M. A. de la Rive on Glaciers. 1^)5 



Concerning the Successive Appearance and Disappearance of 

 Great Glaciers upon the present surface of the Terrestrial 

 Globe. Extract of a Letter from M. A. DE LA RiVE to 

 M. Arago. 



The communications which M. Constant Prevost has pre- 

 sented to the Academic des Sciences, upon the appearance, the 

 diminution, and the disappearance, of glaciers, have recalled to 

 my recollection that, in the year 1845, 1 ventured to express 

 an opinion on the subject, which, to a great extent, corres- 

 ponds with that of M. Prevost. The occasion was presented 

 in the course of the discussion elicited by the researches of 

 M. Agassiz, concerning the origin of boulders, which the 

 learned geologist communicated to the Helvetic Society of 

 Natural History, during its meeting at Geneva. The notice 

 •of M. Prevost has afresh excited my attention to this question 

 of glaciers, and I flatter myself that I have succeeded in elu- 

 cidating it in a satisfactory manner ,'so perfecting those ideas 

 which I had only orally announced in 1845. The following 

 is a sketch of them : — 



Along with M. Prevost, I do not think it at all necessary to 

 inquire elsewhere than in present existing causes for the 

 explanation of the successive appearance and disappearance 

 of great glaciers upon the existing surface of our globe. I 

 am satisfied with starting from a fact which is not only in 

 harmony with the best established theories of physical science, 

 but which, moreover, is confirmedby direct observations, and 

 which maybe thusexpressed, — That in mountainous countries 

 especially, humidity is accompanied, at all times, by a very 

 decided diminution of temperature. To which is to be added, 

 that when the emersion of the European soil was effected, 

 the strata of the most recent formation, still anterior however 

 to the appearance of the glaciers, must needs have been im- 

 l)regnated with a considerable quantity of water, since pre- 

 viously they had always been submerged. Great evapora- 

 tion then would necessarily be the consequence, whence would 

 result vast downpours of rain, and consequently a consider- 

 able fall of temperature. These two causes united, — on the 



