BULLION OASON. 175 



their existence by the recurrence of beds, which seem to be identical both 

 individually and serially, at higher and higher levels up the canon. 



As we ascend Bullion Canon from Marysvale we observe on either side 

 a hard quartzitic rock well bedded in massive layers, exhibiting consider- 

 able metamorphism. It is also somewhat variable in the dip. The strata 

 incline upward at first, but soon flex easily back until the dip is westward. 

 The thickness of the series seems to be very considerable, though the ap- 

 parent thickness may be partly due to repetitive faults of small shear. At 

 a distance of about 3 miles from Marysvale and 2,G00 feet above that vil- 

 lage, we come upon the volcanic series. A mass of dark-colored liparite 

 rests upon the quartzitq, having a thickness of about 450 feet. About 500 

 feet higher the quartzite reappears, being probably the same bed as below, 

 but thrown up by a minor displacement, and it is covered by the same or 

 a similar sheet of liparite The quartzite, however, is more altered than 

 the jDOition of it below, and in general as we ascend from Marysvale 

 through the quartzitic beds the signs of increasing alteration are unmistak- 

 able. From this point upwards eruptive rocks alone are seen. The lower 

 masses are dark liparites, with abundant quartz and monoclinic feldspar and 

 decomposed hornblende. Still higher rocks of a porphyritic texture and a 

 dark purplish hue lie in great volume. They have a striking resemblance 

 superficially to the argilloid trachytes of the central and eastern plateaus, 

 but contain abundant quartz, and the microscope confirms their rhyolitic 

 character. These two groups of eruptions are separated by local conglom- 

 erates derived from the older of them, and the surface of the latter is seen 

 to have been much eroded, indicating a considerable interval of time 

 between the periods of activity. The summit of the series consists of a 

 group of rhyolites (proper rhyolite), which contrast strongly with those 

 beneatli. They are very light colored, without crystals, and yet not hyaline. 

 They are highly siliceous, and exhibit in the thin sections a fibrolitic or 

 spherolitic groundmass of beautiful texture and very interesting. Some 

 of the specimens are exceedingly siliceous, and are resolved under the 

 microscope into an aggregation resembling very fine-grained quartzite and 

 appear to be quite abnormal. The light-colored masses are generally true 

 rhyolites of no uncommon kind. This rock forms the lofty peaks crown- 



