EAST HUMBOLDT RAJh^GE. 529 



broken by numerous canons, many of them quite remarkable, which show 

 characteristically the manner in which heavy bodies of limestone, when gently 

 inclined, may be eroded into narrow, deep canons, with nearly precipitous, 

 walls. The photograph, reproduced on Plate XVII, represents this type of 

 structure, as seen in Blue Canon, with nearly sheer cliffs from 1,400 to 

 1,800 feet in height, standing out boldly above the Quaternary plain. 



Wrapping around the granite mass, which occupies the whole of Fre- 

 mont's Pass, are found the limestone beds, forming the extreme northern 

 extension of the main body. On the eastern foot-hills, about a mile and a 

 half north of the pass, the limestones stand nearly vertical, and appear as a 

 mere thin bed, which rapidly dies out against the granite to the north 

 Coming south of the pass, the angle of inclination decreases from 50° to 40°, 

 and falls off gradually to 22 °, with a southeast dip. At the high peaks back of 

 Cave Creek, a recorded dip gives 16° to the southeast, and still farther to 

 the southward the beds become nearly horizontal. They again rapidly rise in 

 dip till, north of Hasting's Pass, and west of Fort Ruby, they reach an angle 

 of 16° to 20° ; this time, however, inclined to the northeast. It will be 

 seen, therefore, that, while the general dip is eastward, there is a gentle 

 north and south synclinal structure. 



About a mile south of Fremont's Pass, these limestones rapidly thicken, 

 and are underlaid by 800 to 1,000 feet of white to brownish-white, highly- 

 laminated quartzite. It is usually a compact, highly vitreous rock, the 

 brown color being derived from the presence of small amounts of iron scat- 

 tered throuo'h it, or else occupying thin, narrow seams. This whole series, 

 the quartzite and overlying limestone, is distinctly unconformable to the 

 granites. In the canon next south of Fremont's Pass is seen a good exhibi- 

 tion of the conformable series, with the quartzites dipping 18° to 20° to the 

 southeast. The transition from the quartzites to the limestones is made in a 

 very short distance, without any noticeable interstratification of beds. The 

 quartzites appear a little calcareous and the limestones somewhat siliceous, 

 but the transition is made by a rapid passage from one to the other. The 

 limestones are of a very light gray and grayish-buff, and these colors prevail 

 for about 1,600 feet upward in the series, when the beds are usually of a 

 dark-grayish hue, and the bedding nmch heavier than in the zones below. 



34 D G 



