Prof. Forbes on Ice and Glaciers. 199 



credit. Professor Thomson, or some one who maintains the 

 same opinion which he does, will, I have no doubt, be ready and 

 willing to give grounds for his judgement. 



Why 1 very reluctantly appear in the matter is for this I'eason 

 — that I believe you have not altogether understood, perhaps 

 have overrated, what I claim to have established, particularly in 

 connexion with the change admitted by all parties to have 

 occuiTcd in some of my ideas, in consequence of my journey in 

 1846, described in the Thirteenth Letter before mentioned. 

 Several passages at pages 95 and 96 of your paper seem definitely 

 to indicate that you ascribe to me an abandonment of a pre- 

 viously elaborate theory of the cause of the Veined Structure, 

 and the substitution of a theory subversive of, and superseding 

 in all points the old one. I will cite only one passage, including 

 a quotation from myself, as given at p. 95 of your paper. It is 

 as follows : — 



" ' Mr. Hopkins,' writes Professor Forbes in 1845, in refer- 

 ence to an experimental proof, ' denies that the ribboned 



(veined) structure is produced by differential motion No 



person who has seen the model made, or even been told how it was 

 made, and inspects the ribboned structure upon its surface, can, I 

 think, unless influenced by previous theoretical views, entertain 

 any other opinion,' Is it to be supposed that convictions thus 

 strongly uttered, based upon years of observation, and esta- 

 blished, according to the above quotation, by the testimony of 

 the senses themselves, are meant to be reversed by a single ob- 

 servation, which, after all, is essentially defective, involving, in 

 reality, not a fact, but an opinion ? " 



The italics are yours. Here I am repi'esented as stating a 

 theory of the veined structure in 1845, which, it is argued, I 

 could not (as I am represented to have done) have relinquished 

 in merely one or two sentences of a letter of 1846. I shall 

 probably give you satisfaction when I assure you that the doc- 

 trine of the origin of the veined structure, so far as described in 

 the preceding citation, and in several other passages of those 

 pages of your article already i-eferred to (pp. 95 and 96), was 

 neither given up by me in 1846, nor in any subsequent year — 

 nay, that I hold it still. I also entertain the very same views 

 with reference to Mr. Darwin's theory of banded lavas which 1 

 did in 1845, which at page 96 you understand me to have 

 abandoned, or at least that I am lepresented to have abandoned 

 them, in 1846*. 



[* For tlie sake of clearness, I hope I may be permitted to state that the 

 asmmption to which I referred is expressed by Mr. Darwin in the following 

 words : — " In the ice the porous lamina: are rendered distinct by the sub- 

 sequent congelation of infiltrated water;" and my statemcut is, that 



