Vol. 4] Lawson. — The Robinson Mining District. 



357 



Turquois occurs sparingly in the ore-bearing porphyry of the 

 Ruth Mine. 



Galena occurs somewhat abundantly in silver-lead deposits to 

 the north of the Ruth and to the north of Lane Valley. 



Molybdenite thin films in the minette of the Ruth Mine. 



Calamine found rather commonly in the zone of oxidation of 

 the silver-lead deposits to the north of the Ruth. 



Fluorspar gangue mineral of the silver-lead deposits and also 

 in nests in the ore-bearing porphyry near the head of Lane 

 Valley. 



Calcite a gangue mineral in the silver-lead deposits. 



Magnetite in considerable bodies at the Ruth, Copper Flat, 

 and Pilot Knob at the contact of the ore-bearing porphyry with 

 limestones. Apparently only on the lower side of porphyry 

 intrusive. 



Limonite same occurrence as magnetite but more limited: 

 also common in the oxidized zone of the pyritiferous rocks. 



Oarnet common at the contact of monzonite, monzonite por- 

 phyry, and ore-bearing porphyry with limestones; both light 

 yellow garnet, grossularite, and a red lime-iron garnet, andra- 

 dite,- occur. The andradite also occurs in the quartz blout below 

 the zone of oxidation. 



Chiastolite in fragments of black metamorphic slate enclosed 

 in obsidian on the Josephine claim. 



Rhodochrosite ; presence inferred from the pink color of cer- 

 tain limestones which weather to a brownish black color and give 

 reactions for manganese. 



Wad rarely found in the porphyry of the Ruth Mine. 



Talc occurs in a notable body in a tunnel run into the ore- 

 bearing porphyry on the west side of a gulch about 500 yards 

 west of the head of Lane Valley. 



Gypsum occurs as a current deposition on the rubble of cer- 

 tain dumps near the head of Lane Valley. 



Opal sparingly in small veins in silver-lead deposits. 



Biotite a notable occurrence in the form of nests in the ore- 

 bearing porphyry in Copper Flat mines and to a much less ex- 

 tent in the Ruth Mine. 



University of California, 

 May, 1906. 



