18401881] EARTH-MOVEMENTS 127 



the explosion and emission of mud which produced the Letter 485 

 overlying tuff? Or, again, I see no difficulty in a mass of 

 trachyte being exposed by subsequent dislocations and bared 

 or cleaned by rain. At Ascension (p. 40), subsequent to 

 the last great aeriform explosion, which has covered the 

 country with fragments, there have been dislocations and a 

 large circular subsidence. . . . Do not quote Banks' case l 

 (for there has been some denudation there), but the <( elliptic 

 one " (p. 105), which is 1,500 yards (three-quarters of a 

 nautical mile) in internal diameter . . . and is the very one 

 the inclination of whose mud stream on tuff strata I measured 

 (before I had ever heard the name Dufrenoy) and found 

 varying from 25 to 30. Albemarle Island, instead of being 

 a crater of elevation, as Von Buch foolishly guessed, is formed 

 of four great subaerial basaltic volcanoes (p. 103), of one of 

 which you might like to kno\v the external diameter of the 

 summit or crater was above three nautical miles. There are 

 no " craters of denudation ' at Galapagos. 2 



I hope you will allude to Mauritius. I think this is the 

 instance on the largest scale of any known, though imperfectly 

 known. 



If I were you I would give up consistency (or, at most, 

 only allude in note to your old edition) and bring out the 

 Craters of Denudation as a new view, which it essentially is. 

 You cannot, I think, give it prominence as a novelty and yet 

 keep to consistency and passages in old editions. I should 

 grudge this new view being smothered in your address, and 

 should like to see a separate paper. The one great channel 

 to Santorin and Palma, etc., etc., is just like the one main 

 channel being kept open in atolls and encircling barrier 

 reefs, and on the same principle of water being driven in 

 through several shallow breaches. 



I of course utterly reprobate my wild notion of circular 

 elevation ; it is a satisfaction to me to think that I perceived 

 there was a screw loose in the old view, and, so far, I think 

 I was of some service to you. 



Depend on it, you have for ever smashed, crushed, and 



1 This refers to Banks' Cove : see Volcanic Islands ^ p. 107. 



2 See Lyeli " On Craters of Denudation, with Observations on the 

 Structure and Growth of Volcanic Cones," Quart. Journ. Geol. 



Vol. VI., 1850, p. 207. 



