T96 Elevation of Patagonia. paet n. 



ceed ; but if, as I believe, the upper escarpments once 

 formed the shores of an estuary, in that case the sand- 

 stone formation of the river Negro would have afforded 

 an inexhaustible supply of sand, which would naturally 

 have accumulated on the northern shore, as on every 

 part of the coast open to the south winds between Bahia 

 Blanca and Buenos Ayres. 



At San Bias (40° 40' S.), a little south of the 

 mouth of the Colorado, M. d'Orbigny } found fourteen 

 species of existing shells (six of them identical with 

 those from Bahia Blanca), embedded in their natural 

 positions. From the zone of depth which these shells 

 are known to inhabit, they must have been uplifted 

 thirtv-two feet. He also found, at from fifteen to 

 twenty feet above this bed, the remains of an ancient 

 beach. 



Ten miles southward, but 120 miles to the west, at 

 Port S. Antonio, the Officers employed on the Survey 

 assured me that they saw many old sea-shells strewed 

 on the surface of the ground, similar to those found on 

 other parts of the coast of Patagonia. At San^ Josef, 

 ninety miles south in nearly the same longitude, I found, 

 above the gravel, which caps an old tertiary forma- 

 tion, an irregular bed and hillocks of sand, several feet 

 in thickness, abounding with shells of Patella deaurita, 

 Mytilus Magellanicus, the latter retaining much of its 

 colour ; Fusus Magellanicus, (and a variety of the same) 

 and a large Balanus (probably B. Tulipa), all now found 

 on this coast : I estimated this bed at from eighty to 

 one hundred feet above the level of the sea. To the 

 westward of this bay, there is a plain estimated at be- 

 tween 200 and 300 feet in height : this plain seems, 

 from many measurements, to be a continuation of the 

 sandstone platform of the river Negro. The next 

 1 ' Voyage,' &c. p. 54. 



