606 CALIFORNIA ACADEMY OF SCIENCES. 



there are many old craters on this ridge, the first one met 

 with being Mount St. Helena, of which the summit is nine 

 miles north of the map, on the north boundary of Napa 

 County. There are, however, numerous sulphur and hot 

 springs, which show that the volcanic forces h ive not yet 

 died out, and the region covered more or less by volcanic 

 materials extends entirely across the ridge west of Napa 

 Creek, and over most of that east of it, as far at least as the 

 heads of streams running into the Sacramento basin. We 

 thus have a region about twenty-five miles wide of volcanic 

 materials, alternating with tertiary deposits containing 

 fossil wood, lignite and other terrestrial products, but no 

 fossil shells yet known. Lime is therefore scarce, and the 

 still heated mineral waters show that during the deposition 

 of these strata animal or vegetable life must have been 

 interrupted as far as the volcanic influence extended, either 

 by flows of lava, hot water or ashes, until the quaternary 

 epoch. 



I explored Sonoma Mountain, the head of Napa Yalley, 

 and the whole shore of Clear Lake , finding very few land 

 pulmonates, though six aquatic forms inhabit the lake, 

 as well as six non-pulmonate mollusca, while some are also 

 found in several of the creeks of the region, but much fewer 

 than we might expect. This may be considered further 

 proof that these streams have been not long ago heated or 

 mineralized enough to destroy mollusca. Of land species, 

 I can only mention Nos. 1, 4 (or 5), 9 (or 10), 43, 45, as 

 certainly found in the volcanic region, most of which re- 

 quire scarcely any lime, and the two last are almost aquatic. 



East of this region we find the foothills forming the east 

 slope of the Coast range, about the headwaters of Putah 

 Creek, composed of cretaceous and tertiary rocks contain- 

 ing fossils, and iiere are again found, forty-five miles inland, 

 some of the land shells of tlie west slope, which, with the ex- 

 tensive and luxuriant forest covering much of the country, 

 indicates that the climate is much less arid than along the 



