THE PACIFIC SLOPE. 249 



what obscure. In California the veins occupy undoubted fissures 

 in the slates. The largest and best known is the so-called Mother 

 Lode, which is a lineal succession of innumerable larger and 

 smaller quartz veins that run parallel with the strike, but which 

 cut the steep dip of the slates at an angle of 10. It was doubt- 

 less formed by faulting in steeply dipping strata. The wall rocks 

 of the California veins are serpentine, diabase, diorite, and granite, 

 as well as slate, for all these enter into the western slopes of the 

 Sierras. The serpentine is probably a metamorphosed igneous 

 rock, while the diabase and diorite form great dikes. Considerable 

 calcite, dolomite, and ankerite occur with the quartz, and very 

 often it is penetrated by seams of a green chloritic silicate, which 

 is provisionally called mariposite, as it is probably not a definite 

 mineral, but rather an infiltration of decomposition products. The 

 quartz veins vary somewhat in appearance, being at times milk 

 white and massive (locally called " hungry," from its general bar- 

 renness), at times greasy and darker, and again manifesting other 

 differences, which are difficult to describe, although more or less 

 evident in specimens. The richer quartz in many mines is some- 

 what banded, and is called ribbon quartz. The quartz has been 

 studied in thin sections, especially in rich specimens, by W. M. 

 Courtis, who shows that fluid or gaseous inclusions of what is 

 probably carbonic acid are abundant. In rich specimens the cavi- 

 ties tend to be more numerous than in poor, but more data are 

 needed to form the basis of any reliable deductions. Some quartz 

 showed evidence of dynamic disturbances. The walls of the veins 

 are .themselves impregnated with the precious metal and the at- 

 tendant sulphides. The rich portions of the veins occur in chutes 

 to a large degree. 



2.12.14. The great Mother Lode is the largest group of veins 

 in California. It extends 112 miles in a general northwest direc- 

 tion. Beginning in Mariposa County, in the south, it crosses 

 Tuolumne, Calaveras, Amador, and El Dorado counties in succes- 

 sion. It is not strictly continuous nor is it one single lode, but 

 rather a succession of related ones, which branch, pinch out, run 

 off in stringers, and are thus con^lex in their general grouping. 

 Over 500 patented locations have been made on it. Whitney has 

 thought it may have originated from the silicification of beds of 

 dolomite, but others regard it, with greater reason, as a great 

 series of veins along a fissured strip. The veins are often left in 

 strong relief by the erosion of the wall rock, and thus are called 



