RHYOLITE OP MAHOGANY HILLS. 137 



OH the west spur of Combs Peak, in beds dipping to the northeast, 

 occurs a belt of calcareous shales about 150 feet in width, carrying a rich 

 and varied fauna quite similar to the fossil-bearing shale belts of Atrypa 

 and Brush peaks and with a nearly identical fauna. On page 7<> will be 

 found a list of the Combs Peak fauna, together with those of the other 

 peaks, showing the strong parallelism in the life from the three localities. 

 The precise locality from which this fauna was obtained is designated on 

 the map. All the beds on the north slope of Combs Peak belong to the 

 east side of the synclinal fold, dipping into the mountain and passing 

 beneath the beds which form .the summit. 



Browns Canyon, at the base of the mountain, lies in the axis of an 

 anticlinal fold, the beds on the north side dipping to the northeast at angles 

 seldom exceeding 20. At the head of this canyon, along the axis of the 

 fold, occurs a body of compact rhyolite, which has for the most part been 

 extravasated on the south side of a local line of faulting. It forms a hill 

 about 250 feet in height, whose outlines are sharply denned by drainage 

 channels which almost completely surround it on all sides. The slopes of 

 the hill are strewn with fissile, sherdy fragments of rock characteristic 

 of the entire mass. The rhyolite has a microcrystalline groundmass, with 

 but few microscopic crystals of gray quartz, brilliant biotite flakes, and 

 occasional dull orthoclases. In the middle of this rhyolite is an irregular 

 exposure of Nevada limestone about 100 feet in thickness, indicating that 

 the greater part of the lava is only a thin flow over underlying limestones. 

 It is the single instance of a rhyolite exposure observed in Mahogany Hills 

 east of Yahoo Canyon. 



Temple Peak. From this rhyolite body the limestone hills rise gradually 

 to the northeast in gentle, flat topped spurs, culminating in Temple Peak 

 (8,398 feet), the highest point between Browns and Denio canyons. 

 Across this limestone body, from Browns Canyon to Dry Lake, the strata 

 dip persistently to the northeast, with a northwest and southeast strike. 

 The limestones at the summit lie inclined at angles seldom exceeding 5, 

 but are distinctly bedded, and in physical habit and sequence of strata 

 resemble those about midway in the Nevada limestone epoch. The same 



