754 RALPH ARNOLD AND ROBERT ANDERSON 
DEPTH TO WHICH ALTERATION HAS EXTENDED 
The depth to which alteration has extended below the surface in 
these cases is difficult to determine. A cliff of burnt shale 50 to 100 
feet high is exposed 44 miles due south of Guadalupe, and the differ- 
ence of elevation of points in the Redrock Mountain neighborhood 
where the altered rock outcrops amounts to several hundred feet. 
Fic. 1.—Hand specimen of typical diatomaceous shale from the Santa Maria 
oil district, Santa Barbara County, California (slightly reduced). 
That such metamorphism of the shale has not been solely a surface 
phenomenon is shown by the fact that burnt shale has been found on 
drilling at considerable depths. Mr. Orcutt, of the Union Oil Com- 
pany, exhibited samples of red shale, coming from depths of 950 to 
1,040 feet below the surface in Hill well No. 1 in the Lompoc Field, 
which are identical in appearance and texture with the burnt shale 
elsewhere. Traces of petroleum were associated with the upper 
stratum of burnt shale in this instance. There are numerous wells 
in the Santa Maria field in which red shale, doubtless burnt, was met 
with at depths varying between go feet and 330 feet below the surface. 
The hardening consequent upon the burning has sometimes rendered 
the rock difficult to drill through. 
