18 EARLY LETTERS [Chap. I 



Letter 5 Natural History, and a son may talk about himself to his 

 father. In your paternal capacity as proproctor what a 

 great deal of trouble you appear to have had. How turbulent 

 Cambridge is become. Before this time it will have regained 

 its tranquillity. I have a most schoolboy-like wish to be 

 there, enjoying my holidays. It is a most comfortable reflec- 

 tion to mc, that a ship being made of wood and iron, cannot 

 last for ever, and therefore this voyage must have an end. 



October 28th. This letter has been lying in my port- 

 folio ever since July ; I did not send it away because I 

 did not think it worth the postage ; it shall now go with 

 a box of specimens. Shortly after arriving here I set out 

 on a geological excursion, and had a very pleasant ramble 

 about the base of the Andes. The whole country appears 

 composed of breccias (and I imagine slates) which universally 

 have been modified and oftentimes completely altered by the 

 action of fire. The varieties of porphyry thus produced are 

 endless, but nowhere have I yet met with rocks which have 

 flowed in a stream ; dykes of greenstone are very numerous. 

 Modern volcanic action is entirely shut up in the very 

 central parts (which cannot now be reached on account of 

 the snow) of the Cordilleras. In the south of the R. Maypu 

 I examined the Tertiary plains, already partially described 

 by M. Gay. 1 The fossil shells appear to me to be far more 

 different from the recent ones than in the great Patagonian 

 formation ; it will be curious if an Eocene and Miocene 

 (recent there is abundance of) could be proved to exist 

 in S. America as well as in Europe. I have been much 

 interested by finding abundance of recent shells at an eleva- 

 tion of 1,300 feet ; the country in many places is scattered 

 over with shells but these are all littoral ones. So that I 

 suppose the 1,300 feet elevation must be owing to a succession 

 of small elevations such as in 1822. With these certain 

 proofs of the recent residence of the ocean over all the lower 

 parts of Chili, the outline of every view and the form of each 

 valley possesses a high interest. Has the action of running 

 water or the sea formed this deep ravine? was a question 

 which often arose in my mind and generally was answered 



1 " Rapport fait a PAcademie Royale des Sciences, sur les Travaux 

 G^ologiques de M. Cay," by Alex. Brongniart (Ann. Sri. Nat., Vol. 

 XXVIII., p. 394, 1833). 



