Geology of California. — Turner. 311 
a mile from the Mother lode. It has very much the same appear- 
ance as the vein matter of the lode, except that there is no mari- 
posite. It is seamed with small veins of quartz and in surface 
decay produces the same red oxide of iron. The onh' real differ- 
ence is that the process of substitution is not so complete as in 
the Mother lode. Dikes that have undergone a partial change 
often occur penetrating the Mother lode vein matter, and at times 
they are slightly impregnated with mariposite. " 
Mr. Fairbanks' theory is a very plausible one, and it would 
seem probable that a thorough study of the Mother lode material 
and of this igneous mass b}' means of their sections, would sub- 
stantiate this view if true. 
Stratigraphy and Succession of the Rocks of the Sierra Nevada in Cal- 
ifornia; by James E. Mills; Bull. Geol. Soc. Am., vol. 3, pp. 413-444. 
Mr. Mills in this paper divides the rocks of the Sierra Nevada 
into three groups: 
Pre-Mesozoic, consisting of sedimentary slates and quartzites,* 
and eruptive granite. 
Lower Mesozoic, consisting of slates, greenstones and lime- 
stones. 
Upper Mesozoic, consisting of thinly laminated argillites (clay- 
slates and argillaceous schists) and serpentine. 
According to Mr. ^Nlills, granite is the chief pre-Mesozoic rock. 
His evidence of its age consists in his not having found it intru- 
sive in the Mesozoic rocks and in having found pebbles of it 
in a Mesozoic conglomerate (p. 429). This evidence, if correct, 
is entirely sufficient, but must apply to ver}' little of the granitef 
of the Sierra Nevada. The writer found the granite at Mount In- 
*Quartzite is perhaps properly defined as a silicified sandstone in 
which the original quartz grains have been enlarged by the addition of 
secondary silica so that there are no longer interspaces between them, 
but they either dovetail into one another, or present a true allotrio- 
morphic structure. Mr. Mills, however, uses the terra to indicate almost 
any highly siliceous rock. Thus on p. 42.5 both diabase and sei"pentine 
"are still further frequently altered to quartzites." Again on p. 423 he 
says: "In both cases the quartzlte is probably a product of alteration 
of the groTiite itself." This use of the term quartzite is still further 
exemplified on p. 440. 
fThe granite of the Sierra Nevada contains but a small amount of 
alkali, and is more correctly called a quartz-mica-diorite. Dr. Becker 
has introduced the term cfranodloritc for the alkali-poor granitoid rocks 
-of the Sierra Nevada. (See the text that accompanies the geological 
maps of the Gold Belt now being issued.) 
