6 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
their structure. The shales are of a slightly bluish hue, but discolor 
a rusty brown from the presence of iron or petroleum, or both. The 
mottlings of the quartzites, which are very characteristic, are usually 
about one-fourth inch in diameter, round or irregular in outline, and 
in many instances are as conspicuous as the greener, more homogene¬ 
ous portion of the rock. The sandstones of the formation are usually 
light gray to white, and are only a little less hard and close textured 
than the quartzites. They carry numbers of Ostrea, the shells of 
which are usually black and 4 or 5 inches long by 3 or 4 inches across. 
It is difficult to obtain good specimens of these fossils, and their deter¬ 
minative value remains for the present unknown. 
The quartzites and sandstones greatly predominate in the lower 
2,000 feet of the formation as exposed, and the shales in the upper 
portion, but both types of rock intermingle to a considerable degree, 
imparting thus to the series as a whole a marked uniformity of appear¬ 
ance, which, with the persistency of its principal characteristics, is of 
especial value in identification. The formation contains toward the 
middle quartzites similar to those lower down. 
The conspicuous features of this formation are a tendency to a broad 
concretionary structure in some of its members; the presence of 
smaller brown ferruginous sand concretions; the sparse distribution 
of fossil oysters and other very imperfect molluscan remains through 
a great portion of its thickness, more particularly in the shales; 
some evidences of woody tissue, and a frequent recurrence of what 
appear to be fucoids. 
The upper part of the Topatopa formation on the lower slopes of 
the mountains on the north of the Ojai Valley consists of a succes¬ 
sion of very ferruginous rusty-brown and gray sandstone and sandy 
shale, perhaps 2,500 feet thick in all. This facies of the Topatopa 
extends eastward as far as the Silver Thread field, adjoining the 
Ojai Valley on the east. The dip of the rusty beds at the mouth of 
Senor Canyon is southward, changing to northward at a point 
immediately within the low outer hills of the range. West of the 
canyon the northerly dip is maintained to a point far up the slopes. 
East of the canyon there are a number of flexures of greater or less 
severity, but of short extent. The strata are also bent at this point, 
the strike, which east of Sulphur Canyon is N. 60° to 70° W., west of 
the gorge becomes east and west, or even a little south of west, this 
direction being maintained to a point beyond Matilija Creek. 
Cross-bedding is here and there observable. In the shaly zones there 
is a remarkable tendency to rapid variation in the thickness of the 
component layers; there also appears to be a certain amount of intra- 
formational unconformity. 
