chap. viii. Elevation of Patagonia. 201 



measured by the Officers of the Survey ; they were all 

 capped by thick beds of gravel, and were all more or 

 less denuded : the 950 plain consists merely of separate, 

 truncated, gravel-capped hills, two of which, by measure- 

 ment, were found to differ only three feet. The 430 

 feet plain extends, apparently with hardly a break, to 

 near the northern entrance of the Rio Santa Cruz (fifty 

 miles to the south) ; but it was there found to be only 

 330 feet in height. 



On the southern side of the mouth of the Santa Cruz 

 we have the following section, which I am able to give 

 with more detail than in the foregoing cases : — 



No. 19. 

 Section of Plains at the mouth of the Rio Santa Cruz. 





840 ft. An. M. 



710 An. M. 



CO . 



pq 



Shells 

 on sur- 

 face. 



.~^' 







V 



«5 . 



DO 



^_ 





rri 









~\ 



Level of sea. Scale -^ of inch to 100 feet vertical. 



The plain marked 355 feet (as ascertained by the 

 barometer and by angular measurement) is a continua- 

 tion of the above-mentioned 330 feet plain : it extends 

 in a NW. direction along the southern shores of the 

 estuary. It is capped by gravel, which in most parts is 

 covered by a thin bed of sandy earth, and is scooped out 

 by many flat-bottomed valleys. It appears to the eye 

 quite level, but in proceeding in a SSW. course, towards 

 an escarpment distant about six miles, and likewise 

 ranging across the country in a NW. line, it was found 

 to rise at first insensibly, and then for the last half mile, 

 sensibly, close up to the base of the escarpment : at 

 this point it was 463 feet in height, showing a rise of 

 108 feet in the six miles. On this 355 to 463 feet 

 plain, I found several shells of Mytilus Magellanicus 



m 



