1875.] 185 IDenton. 



the same size, taken from a heap of refuse, and noted between them 

 the following differences, which seemed to be pretty constant through- 

 out: the fossil shells are much heavier and thicker, especially near 

 the margin, and at the back ; the concentric sculpture is coarser, 

 broader and more prominent; there is a less perceptible tendency 

 toward the formation of two rounded ridges on the anterior end, 

 passing from the beak toward the ventral region; the hinge-teeth are 

 coarser, and separated by wider intervals; the lateral teeth are much 

 stouter; the muscular impressions deeper; and notwithstanding the 

 greater general coarseness of the shells, the beading along the inner 

 edge of the margin is generally finer. 



A letter was also read from Mr. William Denton, calling 

 attention to an asphalt bed near Los Angeles, California. 



The locality is known as Major Hancock's Brea Ranch, and is 

 about eight miles west of Los Angeles, in the valley of the Santa 

 Anna. The bed of asphaltum here covers sixty to eighty acres, and 

 at a depth of thirty feet no bottom has been reached. Thousands of 

 tons have been removed for roofing, paving and combustion, but the 

 supply is almost inexhaustible. 



Major Hancock had about twenty-five Chinamen employed in dig- 

 ing out the best of the asphaltum, which is soft enough to agglutinate 

 in the heat of the sun. The material was conveyed to large, open 

 iron boilers, in which it was boiled for twenty-four hours, and then 

 run into sand moulds ; subsequently it was broken up, for it is quite 

 brittle after being thus boiled, carted for nine miles and shipped to 

 San Francisco, where it was sold for twenty dollars a ton for making 

 asphalt pavement. The bed is about three miles south of the Santa 

 Monica range of mountains, and it appears to lie parallel with them. 



Beds of petroleum shale of tertiary age, having in many places a 

 thickness of about two thousand feet, are to be found along the Cal- 

 ifornia coast, and at some distance in the interior ; they are said, by 

 Prof. Whitney, to extend from Cape Mendocino to Los Angeles, a 

 distance of about four hundred and fifty miles. They are exposed 

 in cliffs on the coast near Santa Barbara and Carpinteria, and other 

 places. This shale, there is good reason to believe, is the deposit 

 from which all the asphaltum of California has been derived. 



