WEST COAST PULMONATA. 507 



tertiary east slope south of the great rivers. I did not 

 reach that region on the geological survey, but Dr. Yates 

 found there Nos. 11, 25, 36, 37 in considerable numbers, 

 and No. 37 also along the. outlet of Clear Lake near 

 lat. 39°, where it cuts through the same fossiliferous strata, 

 although not existing around the lake itself. Here we have 

 almost certain proof that No. 37 is not a variety of 36, both 

 living together unchanged. Fig. 2224 is the highest point 

 on the southeast boundary, at the angle west of the figures. 



Solano County. 



A volcanic ridge runs north, from west of Suisun Creek 

 into Napa County, but the rest of Solano is of cretaceous 

 and tertiary strata containing fossils, excepting the plain 

 sloping eastward from about two hundred feet elevation to 

 the marshes, where only Limacoid and Succinoid species 

 are known to exist. 



Mare Island, of pliocene formation, containing bones of 

 land quadrupeds, is the most northern and western known 

 locality of No. 32. No. 25 occurs near there, and Nos. 44 

 and 45 are to be looked for as in Contra Costa near the 

 marshes, from Suisiin Creek eastward. No. 14, first found 

 in Trinity County, must be expected there, also some of the 

 northern forms that occur Avestward. Small varieties of 

 Nos. 26 and 30 have been found near the borders of Napa 

 County, as in Contra Costa County, but not along any 

 streams of the Sacramento basin. 



GEOLOGICAL AND BIOLOGICAL DEDUCTIONS. 



I. The marine pliocene fossils found along Mark West 

 Creek, Sonoma County, in San Mateo County, Pajaro Val- 

 ley, and northeast of Mount Diablo, now elevated at all 

 these points about 300 feet above the sea, show that Marin 

 County, San Francisco County, and the Santa Cruz Moun- 

 tains, once formed islands 300 feet or more lower in the 



