﻿Correspondence — Mr. Hugh Miller. 41 



we occupy not unlike grounds. Mr. Bonney admits some tarns, like 

 Grasmere, as glacial ; admits, hesitatingly, in part if not wholly, 

 some lakelets, (do these include Grasmere's neighbours?); admits 

 that once a basin is formed, a glacier works in it " under A^ery 

 favourable conditions" (Letter to Mr, Fisher, p. 377), thus granting 

 to the process increasingly favourable conditions ; but demurs to the 

 statement " that though competent to deepen a lake-basin, a glacier 

 could originate it." It would thus seem to be with Mr. Bonne}' 

 a question, not of ability, but of time.'" Did the glacial period last 

 long enough to enlarge, under "very favourable conditions," a tarn 

 it was able to originate under less favourable conditions. 



If I understand Mr. Bonney correctly, we are at one both in our 

 desire to bring each case to the test of observation, and in our ap- 

 preciation . of the increase of theoretical probability as the series 

 advances from tarn to lake. But if the utmost that even his careful 

 observations can do for him is to render the glacial theory probable 

 or improbable (p. 376), then surely these theoretical probabilities 

 are worthy of greater weight than he gives them. His illustrations of 

 blown sand eroding (must we say tarns ?), and Homeric youths spread- 

 ing erratics, seem to me scarcely relevant to the state of the question. 



The latter paragraphs of Mr. Bonney's letter call for no remark 

 from me, as they involve — at this stage — a knowledge of the Alpine 

 lakes that I do not possess. I may assure Mr. Bonney, however, 

 that though I have ventured to remark on his theories, I do not 

 question his facts. 



The letter of my friend Mr. Judd I must attempt — with much 

 diffidence in my own powers — to answer, for it involves destruction 

 to my position. First, let me say a word of explanation. In sup- 

 posing me prepared " to admit the overwhelming probabilities " of 

 the subsidence theory in regard to all the larger lakes, Mr. Judd 

 misunderstands me. A priori probabilities in relation to lakes both 

 large and small, 1 believe must be conceded to both theories. But in 

 such questions, overwhelming probability can be allowed only to 

 overwhelming proof. 



In the second place, as regards the halting-place that Mr. Judd 

 finds between tarns and lakes. If, as I argued, a glacier is a tool 

 that greatly grows in calibre and efficiency as a tarn-hollow en- 

 larges, — that scrapes harder and scores deeper, then to concede 

 tarns to the feebler tool and deny them enlargement by the more 

 powerful, nothing being pointed to as intervening to stop the action, 

 is what may very properly be characterized as not logical and not 

 reasonable. Nevertheless, as for want of standing room and a 

 fulcrum, Archimedes found his theoretically infinitely powerful tool 

 limited by "reasonable proportions" — the limit of all terrestrial 

 tools, so are " reasonable pi"oportions " the limits also of glaciers and 

 their work. While caution then compelled me to remember, and to 

 indicate in my paper, that there are limits to the enlargement of 

 tarns by glaciers, that fact — even in Mr. Judd's able hands — leaves 

 the tarn and lake question precisely on its former basis. 



My friend suggests to me, however, an analogy which may help 



