to Professor Henslow of Cambridge. 443 



Since leaving the Rio Plata, I have had some opportunities of examining 

 the great southern Patagonian formation. I have a good many shells : 

 from the little I know of the subject, it must be a tertiary formation ; for 

 some of the shells (and corallines) now exist in the sea. Others, I believe, 

 do not. This bed, which is chiefly characterised by a great oyster, is 

 covered by a very curious bed of porphyry pebbles, which I have traced for 

 more than 700 miles. But the most curious fact is, that the whole of the 

 east coast of the southern part of South America has been elevated from 

 the ocean since a period during which muscles have not lost their blue 

 colour. At Port St. Julian I found some very perfect bones of some large 

 animal, I fancy a Mastodon : the bones of one hind extremity are very per- 

 fect and solid. This is interesting, as the latitude is between 49° and 50°, 

 and the site far removed from the great Pampas, where bones of the nar- 

 row-toothed Mastodon are so frequently found. By the way, this Mastodon, 

 and the Megatherium, I have no doubt, were fellow brethren in the ancient 

 plains. Relics of the Megatherium I have found at a distance of nearly 

 600 miles in a north and south line." 



Corallines, Propagation of. — "I have already seen enough to be con- 

 vinced that the present families of corallines, as arranged by Lamarck, 

 Cuvier, &c, are highly artificial. It appears to me, that they are in the 

 same state in which shells were when Linnaeus left them for Cuvier to re- 

 arrange I forget whether I mentioned having seen something of the 



manner of propagation in that most ambiguous family, the corallines : I feel 

 pretty well convinced that, if they are not plants, they are not zoophytes : 

 the " gemmule " of a Halimeda contains several articulations united, ready 

 to burst their envelope, and become attached to some basis. I believe that 

 in zoophytes, universally, the gemmule produces a single polypus, which 

 afterwards, or at the same time, grows with its cell, or single articulation." 



Geology of the Andes. — " Shortly after arriving here, I set out on a geo- 

 logical 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 often completely altered, 

 by the action of fire. The varieties of porphyry thus produced are endless ; 

 but no where have I yet met with rocks which have flowed in a stream. 

 Dykes of greenstone are very numerous. Modern volcanic action is en- 

 tirely shut up in the very central parts (which cannot now be reached, on 

 account of the snow) of the Cordilleras. To the south of the Rio Maypo, I 

 examined the tertiary plains, already partially described by M. Gay. The fossil 

 shells appear to me to differ more widely from the recent ones than in the 



great Patagonian formation I have been much interested by finding 



abundance of recent shells at an elevation of 1300 ft. * The country iu many 

 places, is scattered over with shells ; but these are all littoral ones ! So that 

 I suppose the 1300 ft. elevation must be owing to a succession of small ele- 

 vations, 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 run- 

 ning water, or the sea, formed this ravine ? was a question which often arose 

 in my mind, and was generally answered by my finding a bed of recent 

 shells at the bottom. I have not sufficient arguments ; but I do not believe 

 that more than a small fraction of the height of the Andes has been formed 

 within the tertiary period." 



Earthquake. — " Valparaiso. You will have heard an account of the 

 dreadful earthquake of the 20th of February. I wish some of the geologists 

 who think the earthquakes of these times are trifling could see the way in 



* Though these shells may be similar to recent ones, we have no proof 

 that the species have not existed in the southern hemisphere, in very an- 

 cient epochs. — B. k k 2 



