1844.] ANALOGY OF LAVA STREAMS TO GLACIERS. 43 



VII. SIXTH LETTER on GLACIERS, addressed to the 

 Right Honourable EARL CATHCART.* 



Analogies of Glaciers to Lava Streams Observations on Mount Vesuvius 

 Moraines of Lava Streams Some Objections to the Plastic or Viscous Theory 

 of Glaciers considered Verticality of Crevasses accounted for. 



EOMB, February 5, 1844. 



My Lord In a letter which I addressed to you on the 

 29th ult., I gave some account of the few new observations 

 which untoward circumstances permitted me to make, last 

 autumn, upon the glaciers of Switzerland and Savoy. I have, 

 how r ever, had leisure to reflect maturely upon the theory of 

 glaciers, which I have been occupied for two years in endeavour- 

 ing to mature ; and, without pretending to find in it a complete 

 solution of every problem which might be proposed respecting 

 these wonderful bodies, I am perfectly satisfied that it is funda- 

 mentally conformable to the laws by which they are governed. 

 Some new analogies, to which your Lordship has referred in 

 your last letter, such as that between glaciers and lava streams, 

 may serve to render the subject more popularly intelligible ; and 

 in explaining them, I may have an opportunity of removing, in 

 some degree, the difficulties which have arisen in the minds of 

 candid and intelligent persons, who have studied this theory for 

 the first time difficulties which would probably disappear of 

 themselves by a more prolonged attention. 



I have not had the advantage of seeing the eruption of 

 Etna, to which your Lordship alludes, which was indeed over 

 before I arrived at Naples, and of which I did not even hear 

 for a considerable time after ; so small is the sensation which 

 such events excite in the country. I have, however, had an 

 opportunity probably not less favourable, though far less im- 

 posing of studying the mechanism of plastic lava, in the small 

 currents which, during the months of November and December, 



* Edinburgh New Philosophical Journal, October 1844. 



