30 E. T. DUMBLE 
name of Oil Canyon. A few years ago, two or three wells were sunk 
here in a search for oil, but failed to develop it. The north bank 
of this canyon gives us very distinctly the relations of the Cretaceous 
and Eocene. 
The Chico is represented through the greater part of its exposure 
by a purple shale identical in appearance with that of the Coalinga 
region. Through a part of this shale there are beds of concretionary 
clayey limestone with ammonites and other Chico forms. Above 
this, the concretions, scattered irregularly through the shale, take 
the form of a very fine-grained blue limestone which weathers 
perfectly white. Toward the eastern end of the exposure this 
purple shale is overlain by a gray sandstone weathering brown. It 
is rather coarse grained as a whole, even conglomeratic in places, 
and is quite massive in structure. It carries limy concretions which 
contain fragments of Inocerami. 
The lowest Eocene or Martinez deposit begins with a brown 
sand and sandy shale, more or less glauconitic, with limy concre- 
tions carrying a Martinez fauna. Higher in the section the shaly 
nature of the beds becomes more pronounced and they carry con-- 
cretionary nodules of limestone and ironstone. Near the center 
of the section, as exposed here, there is a band of coarse red sand- 
stone with some greensand, green mica, and casts of fossils. It is 
only a few feet in thickness and is succeeded by brown shales which 
carry more and more clay toward the top and more numerous and 
larger concretions of clay-ironstone, and lime. 
At the west end of this section, opposite the head of Oil Canyon, 
the Martinez sandy shales rest on the Chico purple shale imme- 
diately above the band of the clayey limestone with ammonites. 
Going eastward a mile, higher and higher beds of the Chico shale 
appear under the Martinez until, at a horizon fully 125 feet strati- 
graphically above the first observed contact, the point of the sand- 
stone wedge comes in and thickens until there is a body of at least 
80 feet of it exposed below the Martinez. 
While the exact point of contact is difficult to place where the 
two shale beds come together, it is entirely possible to say within 
a few feet of such contact, ‘‘ This is Chico,” or ‘‘This is Martinez,” 
from their dissimilarity. On the sandstone, however, the contact 
