572 H. W. FAIRBANKS 
One of the most striking structural features is the occurrence 
in the Monterey shales of the Buchon range of great bodies of 
bituminized sand forced into its present position during the 
folding which terminated the deposition of the San Pablo forma- 
tion. There are two of these sand pockets or bosses north of 
Sycamore Springs. They occur near the ends of subordinate 
anticlinal folds. The largest body of sand is fully 500 feet 
across, elongated somewhat in the direction of the strike of the 
shales and with narrow dikes radiating from it. The sand has 
probably been forced in from beneath from the adjoining San 
Pablo formation, as the nose-shaped terminations of the anti- 
clines in which the sand appears have been forced slightly over 
that formation. 
The structural relations of some of the igneous rocks are 
quite remarkable. Especially is this true of those which have 
appeared in the Monterey series. Bodies of the teschenite and 
olivine diabase magmas have come up underneath this series 
but have rarely if ever broken completely through it. Having 
penetrated as far upward as the limestones or bituminous shales 
they have spread out between the strata in sheet form. Two 
remarkable cases occur north of San Luis Obispo between it and 
the railroad water tanks. Here are two hills, one a half mile 
in diameter, the other nearly a mile, rising quite abruptly from 
the lower rolling country and capped by a thin layer of Mon- 
terey limestone and shale. Each hill has an amphitheater-like 
center, the strata dipping inward from all sides but one, and from 
this a depression has been eroded. The peculiar topography 
and saucer-like structure is due in each case to a sheet of tes- 
chenite which outcrops around the steep outer slope metamor- 
phosing the overlying rocks. From a general study of the 
region it seems likely that the Monterey series had already 
undergone disturbance and folding when these igneous rocks 
appeared. 
One of the crests of the Santa Lucia range about 20 miles 
north of San Luis Obispo has on its summit a long narrow rem- 
nant of Monterey shales folded in synclinal form. For some 
