WEST COAST PULMONATA. 371 



32, 36, 42, 43, four of which were found also on the eastern 

 border. 



The western slope of the mountains forming the eastern 

 shore of the bay (called Contra Costa hills), is mostly of 

 metamorphic rocks near its base, but partly covered with 

 pliocene gravels up to 300 feet, while miocene sandstone 

 with many fossils forms the summits and eastern slopes of 

 tlie spur. The creeks draining it all head within this fos- 

 siliferous region, and carry down lime in abundance to 

 the valley soils. There are also calcareous springs deposit* 

 ing tufa along the junction of the pliocene and metamorphic 

 rocks in many places. It receives the full effect of the sum- 

 mer fogs condensing about the summits, as well as more 

 winter rain tlian eastward, while the sea breezes keep it 

 cool in summer. We therefore find it the most favorable^ 

 region yet mentioned for land pulmonates, which, however^ 

 still seem absent everywhere above 1,000 feet elevation. 



The influence of these new conditions is seen here also 

 in the commencement of a new group of botanical sj^ecies,^ 

 accompanied to some extent by animals also, of species not 

 known east oi- southward in the Mt. Diablo range, but char- 

 acterizing the coast ranges west and north of San Francisco 

 Bay. The most conspicuous example of this is the isolated 

 grove on Kedwood Peak; but some of the shrubs and 

 smaller plants have a wider range. 



Although Rocky Mound, five miles north, is much 

 higher, its upper parts are entirely metamorphic, and thus 

 unsuited for the redwood. The Peak has its eastern slope 

 and summit composed of sandstone lying upon serpentine,. 

 and at the junction numerous springs come out forming, 

 creeks running in every direction. 



The redwood trees grew^ in 1850 pretty thickly over a sur- 

 face about two miles square at the summit, mostly in clumps 

 around the springs, and becoming scarcer down to about 500 

 feet elevation. Though many hills in the ridge are as higk 

 or higher, this was the only one so wooded, being the 



