J, W. Judd — On Vokanos, 15 



ranean forces, in directing, controlling and modifying the effects 

 produced by denuding agencies, that any difficulty has ever been 

 experienced in accounting for the formation of lakes, or that the 

 necessity is felt for assuming that rivers of ice possess a power, 

 which it is on all hands admitted does not belong to rivers of loater 

 — that of excavating great basin-shaped depressions in their course. 

 To those who believe that — alike in the present and during all 

 former geological periods — the subterranean and subaerial agencies 

 have been in unceasing action, side by side, and that the present 

 features of the earth's surface are the result of the constant mutual 

 interaction of these two classes of forces — the formation of rock- 

 basins, far from being, as is asserted, an abnormal phenomenon, is 

 one of the necessary consequences of the antagonistic agencies which 

 we can demonstrate to be operating on the surface of our planet. 

 If it be granted, in the first place, that meteoric agencies have the 

 power of producing great lines of drainage (valleys) on the earth's 

 surface — and, in the second place, that different portions of such lines 

 of drainage may be subjected to unequal vertical movement — and 

 of the truth of both these postulates we can produce equally unmistak- 

 able and convincing evidence — then it follows, inevitably, that cascades 

 or rapids on the one hand, and lake-basins on the other — the results 

 of converse relations of the two sets of forces — must he from time to 

 time produced in these lines of drainage. And if all the existing 

 lake-basins are to be assumed to have been produced by ice-erosion, 

 we may surely be justified in asking — What has become of those 

 which must have resulted from the action of the obvious causes to 

 which we have just referred ? 



To sum up the argument of the present chapter — We have demon- 

 strated that the basins of the largest lakes in our own islands, in the 

 Alpine regions of Europe, and in equatorial Africa, respectively, 

 could not possibly have been formed by the supposed excavating 

 power of ice. We have also shown that in each of these cases there 

 is the strongest ground for believing the districts in question to have 

 been subjected to powerful subterranean movement ; and that these 

 were quite competent to produce the depressions in question. 



But if it can be proved that in the case of lakes which happen to 

 preserve evidences of the manner and date of their origin, the 

 ordinary operations of denuding and subterranean forces are quite 

 competent for their production — even when the lakes are of the very 

 largest dimensions — where is the necessity for calling in the aid of a 

 new and problematical agency to account for the formation of the 

 smaller examples ? 



For ourselves, we must add — in the face of the strenuous efforts 

 which have recently been made to resuscitate the doctrine of the 

 erosion of lake-basins by ice — that an attentive study of the lakes of 

 both the Scottish Highlands and of the Alps (districts which have 

 been so confidently appealed to as affording the strongest support to 

 the theory) has only served to confirm our conviction in the justice 

 of the conclusion, on this subject, that has been arrived at by all 

 except an inconsiderable minority of geologists — namely, that the 

 agency in question is as unnecessary as it is hypothetical. 



