1842.] THEORY TO INCLUDE BOTH STRUCTURE AND MOTION. 17 



ticular, is a sort of standing evidence of its mechanism, and, 

 rightly understood, must lead to the most important confirmation 

 of any mechanical theory. This, you may believe, I have made 

 an object of very particular attention. I have now examined 

 so many glaciers as to have a very clear idea of the empirical 

 laws which that structure follows. Lately, I begin to perceive 

 a connection between that structure and the facts of motion 

 already cited. If these two classes of facts can be well brought 

 into harmony with one another, we should have a very good 

 chance of consolidating them into something like a theory. In 

 my next letter, I will give you some account, at all events, of 

 my observations on the subject, which are sufficiently definite, 

 and probably also (without considering it as proved), of what 

 seems likely enough to be its true explanation. I go to-morrow 

 to the Great St. Bernard, to meet M. Studer. Believe me, very 

 sincerely yours. 



IV. THIRD LETTER on GLACIERS, addressed to 

 PROFESSOR JAMESON.* 



The Laws of Structure of Glaciers generally detailed The " Dirt-Bands " described. 

 Mechanical Theory of the Structure Dirt-Bands correspond to Annual Inter- 

 vals Glaciers probably move in Winter. 



ZERMATT, North Side of Monte Eosa, 

 22d August 1842. 



My Dear Sir I arrived here two days ago by a very 

 interesting and unfrequented route. I mentioned in my last, 

 that M. Studer and I had agreed to visit together the valleys 

 eastward of the great St. Bernard. The Convent was our 

 place of rendezvous, and we afterwards descended to Orsieres, 

 and turned into the valley of Bagnes. Crossing the Alpine 

 chain at the head of the valley, by the Col de Fenetres, we 

 went down to Valpelline on the Italian side, and ascended that 



* Edinburgh New Philosophical Journal, October 1842. 

 C 



