DESCRIPTION OF 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 caiion San Juan. 



a represents the sandstones of Salinas valley, with Dosinia reposing on the serpentine and 

 magnesian rocks of Point Pinos. 



G, the serpentine crest of Point Pinos range, lying east of 



d, the orthose granite of that range ; also, the granite of Gavilan. 



b, metamorphic limestone, lying on the east edge of the Salinas valley and underlying the 



whole Canada San Juan. 



e, the alluvial clays and gravels of the Salinas valley, its upper edge worn out so as to afford 



three levels. 

 Pig. 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. 



to 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 hy 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, h, c, of the Gavilan 

 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 hy 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. 



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