1922] Vaughan: Geology of San Bernardino Mountains 353 



where they lie conformably below the Furnace limestone. Both 

 formations at this point dip 35° to the southwest. The limestone 

 grades down into calcareous mica schist about ten feet thick, below 

 this is a stratum of massive quartzite six feet thick, which in turn is 

 underlain by black and grey mica schists with quartzose layers grad- 

 ing down into rather thin-bedded quartzite; i.e., individual strata are 

 seldom six inches thick. As one crosses the strike by going down 

 Arrastre Canon for half a mile the dip increases to 65°, and a rough 

 estimate of the thickness of the quartzite from these data is about 

 2500 feet. The total may be much greater, but this cannot be more 

 accurately determined, as the sediments are badly broken up by intrud- 

 ing granites. The impure quartzite is so altered and the granite is so 

 gneissic that the two are often indistinguishable. The granites them- 

 selves are very heterogeneous and, together with the sediments, form 

 a mass so complex as to defy description. A block consisting of quartz- 

 ite intruded by lamprophyre was seen sunken into a dark hornblende 

 granite. Irregular pegmatite dikes cut the mass and they in turn are 

 cut by other granites. 



A comparison of the Arrastre and Saragossa quartzites brings out 

 several important differences. Most of the Arrastre is thin-bedded, 

 individual beds being less than six inches thick, and there are no beds 

 up to five and ten feet of pure quartzite such as found in the Saragossa. 

 There is no. pure sacchroidal quartzite, no great variety such as coarse 

 angular grits, pebble conglomerate, cross-bedding, etc., all of which 

 are prominent features of the Saragossa. 



From Arrastre Creek the Arrastre quartzite can be followed to the 

 southeast as far as Rattlesnake Canon. The contact with the granite 

 on the south is so straight that it at once suggests faulting. Apophyses 

 from the granite cut the quartzite, but these may well have been faulted 

 off from the main mass. The best evidence is the contact just north 

 of Granite Creek, where it seems impossible that any other than a 

 fault contact could follow down the hill in such a straight line. Along 

 the northern boundary of the quartzite the association with the intru- 

 sive granitic rocks is so intimate that one can hardly tell where to draw 

 the line of demarcation ; numerous blocks of quartzite, some several 

 hundred feet across, are isolated by the intrusives. 



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

 quartzose schists form the end of a syncline in which limestone rests. 

 They are intruded by granitic rocks on which schistosity has also been 

 impressed. The mass as a whole is very complex, but, since it agrees 



