The quicksilver resources of California . fourth of an inch widecutting throughthe sandstone canbe seen. The ac-companying pho-tograph (No. 11)of a thin section(enlarged) con-clusively provesthe serpentiniza-tion of the sand-stone. In the beltbetween the ser-pentine and theChico, a great partof the sandstoneis so thoroughlyrecrystallized bymetamorphic ac-tion that it is verydifficult to decide in the field whether the material is meta-morphic sedimentary^ or eruptive. In the lower part of Clear Creek near its entrance into theSan Benito, a conglomerate is found on the hills, containingpebbles
The quicksilver resources of California . fourth of an inch widecutting throughthe sandstone canbe seen. The ac-companying pho-tograph (No. 11)of a thin section(enlarged) con-clusively provesthe serpentiniza-tion of the sand-stone. In the beltbetween the ser-pentine and theChico, a great partof the sandstoneis so thoroughlyrecrystallized bymetamorphic ac-tion that it is verydifficult to decide in the field whether the material is meta-morphic sedimentary^ or eruptive. In the lower part of Clear Creek near its entrance into theSan Benito, a conglomerate is found on the hills, containingpebbles of all kinds of rocks, including serpentine. Thisregion must have been a lake of large dimensions, as conglom-erate is found 1100 feet above the level of Hernandez. Anotherappearance of conglomerate is found overlying metamorphicsandstones and shales, at an elevation of 4700 feet (2150 feetabove Hernandez), forming the highest point of the mountaincluster, which forms the big bend of San Benito Creek, southof the Picachos (Dominic Peak).. PHOTO No. n. Thin Section of Sandstone and Serpentine from Xew Idria District. 41 Diameters. *i>llciili .ilcyivJijy t: ^A/. n t ? I r jh cr o af y T1 SAN BENITO COUNTY. 127 situated on the northeastern contact of the same belt of themetamorphic series. The serpentinization of the rock is veryirregular, and sometimes very light, ^vhile in other places therock is a talcose, bluish-green serpentine, with a more or lessconchoidal fracture. Inclusions of bodies of sandstone andshale are found in the serpentine. On a ridge over a mile long,having a course about S. 30° W., running from the divide southof the San Carlos, along the headwaters of Clear Creek towardthe Picachos, and at the surface entirely formed of serpentine,all gradations from sandstone to serpentine are found. In oneinclusion of a yellow sandstone, at least 100 feet b} 50 feet atthe surface, seams of serpentine over a fourth of an inch widecutting throughthe sandstone canbe seen.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectminesandmineralresou
