132 CALIFORNIA ACADEMY OF SCIENCES. 



made it 276 feet higher, and he thinks some peaks are- 

 over 7,000 feet. 



None of these figures indicate the highest points of the 

 peaks, only the camps. 



The preceding are all along the central ridge of the 

 peninsula, and the Coast Survey gives heights of two 

 somewhat parallel ridges varying from 773 feet near Todos 

 Santos Creek to 2,183 *o^* ^^e western, and 443 near 

 Punta Arena to 4,419 further south on the eastern side of 

 the peninsula. 



This mountainous region extends about as far north as 

 south of the tropic, which thus crosses the center of it. 

 There the level suddenly falls to a low plain from 75 to 

 100 feet above the sea, extending clear across the penin- 

 sula, so that there is little doubt of the former existence 

 of the southern region as a tropical island, about 100 

 miles long and 40 miles wide. From this isolation many 

 peculiarities of the molluscan life may be expected, a& 

 compared with the more northern regions. 



Sierra Laguna is named from the former existence of a 

 lagoon somewhere on it, which is reported to have bro- 

 ken away its boundaries and become dry. There is not 

 believed to be any fresh-water lagoon anywhere on this 

 mountainous region south of La Paz, but some brackish 

 ones exist at the mouths of creeks in the dry season. 



The onl}^ fresh-water shells found higher than Santa 

 Anita were the Limnophysa, Physa and Pisidium, named 

 in these Proceedings, 2d series, vol. iii, p. 217, which 

 live near the springs that do not entirely dry up. The 

 Pisidium may often be found where only dampness re- 

 mains, and can crawl up the streams in that condition, 

 or, if still drier, buries itself in the mud, perhaps for 

 years, to await the next shower. 



