126 GEOLOGY [Chap. IX 



Letter 484 Please tell Sir C. Lyell that outside the crater-like 

 mountains at St. Jago, 1 even throughout a distance of two 

 or three miles, there has been much denudation of the older 

 volcanic rocks contemporaneous with those of the ring of 

 mountains. 



I hope that you will not find the page troublesome, and 

 that you will forgive me asking you. 



Letter 485 To C. Lyell. 



[Nov. 6th, 1849]. 

 I have been deeply interested in your letter, and so far, 

 at least, worthy of the time it must have cost you to write it. 

 I have not much to say. I look at the whole question as 

 settled. Santorin 2 is splendid ! it is conclusive ! it is perfect ! 

 You have read Dufr6noy 3 in a hurry, I think, and added 

 to the difficulty — it is the whole hill or " colline " which is 

 composed of tuff with cross-stratification ; the central boss 

 or " monticule " is simply trachyte. Now, I have described 

 one tuff crater at Galapagos (p. 108) 4 which has broken 

 through a great solid sheet of basalt : why should not an 

 irregular mass of trachyte have been left in the middle after 



"... Darwin adopts my views as to Mauritius, St. Jago, and so-called 

 elevation craters, which he has examined, and was puzzled with." — Life 

 of Sir Charles Lyell, Vol. II., p. 158. 



1 The island of St. Jago, one of the Cape de Verde group, is fully 

 described in the Volcanic Islands, Chap. I. 



2 "The Gulf of Santorin, in the Grecian Archipelago, has been for 

 two thousand years a scene of active volcanic operations. The largest 

 of the three outer islands of the groups (to which the general name of 

 Santorin is given) is called Thera (or sometimes Santorin), and forms 

 more than two-thirds of the circuit of the Gulf" {Principles of Geology, 

 Vol. II., Ed. x., London, 1868, p. 65). Lyell attributed "the moderate 

 slope of the beds in Thera ... to their having originally descended the 

 inclined flanks of a large volcanic cone . . . " ; he refuted the theory of 

 " Elevation Craters " by Leopold von Buch, which explained the slope 

 of the rocks in a volcanic mountain by assuming that the inclined beds 

 had been originally horizontal and subsequently tilted by an explosion. 



3 Pierre Armand Dufrenoy published Mhnoires pour servir d utie 

 Description Geologique de la France, as well as numerous papers in the 

 Annales des Mines, Comptes Rcndus, Bulletin Soc Geol. France, and 

 elsewhere on mineralogical and geological subjects. 



4 The pages refer to Darwin's Geological Observations on the 

 Volcanic Islands, etc., 1844. 



