AUSTRAL-AMERICAN REGIONS. 71 



CHAPTER V. 



AUSTRAL-AMERICAN REGIONS. 



Leaving Brazil on the 7th of January, 1839, the Vincennes and 

 other vessels of the squadron proceeded South ; and on the 25th, 

 anchored at the mouth of the Rio Negro, at the Northern extreme 

 of Patagonia. 



1. Patagonia. 



Our Latitude was now about 41° South, and the change in the 

 character of the country could not be more complete. Before us, was 

 only a continuous low line of land, devoid of trees, arid and brown. 

 By closer inspection, undulating sand-hillocks were distinguished ; ex- 

 tending as far as three miles south of the river-mouth, where a well- 

 defined bluff comes out to the sea. 



Afterwards, on landing, this bluff, about a hundred feet high, was 

 found to mark the real elevation of the whole country: for we looked 

 out upon a naked, endless plain, where the sun goes down as it does 

 upon the ocean, intercepting in the distance only some very slightly- 

 swelling variations of level. The sand-hillocks in front of our anchor- 

 age, were now perceived to occupy a wide river-trench ; formed by the 

 vast body of flowing water in wearing a passage through this upland 

 plain. 



The geological structure was in various places manifest ; a tertiary 

 sand-rock, horizontally stratified, usually crumbling between the fingers, 

 but in some layers seeming sufficiently indurated for building purposes. 

 Mr. Dana remarked " a considerable mixture of lime in the upper 

 stratum ;" and was informed, that " lime is procured by burning." 

 The included fossils were all found to belong to the most recent geo- 

 logical Period. 



The river-brink at first appeared gravelly, but was found to consist 



