METAMORPHISM IN OIL-BEARING SHALE 751 
typical occurrences of shale altered in this way in the region of the 
oil fields of Santa Barbara County. 
The Monterey shale, of middle Miocene age, is the oil-bearing 
formation, and the process of burning has had its chief effect upon 
portions of this formation. It is composed almost exclusively of soft 
and hard, thin-bedded, siliceous shales, which are largely of diatoma- 
ceous origin (see Fig. r). 
INSTANCES IN WHICH THE SHALE IS AT PRESENT BURNING 
A number of instances have been observed in which combustion 
is at present or has been in recent years in progress within the Mon- 
terey shale. One example is afforded on the north side of Graciosa 
Ridge south of the Santa Maria Valley near the Rice Ranch oil well 
No. 1.. When this locality was visited by the writers early in the 
autumn of 1906 a fire was burning underground in the shale, causing 
a smoke of disagreeable odor to issue from the surface and making 
the ground hot over an area of many square yards. Oil was oozing 
up at various points near by, and the ground was heated in the 
neighborhood of all of these seepages. The holes from which vapor 
issued were coated with delicate crystals of sulphur. At the point 
where the burning was actually going on and all about in the vicinity, 
for a distance of several hundred feet in some directions, the shale 
was altered to a bright red color, or baked almost to the hardness of 
compact igneous rocks, or rendered vesicular like lava. 
There can be no doubt that this fire was supported by the bitu- 
minous material in the shale, and its starting was probably due to 
brush fires. The brush round about had been burnt, but the fire had 
swept over it a good many months before, as shown by the new growth 
on the bushes. It was said that there was a brush fire about January 
1, 1906, which started the fire in the shale, and that futile attempts 
had been made ever since that time to put out the underground fire 
by dumping dirt upon it in the attempt to smother it. It seems 
likely, however, that this same fire has been in progress for several 
years. This likelihood is borne out by other accounts. It is stated 
that sometimes during the course of brush fires on the hills sudden 
darts of flame may be seen at night from a considerable distance— 
the result of the setting on fire of gas escaping from the rocks. 
