758 RALPH ARNOLD AND ROBERT ANDERSON 
colors, such as bright red, rose, brown, yellow, and cream color and it appears 
to have been partially fused in some places. * 
And again he remarks, referring to the same region. 
In some localities the rock has evidently been on fire, and the bituminous 
matter having been burned out—the operation continuing for several years, as 
it is said—the slates are left of various shades of red, produced by the oxidation 
of the iron.’ 
Burnt-shale areas occur in many places besides in Santa Barbara 
County. Mr. G. H. Eldridge? makes the following comment on its 
occurrence and origin in Ventura County where especially good 
examples are to be found south of the valley of the Santa Clara River 
on Oak Ridge and the crest of South Mountain. 
The siliceous shale and ‘‘chalk rock”? forming the crest of the mountains 
south of the Santa Clara have at many points been burned to a bright red color. 
The fuel which supported such fires was perhaps the originally contained petroleum. 
Opposed to this view, however, is the very considerable depth to which the 
shale has been altered to a brilliant red lava-like rock; hence it may be inferred 
that spontaneous combustion alone has brought about the modification. 
RANGE IN TIME OF THE PHENOMENON 
As already mentioned, the marked influence of the hardened shale 
on the topography in certain instances points to its origin in those 
cases a long time since. The age of some of the burnt shale areas is 
further shown by the presence of numerous fragments of it at a depth 
of at least ten feet below the surface in horizontal beds of Pleistocene 
age. These beds are of sand, clay, and rough gravel, and form the 
low hills between Guadalupe Lake and the high hills to the west. 
The fragments of shale are little worn and evidently of local deriva- 
tion; having very possibly come from the cliffs before mentioned south 
of Guadalupe. The fact that the Monterey shale underwent this 
kind of baking in Pleistocene times indicates further that the accumu- 
lation of the oil and its dissemination in the surface rocks took place, 
or was taking place, before the latest orogenic movements in this 
coastal region. 
t “Geol. Survey of California,” 1865, Geology, Vol. I, p. 126. 
2 Ibid., p. 131. 
3 G. H. Eldridge and Ralph Arnold, “The Santa Clara Valley, Puente Hills and 
Los Angeles Oil Districts,” Bull. 309, U. S. Geol. Survey, p. 22, 1907. 
