﻿42 Correspondence — Mr. Hugh Miller. 



it on, and aid me to show the fallacy of the analogy by which he 

 seeks to undermine some of the grounds 1 occupy. Every one who 

 has studied streams and rivers knows that below rapids and falls, 

 and at other places, they scoop pools much deeper, and also broader, 

 than the average stream near the place. The little runnel makes a 

 rough dimple ; the Highland burn a linn ; the alluvial river leaves 

 in its old channels small meres ; and in the valley of the gi'eat 

 Amazon these isolated pools are represented by lakelets or lakes 

 some ten miles long, roughly speaking, and thirty or forty feet deep. 

 The rule is, that the volume of the stream determines the size and the 

 contents hy volume of the pooh it mahes. Glancing back now to the 

 question of "reasonable proportions," it is evident that this rule 

 must not be unreasonably stretched by a use of blind logic. To say 

 that it applies within reasonable limits, is correct ; to say that any 

 one allowing only the pools of the burn to the large river is illogical 

 (as well as wrong) is also correct. But to repudiate the rule because 

 it cannot explain lakes proportioned by their size to the hypothetical 

 pools of impossible rivers, would be simply futile. 



But I proceed to apply this rule elsewhere. Mr. Judd refuses to 

 allow that a glacier grinds in a basin with added force, on the grounds 

 that "we are led to infer" that streams of water and rivers of ice fall 

 under similar laws of motion (p. 525), and in a preceding paragraph 

 (p. 524) he says what must involve belief on his part, in the pro- 

 duction by glaciei'S of basins proportional in superficies to the pools 

 of the Highland burn and Mississippi river. The above rule, that 

 streams of water make their pools according to their volume, being 

 correct, rivers of ice, Mr. Judd will probably admit, should do like- 

 wise. Now streams very much broader than the Amazon do not, 

 and probably could not exist, though I am safe in saying that if they 

 did their pools would be lakes. But it is a truism now-a-days that 

 glaciers many times wider than the Amazon did and do exist. The 

 Humboldt glacier is about 60 miles wide ; ancient glaciers moved 

 over plateaux and over-rode watersheds, and by the analogy claimed 

 by Mr. Judd we would be justified — nay, encouraged— in predicating 

 as possible lakes limited in breadth only by the volume of glacier 

 and ice-sheet. It is not immoderate then to ask for the sprinkling of 

 tarns and lakes which the nature of the pre-glacial surfaces favoured. 



Although, as I think, legitimately damaging to Mr. Judd's position, 

 his parallel between ice and water cannot strictly be carried out. 

 The cascade of a Highland burn tumbles into a pool less broad some- 

 times than deep, and not much longer. To accredit glaciers with 

 such powers were to forget an important element of difference — the 

 greater rigidity of ice. It is this property — the same that makes 

 glaciers habitually scratch rocks as well as smoothing them, thus 

 giving them a greater rock-hollowing power — that has made it 

 possible for me to argue, what could not be argued of water, that 

 the deeper a glacier drives a basin, " the more fully it feels its 

 power and the more easily and rapidly it works." 



A word now upon the stratigraphical division of the question. 

 With deference to Mr. Judd's authority, I must say that 1 cannot 

 agree with him that the horizontality of the Assynt mountains is "an 



