W. Lindgren — Auriferous Veins of California, 203 



Sierra Nevada and which probably extend through southern 

 California far down into the peninsula of Baja California * 



The rock consists in typical development of feldspar, quartz, 

 biotite and hornblende with medium grained hypidiomorphic 

 structure. The soda-lime feldspars are usually considerable 

 and to a variable extent in excess of the alkali feldspars. The 

 silica varies between 60 and 73 per cent ; the amount of lime is 

 variable, but it rarely exceeds while it usually falls somewhat 

 short of the sum of the alkalies. While in some varieties which 

 cannot be distinguished from the others in the field, there is 

 more potash than soda, a frequently occurring relation is 

 2 per cent Ka 2 to 4 per cent Na 2 0. It will be seen that the 

 rock very closely approaches some quartz-mica-diorites and 

 often might be indicated by that name.f 



This term, however, besides being clumsy, does not suffi- 

 ciently express its close relationship to granite, brought out by 

 its frequently high percentage of silica and low percentage of 

 lime, by its variable percentage of alkali feldspars and by the 

 muscovite sometimes occurring in it. On the Survey maps of 

 the Gold Belt of the Sierra Nevada, of which district Mr. 

 G. F. Becker is geologist in charge, it has therefore been deter- 

 mined to indicate this rock as granodiorite, which term it is 

 hoped will find general acceptance. 



Age of the granodiorite — The granodiorite is later than the 

 quartzitic slates of Signal Peak or Red Mountain north of 

 Cisco, which have been extensively metamorphosed by it. As 

 these sedimentary rocks are the direct continuation of the 

 series which a few miles farther south at Sailor Canon have 

 been identified as Jura-Trias from the meagre fauna occurring 

 in them, the granodiorite evidently postdates that period. 



At Meadow Lake several interesting facies of the granodio- 

 rite occur. Near the diabase contact it appears darker and 

 more basic by increasing hornblende. West of Meadow Lake 

 from the Keystone mine up towards French Lake there is no 

 biotite, but at many places a monoclinic pyroxene appears and 

 the rock contains abundant titanite. At several places near 

 French Lake a peculiar augite-diorite occurs composed of 

 quartz, plagioclase and augite ; the areas of this rock, con- 

 nected by transitions with normal types, are distinguished by 

 the brilliant white color of the glaciated outcrops. 



Diabase. — An area of diabasic rock occupies the eastern 

 margin of the map, adjoined on the west by dark basic diorite. 

 It is sometimes, as at Meadow Lake dam, rather a uralitized 



* Compare: Petrographical notes from Baja California; W. Lindgren. Proc. 

 Calif. Acad. Sci., 2d series, vol. i, Part II, 1888. 



fit is also closely related to the Tonalite of Mount Adamello, but it did not for 

 several reasons seem advisable to adont that name. 



