chap. vin. Area of Recent Elevation. 209 



as the level Pampas ranges many hundred miles north- 

 ward of the point, where M. d'Orbigny found at the 

 height of 100 feet beds of the Azara, the space in a 

 north and south line, which has been uplifted within 

 the recent period, must have been much above the 

 1,180 miles. By the term ' recent,' I refer only to that 

 period within which the now living mollusca were 

 called into existence ; for it will be seen in the eleventh 

 Chapter, that both at Bahia Blanca and P. S. Julian, the 

 mammiferous quadrupeds which co-existed with these 

 shells belong to extinct species. I have said that the 

 upraised shells were found only at intervals on this line 

 of coast, but this in all probability may be attributed 

 to my not having landed at the intermediate points ; 

 for wherever I did land, with the exception of the 

 river Negro, shells were found : moreover, the shells 

 are strewed on plains or terraces, which, as we shall 

 immediately see, extend for great distances with a 

 uniform height. I ascended the higher plains only in 

 a few places, owing to the distance at which their 

 escarpments generally range from the coast, so that I 

 am far from knowing that 410 feet is the maximum of 

 elevation of these upraised remains. The shells are 

 those now most abundant in a living state in the 

 adjoining sea. 1 All of them have an ancient appear- 

 ance ; but some, especially the mussels, although lying 

 fully exposed to the weather, retain to a considerable 

 extent their colours : this circumstance appears at first 

 surprising, but it is now known that the colouring 

 principle of the Mytilus is so enduring, that it is pre- 

 served when the shell itself is completely disintegrated. 2 



1 Capt. King, ' Voyages of Adventure and Beagle,' vol. i. pp. 6 

 and 133. 



2 See Mr. Ly ell's ' Proofs of a Gradual Eising in Sweden,' in the 

 « Philosoph. Transact.' 1835, p. 1. See also Mr. Smith, of Jordan 

 Hill, in the ' Edin. New Phil. Journal,' vol. sxv. p. 393. 



