Annual report of the State Mineralogist for the year ending ... . able to visit many places in the county from whereextensive finds of gold, silver, iron, and bismuth have been reported. A feature of the topography and geology of the northeastern portionof the county is the basaltic table mountain, which runs almost parallelwith and near to the San Joaquin River. Although this table extendsfor many miles at intervals, the point where I have had opportunitymore closely to examine it was in the vicinity of Auberoy Post Office, inT. 10 S., R. 22 E. Here the table has an altitude above the road fr
Annual report of the State Mineralogist for the year ending ... . able to visit many places in the county from whereextensive finds of gold, silver, iron, and bismuth have been reported. A feature of the topography and geology of the northeastern portionof the county is the basaltic table mountain, which runs almost parallelwith and near to the San Joaquin River. Although this table extendsfor many miles at intervals, the point where I have had opportunitymore closely to examine it was in the vicinity of Auberoy Post Office, inT. 10 S., R. 22 E. Here the table has an altitude above the road from 192 REPORT OF THE STATE MINERALOGIST. Little Dry Creek of about six hundred feet, and a width on top whichvaries from a mile to a few hundred feet. The capping rock of this tableis basalt, columnar in structure, while underneath is a volcanic ashoverlying a bed of gravel, which contains in places some gold, but hasnot been extensively prospected. The following sketch shows the com-parative position of the auriferous gravel and the trend of the basaltictable:. Extending north and east, I am informed that the table continues, inplaces, to the regions of the Minarets, where much of the surface iscovered with pumice, broken into small pieces, and from a foot to sev-eral feet in depth. Through this basaltic table, or, better, through thegranite underlying it, runs a quartz vein, on which are located severalmines. On the south or east side is the Hoxie, or Herron Mine, thecourse of its ledge being north 15 degrees east, dipping to the west at anaverage dip of 45 degrees. The fissure has an average width betweenthe Avails of from four to six feet, and the wall rocks clearly show theaction of heat. While the ledge has but an average of eighteen inchesin width, and the fissure from four to six feet, the intervening space isfilled with a compact mass of micaceous quartz sand. The mine isopened by a tunnel and two shafts. The tunnel is eighty feet in lengthand cuts the ledge at right a
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Keywords: ., bookcentury1800, booksubjectgeology, booksubjectminesandmineralr
