1841—1882] noN 



To C Lyell. Uum 5 ° 7 



n, Sept. 8th [i> 



Many thanks for the pamphlet, which was returned this 

 morning. I was very glad to read it, though chiefly as a 

 psychological curiosity. I quite follow you in thinking 

 Agassiz glacier-mad. 1 His evidence reduces itself to sup- 

 posed moraines, which would be difficult to trace in a 

 forest-clad country ; and with respect to boulders, these are 

 not said to be angular, and their source cannot be known 

 in a country so imperfectly explored. When I was at Rio, 

 I was continually astonished at the depth (sometimes 100 ft.) 

 to which the granitic rocks were decomposed in situ, and this 

 soft matter would easily give rise to great alluvial accumula- 

 tion-; ; 1 well remember finding it difficult to draw a line 

 between the alluvial matter and the softened rock in situ. 

 What a splendid imagination Agassiz has, and how energetic 

 he is ! What capital work he would have done, if he had 

 sucked in your Principles with his mother's milk. It is 

 wonderful that he should have written such wild nonsense 

 about the valley of the Amazon ; yet not so wonderful when 

 one remembers that he once maintained before the British 

 Association that the chalk was all deposited at once. 



With respect to the insects of Chili, I knew only from 

 Bates that the species of C ambus showed no special affinity 

 to northern species ; from the great difference of climate and 

 vegetation I should not have expected that many insects 

 would have shown such affinity. It is more remarkable that 

 the birds on the broad and lofty Cordillera of Tropical S. 

 America show no affinity with European species. The little 

 power of diffusion with birds has often struck me as a \v. st 

 singular fact — even more singular than the great power of 



1 Agassiz's pamphlet 1 of the Am is referred to by Lyell 



in a letter written to Bunbury in September, 1866 / 

 Lyell^ II., p. 409): "Agassiz has written an interesting paper on the 

 'Geology of the Amazons,' but, I regret to say, he has gone wild about 

 glaciers, and has actually announced his opinion that the whole of the 

 great valley, down to its mouth in hit. o , was filled by ice. . . 

 Agassiz published a paper, "Observations Geologiques faites dans la 

 Vallee de FAmazone," in the Comptes Rendus, Vol. LXIV.. p. 1269, 1 

 See also a letter addressed to M. Marcou, published in the Bull. S 

 Ceol. France. Vol. XXIV., p. 100. 1S66. 



