GEOLOGY. 
37 
resemble shale in its thin stratification, the great difference being in 
the siliceous instead of argillaceous composition. Locally there are 
beds of clayey nature in the upper division which form a connecting 
link between the ‘ ‘ chalk rock/ ’ as the diatomaceous shale is colloquially 
termed, and common clay shale. Characteristic oval and lenticular 
yellow concretions of hard lime are commonly included in the shale 
of the upper division. They range in diameter from a few inches to 2 
feet or more. In many places they occur at irregular intervals and 
of irregular size along a bedding plane, locally displacing the ordinary 
shale and interrupting the continuity of not merely one bed but many 
thin beds. They are invariably elongated parallel with the bedding. 
Volcanic ash is interbedded with the soft shale of the upper divi¬ 
sion in the hills immediately south of Lompoc. It is very fine grained, 
soft, and uncompacted, and probably corresponds in composition to 
rhyolite. It somewhat resembles the pulverulent diatomaceous earth, 
but is easily distinguishable by its grayish color and grittiness. 
The upper portion of the Monterey, like the lower, is to a large 
extent impregnated with bituminous material. It is apt almost 
anywhere in this region to give out a bituminous odor when broken 
into or to show a brownish discoloration due to the presence of oil. 
In places the shale, otherwise white, is specked with minute black 
spots of bitumen. Thin sandy layers occur sparingly interbedded 
with the shale, and these almost without exception have absorbed 
considerable oil and have a dark-brown color and strong odor. But 
these beds of sand are very rare and make up no appreciable propor¬ 
tion of the series. 
The soft varieties of the Monterey shale are almost invariably 
alkaline and have a salty taste. They contain an abundance of 
salts easily soluble in water that form characteristic wooly coatings 
of efflorescence on the surface of outcrops. This is especially true 
near the summit of the formation, where a soft claylike gypsum¬ 
bearing shale locally marks the contact with the Fernando above. 
This gypsum is crystallized in plates along seams and bedding planes 
much like the gypsiferous clay of the Casmalia Hills, which is sup¬ 
posed to be Vaqueros in age. Zones of gypsiferous shale occur also 
at other places in the upper division of the Monterey, but it is not 
known whether there are any single horizons at which it is constant. 
Where the gypsum occurs the shale is usually of more argillaceous 
character and bears a closer resemblance to ordinary clay shales. 
The significance of this alkalinity in the Monterey is unknown. 
The organic shale is considered to be of marine origin in fairly deep 
water, and owing to the almost complete absence of all but the 
finest grained detritus the alkalinity can not be considered as proof 
of shallow-water or brackish-water origin. The salts may have 
some relation to the chemical changes involved in the production of 
petroleum. 
