82 VISCOUS THEORY OF GLACIER MOTION. [1845 



theoretical views have admitted to be a correct statement of 

 the facts.* 



My attention was at that time (March 1843) turned by my 

 learned and acute friend, Mr. W. A. Cadell, to the veined struc- 

 ture of the slag of iron furnaces as due to the difference of 

 velocity of the parts producing surfaces of separation and peculiar 

 molecular condition. The transition was easy to the case of 

 volcanic rocks and lava streams ; and this case was pressed on 

 my attention by an unexpected journey which I soon after 

 undertook to Italy and Sicily. 



2. ANALOGY OF GLACIERS TO LAVA STREAMS. 



There is something pleasing to the imagination in the 

 unexpected analogies presented by a torrent of fiery lava and 

 the icy stream of a glacier. But when we look upon the com- 

 parison historically and critically, and find how generally this 

 analogy has been perceived and adverted to by persons of very 

 different views and talents of observation, we are strongly 

 tempted to suspect that some latent cause confers the marked 

 resemblance. 



This cause I of course consider to be the laws and condition 

 of their motion, the struggle of a semi-fluid mass of enormous 

 weight creeping down a mountain side, in which fluidity and 

 solidity are so curiously combined, that we should be at a loss 

 in either case how to name it ; a straining, crackling, splinter- 

 ing solid, heaved on by the internal energy of the latent 

 fluidity which pervades it, and which at last succeeds in 

 giving to the general character of the motion and the moving 

 mass, those of fluid bodies subject to the law of gravity ; 

 whilst the parts, themselves almost rigid, have that rigidity 

 most fantastically subjected to the action of the dominant 

 principle. 



In illustration of what has now been said, I shall quote 

 passages from some authors which, without particular research, 



* Bibliotheque Universelle, tome xliv. p. 153. " C'est en effet un fait assez 

 general que les bandes bleues coupent a angle droit les crevasses," etc. 



