I48 GEOLOGY [Chap. IX 



II. Ice-Action. 

 1841-82. 



Letter 499 To C. Lyell. 



[1841.] 

 Your extract has set me puzzling very much, and as I 

 find I am better at present for not going out, you must let me 

 unload my mind on paper. I thought everything so beauti- 

 fully clear about glaciers, but now your case and Agassiz's 

 statement about the cavities in the rock formed by cascades * 

 in the glaciers, shows me I don't understand their structure 

 at all. I wish out of pure curiosity I could make it out. 



If the glacier travelled on (and it certainly does travel 

 on), and the water kept cutting back over the edge of the ice, 

 there would be a great slit in front of the cascade ; if the 

 water did not cut back, the whole hollow and cascade, as you 

 say, must travel on ; and do you suppose the next season 

 it falls down some crevice higher up ? In any case, how in 

 the name of Heaven can it make a hollow in solid rock, which 

 surely must be a work of many years ? I must point out 

 another fact which Agassiz does not, as it appears to me, 

 leave very clear. He says all the blocks on the surface of 

 the glaciers are angular, and those in the moraines rounded, 

 yet he says the medial moraines whence the surface rocks 

 come and are a part [of], are only two lateral moraines 

 united. Can he refer to terminal moraines alone when he 

 says fragments in moraines are rounded ? What a capital 

 book Agassiz's is. In [reading] all the early part I gave up 

 entirely the Jura blocks, and was heartily ashamed of my 

 appendix 2 (and am so still of the manner in which I 

 presumptuously speak of Agassiz), but it seems by his own 



1 Etudes sur les Glaciers, by Louis Agassiz, 1840, contains a descrip- 

 tion of cascades (p. 343), and " des cavites interieures " (p. 348). 



2 " M. Agassiz has lately written on the subject of the glaciers and 

 boulders of the Alps. He clearly proves, as it appears to me, that the 

 presence of the boulders on the Jura cannot be explained by any dtfbdcle, 

 or by the power of ancient glaciers driving before them moraines. . . . 

 M. Agassiz also denies that they were transported by floating ice." 

 (Voyages of the Adve7iture and Beagle, Vol. III., 1839: Journal and 

 Remarks: Addenda, p. 617.) 



