of analogy, and raise many questions at present resting in 

 obscurity and doubt into light and certainty. Mr. La Touche 

 will confer a lasting benefit on geological science by continuing 

 these investigations, and still more so by carrying them on with 

 more completeness and accuracy. It would be well to determine the 

 rainfall in the catchment basin from whence the river Onny derives 

 its waters, then knowing the volume of water which is carried away 

 by the river, the ratio of the available rainfall for the purpose of 

 carrying away sediment to the total rainfall may be determined. A 

 system of observations, such as he I'efers to, carried on throughout 

 the whole of Great Britain would be of great value in many respects ; 

 and by means of which the amount of material annually carried to 

 the sea from the different strata which may constitute the basin 

 where the water is collected (such as steep surfaces of granite, gneiss, 

 and slate ; moorland and hilly grounds covered with pasture ; gently 

 undulating and flat cultivated tracts of country), might be obtained. 

 These investigations having been continued for a lengthened 

 period, the estimation of flow in different years, and the amount of 

 sediment brought down might be computed with great exactness in 

 the future, because the discharge and sediment for a number of years 

 having been obtained by means of a series of observations, any one of 

 these years, or a particular portion of one of them, may be used to 

 calculate the greatest, mean, and least discharge for a consecutive 

 number of years, or parts of a year, by multiplying the discharge 

 as formerly obtained by the proportion which the rainfall in those 

 years, or parts of a year, as observed at the standard station, bears 

 to the rainfall at that station during the time that the river was 

 guaged.^ 



As for the different modes by which rivers may be gauged, there 

 are a variety, and the most accurate is by means of the weir gauge ; 

 but it is applicable to small streams only. When a float is used, the 



1 If we suppose that r is the rainfall, d the discharge, and s the sediment, duiing 

 any part of the period when the experiments were conducted ; >•, the rainfall, d^ the 

 discharge, and s^ the sediment, at any future equal length of time, then — 

 r ; r-^^ :: d : di and r ; r^ :: s : s, 



