WEST COAST PULMONATA. 503 



large tracts in parks, etc., well watered, and protected from 

 other animals, may favor the increase of some or all of the 

 species in this and other counties. I have known of Nos. 

 1, 3, 5, 16, 17, 21, 26, 30 and its varieties to be found in 

 gardens, while 3 and 16 are imported species, always 

 increasing with cultivation. East of the bay, Nos. 2, 20 

 and 21 have also been found in gardens. 



Marin County. 



This county, though lying partly west of the waters con- 

 nected with San Francisco Bay, and only separated from 

 the last by a narrow channel, differs so much that it is bet- 

 ter grouped with those northward. Before visiting that 

 region, I supposed that the mountains so prominent in that 

 direction must be far better suited to produce land-j)ulmo- 

 nates than the low sandy peninsula, or the drier and less 

 wooded hills southward. 



But while exploring Marin County very carefully, I found 

 none at all on the east slope except near the base of Mount 

 Tamalpais, on Angel Island, wliere a few only exist, 

 and close to the marshy shores of San Pablo Bay, about 

 Indian mounds or in thickets. Those known there, all quite 

 scarce, are Nos. 1, 4 or 5, 6, 9 or 10, 11 or 12, 23, 30, 31, 

 42, 43. Connected with this scarcity, we find a new influ- 

 ence beginning to appear, in the occurrence along the north- 

 east slojDe of the county, of volcanic rocks, as will be later 

 mentioned more fully. 



Most of this eastern slope consists of metamorphic rocks^ 

 thinly covered, and with little lime, while trees and shrub- 

 bery are found only in canons or on rocky ridges. A few 

 redwoods grow at the east base of Mount Tamalpais, while 

 other coniferous trees occur about the summit, and more 

 abundantly toward the north and west, where they give dense^ 

 damp shelter in some localities. Between Mount Tamal- 

 pais and Bolinas Bay the tertiary fossiliferous strata cover 

 the west slope, and there are found Nos. 11, 25, 26, 36, be- 



