64 GREAT MOTHEB LODE OF CALIPOENIA. 



of the numerous mines which have been worked, either in the 

 mass of the vein itself, or in its immediate vicinity."^ 



Prof. Whitney thus describes it : — ''This powerful lode is 

 made up of irregularly parallel plates of white compact quartz 

 and crystalline dolomite or magnesite,f more or less mixed with 

 green talc ; and these plates, which somewhat resemble the 

 " combs " of ordinary lodes, are either in contact or separated 

 from each other by intercalated layers of talcose- slate. The 

 . quartz is chiefly developed in the central portion of the vein ; 

 and, from its colour and resistance to decomposition, it gives rise 

 to a very conspicuous outcrop, forming the crest of the hills, so 

 that it can be readily seen from a distance of several miles. The 

 dolomitic or magnesitic portion decomposes somewhat readily, 

 and it becomes a kind of " gossan," or a cellular ferruginous 

 mass, of a dark brown colour, often traversed in every direction 

 by seams of white quartz. The quartz is the auriferous portion 

 of the lode, although it is far from being uniformly impregnated 

 with gold, Most of the mines which have been worked, between 

 the Merced and the Stanislaus, are on the north-east side of the 

 Q-reat Quartz Vein, either in contact with it or in some parallel 

 band of quartz subordinate to, or at a little distance from it. 

 The talcose slate bands in the vein are often, themselves, more 

 or less auriferous." (Whitney, p. 46). 



The general dip and strike of the quartz corresponds with 

 that of the enclosing rocks. The most marked exception is seen 

 near Big Oak Flat, in Tuolumne Oo., where it cuts diagonally 

 across the beds both in strike and dip. In Mariposa Co., and 

 other places where the quartz is very largely developed, it loses 

 its platy structure, and appears in compact masses of 20, 40, or 

 more feet in thickness. Often, too, it sends o£f innumerable 

 branches and ramifications into the country rock. 



In general the gold occurs in the quartz, as already stated. 

 It is very often accompanied by small quantities of sulphurets, 



* The annual production of gold in California has a value of about 16 

 millions of dollars, of which about 8 millions are derived from mines proper, and 

 the remainder from the gravels. The Mother Lode is estimated to yield about 2 

 millions annually. 



f "In the only specimen which has thus far been chemically examined, the 

 supposed dolomitic portion proves to be an intimate mixture of quartz and mag- 

 nesite." — Whitney. 



