2 1 6 Elevation Gradual. part n. 



their preservation. I saw a multitude of spots in Bahia 

 Blanca where this might have been effected; and at 

 Maldonado it almost certainly has been effected. In 

 speaking of the elevation of the land having been slow, 

 I do not wish to exclude the small starts which accom- 

 pany earthquakes, as on the coast of Chile ; and by such 

 movements beds of shells might easily be uplifted, even 

 in positions exposed to a heavy surf, without undergoing 

 any attrition : for instance, in 1835, a rocky flat off the 

 island of Santa Maria was at one blow upheaved above 

 high-water mark, and was left covered with gaping and 

 putrefying mussel-shells, still attached to the bed on 

 which they had lived. If M. d'Orbigny had been aware 

 of the many long parallel lines of sand-hillocks, with 

 infinitely numerous shells of the Mactra and Venus, at 

 a low level near the Uruguay ; if he had seen at Bahia 

 Blanca the immense sand-dunes, with water- worn pebbles 

 of pumice, ranging, in parallel lines, one behind the other 

 up a height of at least 120 feet ; if he had seen the sand- 

 dunes, with the countless Paludestrinas, on the low plain 

 near the Fort at this place, and that long line on the edge 

 of the cliff, sixty feet higher up ; if he had crossed that 

 long and great belt of parallel sand-dunes, eight miles in 

 width, standing at the height of from forty to fifty feet 

 above the Colorado, where sand could not now collect, — 

 I cannot believe he would have thought that the eleva- 

 tion of this great district had been sudden. Certainly the 

 sand-dunes (especially when abounding with shells), 

 which stand in ranges at so many different levels, must 

 all have required long time for their accumulation ; and 

 hence I do not doubt that the last 100 feet of elevation 

 of La Plata and Northern Patagonia has been exceed- 

 ingly slow. 



If we extend this conclusion to Central and Southern 

 Patagonia, the inclination of the successively rising 



