16 R. M. Deeley — Glacier Motion. 



III. — Glacier Motion. 

 By R. M. Deeley, M.Inst. C.E., F.G.S. 



SIR HENRY HO WORTH in his Ice or Water deals in considerable 

 detail with the various theories of glacier motion which have 

 been propounded. His works are veritable mines of information 

 concerning the subject of ice and water, and he is everywhere anxious 

 to give all workers credit for the work they have done, to state their 

 theories correctly, and if he should differ from their conclusions to do 

 so in a kindly spirit. Among other theories of glacier motion he 

 refers to the one for which I am responsible. Referring to this 

 theory he says — 1 



"In the Philosophical Magazine for 1888 Mr. Deeley propounded 

 what he claimed to be a new theory of glacier motion. In this 

 paper he very rightly says ' that every change of outline suffered 

 oy a glacier, if we disregard melting and the small internal changes 

 of bulk produced by pressure, etc., is due to the shear of ice plane 

 over ice plane '. He further says of glacier motion : ' "We have, 

 therefore, two kinds of motion — one a bodily slide in a downward 

 direction, and another due to the differential motion of the ice not in 

 contact with the ground.' In order to explain the latter he postulates 

 that constant liquefaction and resolidification is taking place within 

 a glacier by the sun's heat penetrating it and melting certain portions, 

 and inasmuch as a glacier has a tendency to sink in consequence of its 

 gravity, the liquefying of certain portions of its interior will take 

 away the support of the rest and let it sink down. 



" This theory is, as Le Conte says, a modification of Professor James 

 Thompson's. It seems to me to be based on a great many unverified 

 premises. In the first place, the notion that sun heat can penetrate 

 ice and melt small cavities in its interior, forming ice flowers (as was 

 shown experimentally by Tjmdall), may be true of transparent ice, 

 like lake ice, upon which the experiment was tried, but seems to 

 me to be extremely improbable when applied to a glacier with its 

 broken, often snow-covered, opaque or opalescent crust and surface. 

 Again, this process of the sun's heat penetrating a glacier and forming 

 occasional and sporadic ice flowers in its midst would not account for 

 the continuous flow of the whole glacier, whatever effect it might 

 have in inducing isolated particles to move. 



" Thirdly, the theory is based on the notion that glacier ice when it 

 flows is at the melting point, and in fact Mr. Deeley says that it has 

 been experimentally proved that it only moves at this temperature. 

 I altogether traverse the view that anything of the kind has been 

 proved, and the fact that the Alpine, Norwegian, and especially the 

 Greenland glaciers all move in the winter shows it to be untenable. 

 Lastly, and this is conclusive, if the theory were right there would 

 not be a continually increasing differential flow from the base of a glacier 

 to its summit and from its sides towards its centre." 



It must be admitted that this is rather a sweeping condemnation of 

 the theory. I venture to maintain, however, that Sir Henry Howorth 



1 Ice or Water, p. 391. 



