142 GEOLOGY [Chap. IX 



Letter 493 examples for you, as there then can be no coral mud to 

 depress the bottom? In my Volcanic Islands,^. 126, I just 

 suggest that volcanoes may occur so frequently in the oceanic 

 areas as the surface would be most likely to crack when 

 first being elevated. I find one remark, p. 128, 1 which seems 

 to me worth consideration — viz. the parallelism of the lines 

 of eruption in volcanic archipelagoes with the coast lines of 

 the nearest continent, for this seems to indicate a mechanical 

 rather than a chemical connection in both cases, i.e. the lines 

 of disturbance and cracking. In my South American Geology \ 

 p. 185, 2 I allude to the remarkable absence at present of 

 active volcanoes on the east side of the Cordillera in relation 

 to the absence of the sea on this side. Yet I must own I 

 have long felt a little sceptical on the proximity of water 

 being the exciting cause. The one volcano in the interior 

 of Asia is said, I think, to be near great lakes ; but if lakes 

 are so important, why are there not many other volcanoes 

 within other continents ? I have always felt rather inclined 

 to look at the position of volcanoes on the borders of conti- 

 nents, as resulting from coast lines being the lines of 

 separation between areas of elevation and subsidence. But 

 it is useless in me troubling you with my old speculations. 



T , „ To A. R. Wallace. 



Letter 494 



March 22nd [1869]. 



The following extract from a letter to Mr. Wallace refers to his 

 Malay Archipelago, 1869. 



I have only one criticism of a general nature, and I 

 am not sure that other geologists would agree with me. 



crack in its weakest spot, the heavy side going down, and the light side 

 rising." In discussing this view Lyell writes {Principles, Vol. II. 

 Ed. X., p. 229), " This hypothesis appears to me of very partial appli- 

 cation, for active volcanoes, even such as are on the borders of continents, 

 are rarely situated where great deltas have been forming, whether in 

 Pliocene or post-Tertiary times. The number, also, of active volcanoes 

 in oceanic islands is very great, not only in the Pacific, but equally in the 

 Atlantic, where no load of coral matter .... can cause a partial 

 weighting and pressing down of a supposed flexible crust." 



1 Volcanic Islands, p. 128 : "The islands, moreover, of some of the 

 small volcanic groups, which thus border continents, are placed in lines 

 related to those along which the adjoining shores of the continents 

 trend " [see fig. 5]. 



3 Geological Observations on South America, London, 1846, p. 185. 





