RELATIVE POSITION OF STRATA IN THE VALLEY. 41 



waters of the San Antonio, this bed was found to occupy a large surface and to be the uppermost 

 rock. Its dip, when first observed, was to the southwest, so that it lay on the west or Pacific 

 slope of the Point Pinos chain, which is here a series of low and broad hills. Underneath this 

 whitish clay rock lies a bed of conglomerate, made up of a clay paste cementing rounded and 

 broken pebbles of prase, hyalitic, jaspery quartz, obsidian and serpentine. The observed thick- 

 ness of this conglomerate was 80 feet. It contains no fossils. Below the conglomerate a reddish 

 sandstone grit was observed. This grit is one of the beds which repose on the east side of the 

 range, and dip under the Salinas river, and rises up again on the sides of the Gavilan range. 

 This constitutes the whole section of stratified rocks. The axial rocks did not appear exposed, 

 but the arroyos brought down, beside serpentine, obsidian, and trap, broken angular fragments 

 of gneissose rock and felspathic granite. So that a section of these hills would afford the 

 following details : 



Igneous rock. — Granite, gneiss, serpentine, obsidian, trap, in veins. 



Sedimeniary rock. — From below upward : Reddish sandstone grit ; conglomerate green, 

 quartzose ; whitish green calcareous and fossiliferous beds, in brown sandstone, with Dosinia 

 and Fecten. 



A section of the San Antonio hills and Salinas valley is given on Plate I, figures 1 and 3. 



The whitish green calcareous rock is met the entire length of the chain for 30 miles, termi" 

 nating a few miles south of Mission San Miguel, where they can be traced passing up the 

 Estrella river, and forming tlie side hills of the river bottom upon which the terraces are placed. 



The fossils found in the sandstones on the west side were: Dosinia -Monterey ana, Dosinia 

 Montana, Dosinia Subobliqua, Dosinia Longula, (vide Mr. Conrad's report ;) which extended from 

 the Salinas river, at Mr. Hill's, at the north extremity of the valley, to near the Mission San 

 Miguel, at the south end. Ten miles south of the junction of the Estrella and Salinas rivers 

 the valley of the Salinas may be said to terminate. The granitic rocks and sandstones of the 

 Point Pinos chain cross the river and form the western boundary of that stream for some miles 

 further south. 



The granitic rocks at this point are low hills, flanked by the sandstones, having a slight dip 

 to the southwest. By following the course of the river, which here comes from the S.S.E., a 

 small valley is reached — the valley of the Mission Santa Margarita. 



The geological structure of this valley was obtained very imperfectly, partly on account of its 

 great size and the rapid transit over it, but chiefly on account of the fogs, which for some days so 

 completely hid the plain as to render everything further off than 50 yards wholly undiscernible. 

 Fossils similar to those found on San Antonio hill slopes were found in the bed of the river n.ear 

 Mr. Hill's ranch ; so that this upper layer of the sandstones of the Point Pinos range extends 

 the whole length of the valley on its west side. They are, however, inferior to the beds con- 

 taining the Ostrea and Echinoderms of Santa Margarita valley. 



6 U 



