DESCRIPTION OE THE PLATES. 
PLATE I. 
Fig. 1.—Section across Monterey county, from the Pacific ocean, at Point Pinos, to San Joachin 
valley, in a line due east. This includes a section of the Salinas valley and the small 
valley of the canon San Juan. 
a represents the sandstones of Salinas valley, with Dosinia reposing on the serpentine and 
magnesian rocks of Point Pinos. 
c, the serpentine crest of Point Pinos range, lying east of 
d, the orthose granite of that range ; also, the granite of Gravilan. 
b, metamorphic limestone, lying on the east edge of the Salinas valley and underlying the 
whole Canada San Juan. 
c, the alluvial clays and gravels of the Salinas valley, its upper edge worn out so as to afford 
three levels. 
Fig. 2.—Section across San Luis Obispo county, showing the asphaltic group of San Luis 
valley, the structure of the Santa Lucia mountains, and the strata in Santa Margarita 
valley. 
a represents granitic rocks. 
c, serpentine lying at a high angle upon 
t, trappean and augitic rock. 
w show the veins of asphalt passing up through the bituminous group of San Luis Obispo 
valley. 
The Santa Margarita sandstones are shown included in a basin formed by the San Jose and 
Santa Lucia mountains ; these sandstones are inferior to the San Luis group. 
Fig. 3.—Section of the San Antonio hills, near the mission San Miguel, Salinas valley. The 
central axis is felspathic granite, d, upon which the sandstones a, b, c, of the Gravilan 
group repose conformably. On the east side of the range a bed of serpentine, s, inter¬ 
venes between the primary rock and the sandstones ; both the latter and the serpentine 
are cut through by dykes of felspathic (augitic) trap. This is the geological position of 
the auriferous region of these hills, a thin bed of talc slate accompanying the serpentine. 
In the bed, c, is found the four species of Dosinia; this bed, also, has on its lower portions 
the terraces of the Salinas valley, between missions Solidad and San Miguel. 
Fig. 4.—Section across the Santa Margarita valley, from the residence of Don J. d’ Estrada to 
the granitic hills east of the river. The house is on a low terrace on the west side of the 
valley, the horizontality of which is disturbed by trappean dykes, c, c. The strata, 
marked e, contain the Ostrea, Hinnites and Astrodapsis; f are the whitish-gray sandstones 
with Dosinia; g , brown and yellow sandstones, with gypsum and oxide of iron; and h, 
the coarse breccia conglomerate which lies next the primary, underlies the whole basin, 
and rises again on the opposite side near the summit of Santa Lucia. 
