36 SANTA MARIA OTL DISTRICT, CALIFORNIA. 
UPPER DIVISION. 
The line of division between the lower and upper portions of the 
Monterey is rather arbitrary, yet if each portion is taken as a whole 
the lithologic distinction is marked, and the separation is made natural 
by the areal limitations of the outcrops of one or the other in various 
places. Where they are in contact a conformity between the two 
halves of the formation is evident and a gradation occurs from the 
porcelaneous and flinty shales of the lower part into the light-colored, 
earthy beds of the upper. Such is the occurrence, for instance, near 
the north edo-e of the hills 4 miles west-southwest of the town of 
Lompoc. 
The greater part of the upper division is made up of white or light 
chocolate-colored diatomaceous shale, usually of light weight and 
porous, but grading in places into heavier and harder, more compact, 
brittle, porcelain-like shale. The soft shale is extremely fine grained, 
rarely being at all gritty. The bedding is characteristically very thin, 
but where great masses of the soft white shale, which goes by the 
name of diatomaceous earth, occur, lines of bedding are usually 
indistinguishable, except here and there on thin projecting laminae 
produced by weathering, or on the upper surface of small cavities 
due to the eating out of less resistant patches. PI. IV illustrates two 
characteristic types of the soft unaltered shale. In the upper view 
it is massive, and bedding planes are almost indistinguishable except 
for lines brought into relief by weathering and erosion. In the lower 
view it is slightly more compact and lies in distinct platy layers. 
Major bedding planes from a fraction of an inch to several inches 
apart are distinctly apparent, and there is a further laminated struc¬ 
ture that enables the shale to be split into plates of extreme thinness. 
An artificial cut through somewhat disintegrated shale of the upper 
part of the Monterey is shown in PI. VIII, A (p. 78). The typical 
unaltered diatomaceous shale is pictured in PI. V, A. The small 
round diatom tests of which it is largely composed are faintly distin¬ 
guishable with the naked eye in the photograph. In general, both 
the softer and harder varieties of the Monterey shale, owing to their 
siliceous composition, do not give way readily to decomposition or 
weathering. Local chalcedonic lenses are to be found in this series 
roughly following the bedding planes in unaltered shale, as well as 
horizons of hard, porcelaneous, usually much-fractured shale; but 
the latter does not become predominant over the softer shale as it 
does in the lower division. 
The white chalklike deposits of this formation are not fully described 
by the use of the word shale in its ordinary sense. Especially in the 
massive deposits, where bedding is not very apparent, it has neither 
in composition nor lamination the character of ordinary shale. But 
this word has come into use in connection with the Monterey for lack 
of any other. The major portion of the formation, however, does 
