ACADEMY OF NATURAL SCIENCES. 349 



Professor Silliman read the following paper : 



Notice of a peculiar mode of the occurrence of Gold and Sil- 

 ver in the Foot-Hills of the Sierra Nevada, and especially 

 at Whisky Hill, in Placer County, and Quail Hill, in Cala- 

 veras County, California. 



BY B. SILLIMAN. 



In the search for ores of copper which occurred in California in what is now 

 known as the " Copper Belt " of the Lower Sierras, deposits of " Iron Rust," as 

 they were called by the'miuers, were observed at numerous points far below the 

 range of the main gold belt of the Sierras. Several of these ochraceous depos- 

 its had been previously " located" by prospecting miners for gold, before there was 

 any knowledge, or suspicion even, of the existence of ores of copper in connec- 

 tion with them. It was a matter of common observation that certain gulches, or 

 watercourses in the neighborhood of these rusty deposits, were rich in placer gold, 

 having been worked for gold from an early date. The search for copper in 

 this kind of deposit was not commercially successful, although there were ship- 

 ments of green and blue carbonates of copper, red oxide and metallic copper, to 

 a limited extent from both the localities here referred to, the metal from which 

 was known to contain a notable value of gold and silver, stated to be about 

 fifty dollars to the ton of ore. This search for copper has, however, opened up 

 these deposits so as to display their character in a conspicuous manner. 



The rocks appear to have been originally talcose and cbloritic schists, some- 

 times micaceous, inclosing masses of argil] ite, and of quartz which appears to 

 have been massive enough at certain points to assume the character of a vein, 

 and parallel to the stratification which has the usual north-western strike and 

 easterly dip of the region. All this mass of material which at Quail Hill is cer- 

 tainly three hundred feet wide, and possibly twice that, and with a linear extent 

 exceeding one thousand feet, appears to have been very highly impregnated or 

 mineralized by sulphurets, chiefly of iron, with a portion of copper, zinc and 

 lead. The sulphurets have undergone almost total decomposition throughout the 

 entire mass, leaving soft ochraceous deposits of a rusty red and yellow color, and 

 staining the rocks with brilliant colors, a peculiarity which the miners have 

 characterized by the name of " Calico rocks." This decomposition or oxida- 

 tion of the sulphurets, has extended to a point as low as atmospheric influences 

 extend, or probably to a point where water is permanently found, which at 

 Quail Hill is assumed to be about 170 feet below the outcrop of the mass, or 

 crest of the hill. Dykes of porphyry and of other rocks, commonly called 

 intrusive, are seen dividing these great ore channels in a direction conforma- 

 ble to the line of strike. But the decomposition which has affected other por- 

 tions of the ore channel, appears also to have changed them, for they are found 

 to be reduced completely to the condition of kaolin and lithomarge, or kin- 

 dred alterations of feldspathic rocks. The outlines of the feldspar crystals are 

 still easily distinguished, although the mass of the dykes is completely friable. 



