1922] Vaughan: Geology of San Bernardino Mountains 351 



Archaean sediments so commonly pictured from the sections of the 

 Great Lakes region (fig. 2). The local nature of all this formation is 

 striking, for within a hundred yards one may pass from the clear-cut 

 uniformly dipping strata to the contorted mass. These occurrences 

 are usually found near an intrusion of granite which itself has often 

 taken on so similar an appearance that positive identification is diffi- 

 cult or even impossible. A specimen from this ridge which was thought 

 to be a fine-grained intrusive proved under the microscope to be a 



Fig. 2. Metamorphosed and contorted Saragossa quartzite at east end of 

 Baldwin Lake. 



quartz-mica schist. It is a mosaic of quartz containing small flakes 

 of sericite, green and brown biotite, and a few grains of titanite and 

 magnetite. 



Farther southeast in the section exposed by Arrastre Creek the 

 quartzites, particularly the more impure layers, have been altered to 

 schists and these are cut by granites and later by many pegmatite 

 dikes. In lower Arrastre Creek the Arrastre quartzite has been altered 

 and intruded by granites and cut by pegmatite dikes in such a manner 

 as to be quite comparable to the most complex relations found in any 

 part of the great schist area on the south side of the range, and even a 

 microscopic examination shows fully as great changes from the original 

 sediments. (See Arrastre Quartzite.) This mass extends east beyond 

 Rattlesnake Canon, where it is dispersed by intrusions of granite. 

 East of Rattlesnake Canon, three miles south of Mound Spring, the 

 schist forms the end of a syncline in which limestone rests. Here 

 again the schist is cut by granites which also have a well developed 



