44 
SANTA MARIA OIL DISTRICT, CALIFORNIA. 
incipient crystallization, are included in the clear bands, giving a brec- 
ciated appearance. The bands are parallel with the bedding planes. 
They are commonly followed and more rarely crossed by veins of 
quartz crystals. 
The limestone is made up of granules of crystalline calcite, or cal- 
cite showing the beginnings of crystallization. Included in this 
extremely fine grained, uniform groundmass are larger but yet very 
small, irregular grains of crystalline calcite, and in places long spicules 
of the same. In some specimens the granules are more minute than 
in others and the included larger grains are fewer. In still others, 
crystallization has entirely altered portions into patches of large, 
intergrown crystals, leaving angular, unchanged patches sharply 
marked off, and thus giving an appearance like that of a breccia. 
The flinty calcareous shale has a minute granular texture, quartz 
grains both crystalline and semicrystalline being associated with those 
of calcite. The rock usually has light and dark bands parallel with 
the bedding, the light bands containing more quartz and having the 
calcite granules less close together than the darker bands. 
CHEMICAL COMPOSITION. 
The subjoined table comprises analyses of different specimens and 
varieties of Monterey shale from the Santa Maria district, with one 
(No. 5) here included for comparison, of a sample of white bitumin¬ 
ous shale from the type locality of the formation at Monterey, farther 
north on the California coast. 
The first three represent typical examples of the unaltered diato- 
maceous shale of the Monterey. Nos. 3 and 2, respectively, are analy¬ 
ses of the same samples that were found to be rich in diatoms when 
examined in slides 1 and 2 by Messrs. Keeley and Boyer, as mentioned 
on pages 40-41. Nos. 4 and 6 are analyses of samples from the same 
hand specimen, taken within 1 inch of each other, No. 4 showing the 
composition of unaltered white shale in which diatoms are visible, and 
No. 6 of the translucent, brittle, flintlike product of extremely local 
alteration. The next four indicate gradations in the products of the 
metamorphism. The last analysis (No. 11) represents limestone 
typical in lithologic appearance of the limestone of the Monterey. 
