Geology. 271 
These last occur in a bank fronting the 
1 y, and which is partly undermined by the surf. The bank is filled 
‘ with shells, and the principal stratum is about 30 feet above tide. 
he fossils from the sandstones along Carrizo creek, near the point 
: where it spreads out and is lost in the desert, are all new and of Mio- 
cene age. 
: Miocene formation appears, therefore, to flank the Peninsula 
Sierra on both sides in the latitude of San Diego, and to underlie the 
this chain. Those on the desert side form a stratum four or five feet 
thick of shells alone, consisting almost wholly of the genera Ostrea, 
: mia and Pecten; while on the west side, bordering the Pacific, 
there 1S a greater variety of genera and species; shells of the genera 
Cardium, N ucula, Corbula, Tellina, Mactra, Natica and Trochita being 
eae 
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perfect state, and, also, a small shark’s tooth. The shells were proba- 
bly of the genera Trochus and Turritella. Numerous specimens of 
ane Were also found at that place, imbedded in the compact sand- 
one, 
the surf. They are inclosed in a matrix of bluish-green sand, resem- 
bling in color and composition the blue sandstone of the bay. It is, 
Wever, more friable, and seems to consist of the debris of the strata. 
town of Monterey is built over the line of junction of the come 
a e 
of tertia: strata, remar 
4 18) 
aid of a glass thousands of these little shells can be 
‘uted surfaces of the rock. 
