130 



University of California. 



[Vol. 2. 



in which orthoclase is very abundant in large crystals and carlsbad 

 twins that make the rock decidedly porphyritic. Mr. H. W. 

 Turner has described a "granite-porphyry" from the Sierras 1 of 

 Butte County, California, that at first appears to resemble that of 

 the Coast Ranges. It appears, however, for the most part to be 

 confined to dikes, or at least already very limited. The pheno- 

 crysts are said to be of quartz and plagioclase. East of the 

 Yosemite Valley and at other places in the Sierra Nevada 2 porphy- 

 ritic granite occurs which bears a much stronger resemblance to 

 that of the Coast Ranges. According to Professor Lawson 3 there 

 is some resemblance between some of the granite of the Coast 

 Ranges and the " granodiorite " of the Sierra Nevada. Writing of 

 the rock from near Monterey he says: "The ground-mass of the 

 rock certainly belongs to that intermediate type for which Becker 

 has proposed the term granodiorite." Perhaps there is also some 

 resemblance to be found in the hornblende-bearing facies of 

 Montara Mountain. 



On the whole, however, there appears to be something of 

 contrast in the types most characteristic of the Sierras and of the 

 Coast Ranges. Basic granites of the types common in the Sierras 

 are not much known in the Coast Ranges, while on the other hand 

 the acid biotite granites, such as have been described from the Coast 

 Ranges, are relatively much less abundant in the Sierras. Yet too 

 little is known of either region to make any general comparison 

 either satisfactory or safe. 



PRE-GRANITIC CRUST. 



It seems a little remarkable that so few remnants of the ancient 

 crust, into which the granites of the Coast Ranges arose, have been 

 definitely recognized as such. There are traces of its rocks found 

 in the conglomerates of the Tertiary and older periods in many 

 places where such beds occur, but there are few, if any, extensive 

 formations that have been clearly shown to have formed a part 



x i7th An. Rept. U. S. Geol. Sur., pp. 572, etc. 

 2 14th An. Rept. U. S. Geol. Sur., pp. 478-480. 

 3 Bull. Dept. Geol. Univ. Cal., Vol. 1, p. 15. 



