144 GEOLOGY [Chap. IX 



Letter 494 You repeatedly speak as if the pouring out of lava, etc., 

 from volcanoes actually caused the subsidence of an adjoining 

 area. I quite agree that areas undergoing opposite move- 

 ments are somehow connected ; but volcanic outbursts must, 

 I think, be looked at as mere accidents in the swelling up 

 of a great dome or surface of plutonic rocks, and there seems 

 no more reason to conclude that such swelling or elevation in 

 mass is the cause of the subsidence, than that the subsidence 

 is the cause of the elevation, which latter view is indeed held 

 by some geologists. I have regretted to find so little about 

 the habits of the many animals which you have seen. 



Letter 495 To C. Lyell. 



Down, May 20th, 1869. 



I have been much pleased to hear that you have been 

 looking at my S. American book, 1 which I thought was as 

 completely dead and gone as any pre-Cambrian fossil. You are 

 right in supposing that my memory about American geology 

 has grown very hazy. I remember, however, a paper on the 

 Cordillera by D. Forbes, 2 with splendid sections, which I 

 saw in MS., but whether " referred " to me or lent to me I 

 cannot remember. This would be well worth your looking 

 to, as I think he both supports and criticises my views. In 

 Ormerod's Index to the Journal, 3 which I do not possess, 

 you would, no doubt, find a reference ; but I think the 

 sections would be worth borrowing from Forbes. Domeyko 4 

 has published in the Comptes Rendus papers on Chili, but not, 

 as far as I can remember, on the structure of the mountains. 



1 Geological Observations on South America, London, 1846. 



2 " Geology of Bolivia and South Peru," by Forbes, Quart. Journ. 

 Geol. Soc, Vol. XVII., pp. 7-62, 1861. Forbes admits that there is "the 

 fullest evidence of elevation of the Chile coast since the arrival of the 

 Spaniards. North of Arica, if we accept the evidence of M. d'Orbigny 

 and others, the proof of elevation is much more decided ; and conse- 

 quently it may be possible that here, as is the case about Lima, according 

 to Darwin, the elevation may have taken place irregularly in places ..." 

 (Joe. eit., p. 11). 



3 Classified Index to the Transactions, Proceedings and Quarterly 

 Journal of tlui Geological Society. 



4 Reference is made by Forbes in his paper on Bolivia and Peru to 

 the work of Ignacio Domeyko on the geology of Chili. Several papers 

 by this author were published in the Annates des Mines between 1840 

 and 1869, also in the Comptes Rendus of 186 1, 1864, etc. 



