508 CALIFORNIA ACADEMY OF SCIENCES. 



ocean than now, and the Mount Diablo range, if not an 

 archipelago, was nearly surrounded by water. In this, great 

 beds of pliocene gravels, containing remains of land an- 

 imals, Avere deposited by the streams running from the 

 Mount Hamilton range, while Livermore Valley probably 

 contained a large lake, discharging tlirough Walnut Creek, 

 before the present Alameda Creek cut through the western 

 hills. Fossil fresh water shells found along branches of 

 Walnut Creek both east and west, near Mission Peak, etc., 

 show that lakes or marshes were extensive in pliocene and 

 quaternary times. 



II. No extinct land -pulmonata have been found with 

 these fresh water forms (of which several are extinct), but 

 in hit n- beds on Walnut Creek, containing living fresh water 

 forms, are two living land species, Nos. 32 and 33, showing 

 that they were the first of the group to appear in the center 

 of the range they now inhabit east of the Bay. These fossils 

 are plainly quaternary, and the living shells of these two 

 forms become more or less graded into 30, 31, 35, etc., 

 toward the west and south, indicating probably that they 

 may have been the original stock from which the latter were 

 derived. From Marin County a specimen of No. 35 (?) has 

 been brought in a fossil state, unlike those now living 

 southward, being the only evidence known of any fossil 

 forms north of the bay. 



III. These few evidences show that the forms of the 

 most characteristic group occurring in the bay region, the 

 Ariontce, are either indigenous, or derived from the coast 

 range northward, and have colonized the region during the 

 quaternary epoch, no preceding extinct forms having been 

 discovered there, and no evidence of a transition direct 

 from the Sierra Nevada. 



IV. The species given in the table as found also in the 

 Sierras, are, 1st, Limacoid, and therefore easily carried by 

 floods without injury; 2d, Vitrinoid, mostly very small, and 



