MINERALS AT NEW ALMADEN. 315 



mercury), pyrite, quartz, calcite, and dolomite, and more or less closely 

 associated masses of bituminous matter. Accompanying the deposits is a 

 small amount of chalcedony or opal, usually black in color; but this sub- 

 stance is much less abundant here than in the greater part of the northern 

 mines. Dolomite is more prevalent as a gangue mineral here than in most 

 quicksilver districts, a fact probably not unconnected with the unusual 

 quantity of limestone in the sedimentary rocks. The croppings of the de- 

 posits are to a large extent composed of dolomite in botryoidal masses, 

 instantly seen to be secretions, and not sediments. Besides the minerals 

 enumerated, Prof. W. P. Blake reported mispickel in the upper working 

 of the New Almaden.^ This mineral was extremely abundant in the great 

 Peruvian mine and its existence at New Almaden is not at all improbable. 

 No one seems to have observed it here since 1854, however; for Prof B. 

 Silliman- in 1864, Mr. Goodyear^ in 1871, and my party in 1885 failed to 

 meet with it. Neither is it mentioned by Mr. G. RoUand." Professor Blake 

 also states that gold has frequently been found in small quantities in this 

 mine. This, too, is far from improbable, but it has not been verified 



The rocks associated with cinnabar in this district include every 

 variety of the metaraorphic series. Where the rock happens to be a per- 

 meable sandstone, impregnations have resulted. Elsewhere the ore seems 

 to occur exclusively in crevices in the rock, nor are the cracks invariably 

 filled, so that (piartz and carbonates frequently show surfaces covered with 

 crystal faces. In some cases quartz reddened throughout by cinnabar 

 occurs in this manner. I was unable to perceive any indication that ore 

 had been deposited by substitution or that the rock had iiiflnenced the 

 deposition of ore by its chemical properties. Ore is found with nearly 

 equal frequency in contact with various rocks and the existence of fissures 

 appears to have been the necessary and sufficient condition for the deposi- 

 tion of cinnabar and gangue minerals. The rock, then, influences the 

 occurrence of ore mechanically, thougli indirectly. Wliere disturbance of 

 the country resulted in the formation of open fissures or of ground present- 



' Am. Jour. Sci., 2d series, vol. 17, 1854, p. 438. 



'Ibid., vol. -.$8, 1864, p. 192. 



' Geol. Survey Califoruia, Geology, vol. 2, appeiidi.K, p. 99. 



■• Annales des mines, vol. 14, 1878, p. 384. 



