of the Gold-fields of California. 327 



Some attention has also been recently directed to bands of 

 auriferous slate found in the copper-bearing band west of the 

 main gold-belt of the State, and in the foot hills of the Sierra. 

 Of the deposits of this description, those near Lincoln, in 

 Placer county, and at Quail Hill, in Calaveras, are the most re- 

 markable. 



In these localities the gold, instead of being obtained from 

 well-defined veins chiefly composed of ordinary quartz, is en- 

 closed in bands of siliceous slaty rock, extending north-west and 

 south-east, and dipping in conformity with the other strata of 

 the district. At the surface the Lincoln deposit is chiefly dis- 

 tinguished from the other slates of the neighbourhood by being, 

 in places, deeply stained by oxide of iron, and forms a low out- 

 crop of about 3000 feet in length and 200 feet in width. 



Where this has been cut into, it has been found to consist of 

 alternating bands of clay-slate stained by oxide of iron, and of a 

 friable sandy quartz still retaining distinct evidences of stratifi- 

 cation, and which under the microscope presents the appearance. 

 of a siliceous skeleton from which the more soluble constituents 

 have been removed by aqueous agencies. 



Through these bands, and running parallel with their strati- 

 fication, dykes of felspathic rock make their appearance, and 

 contain small opaque white crystals too much decomposed to 

 admit of identification. These, like the slate itself, contain gold, 

 but, in the case of the felspathic rock, in very small quantities 

 only. In the slate are also found lenticular masses of blende 

 and iron pyrites, both auriferous, with stains of carbonate of 

 copper. The whole mass of the stratified rock contains a cer- 

 tain amount of " free gold," although the seams vary consider- 

 ably in their yield> some of them affording mere traces, whilst 

 others assay as much as 3 oz. per ton. The whole of the gold 

 in the portions of the deposits as yet worked is in a " free " 

 state; but it is probable that below the water-level it will be 

 found associated with various sulphides, by the decomposition of 

 which in the upper portions the precious metal has become libe- 

 rated. The pyrites and blende, in addition to gold, afford by 

 assay a small quantity of silver per ton ; and particles both of 

 native silver and native copper may be extracted by washing the 

 decomposed slates. 



As a general rule, the quartz lodes of California have not been 

 found to be more subject to impoverishment in depth than other 

 mineral veins, some of them having been worked on their dip for 

 a distance of above 1200 feet without any diminution of their 

 yield having taken place. 



In order to determine the chemical and physical composition 

 of quartz forming the gangues of some of the principal auri- 



