MONTEZUMA KANGE. 755 



the plain. In its field habit, modes of weathering, and geological relations, 

 it closely resembles the more important body to the northward. This latter 

 granite occupies the central mass of that portion of the Montezuma Range 

 lying north of Antelope Peak. It is about 15 miles in length, and almost 

 entirely surrounded by beds resting unconformably upon it, made up of 

 fissile slates, calcareous shales, and limestones, referred to the Jurassic age. 

 It possesses a medium-grained texture, a light-gray color, and the normal 

 mineralogical composition, carrying considerable amounts of well-developed 

 brilliant hexagonal plates of biotite. 



North of Indian Pass, the Jurassic is the prevailing formation, wrap- 

 ping around the granite bodies on the west and north, and dipping, except 

 in local instances, to the west and northwest. The most favorable place 

 for studying these beds is at Antelope Peak, where they reach a devel- 

 opment of nearly 4,000 feet, exposed along the walls and slopes of French 

 Canon. The beds strike diagonally across the range, dipping, however, at 

 very varying angles, owing to the intrusive masses of diorite and porphyry, 

 which have tlu-own them up to 75° and 80°, with a strike of north 25° 

 east. On the summit of Antelope Peak, they strike from north 25° to 

 30° east, and dip 35° to 40° to the northwest, the beds falling away grad- 

 ually toward Indian Pass. The slates and shales have a bluish-gray color, 

 a thin lamination, and are frequently very brittle. In composition, they 

 are generally arenaceous, passing into thin beds of compact sandstone. 

 At times, the strata become gradually calcareous, and the rock passes into 

 a well-defined limestone, rarely, however, more than a few feet in thick- 

 ness, but of a deeper blue color than the slate rocks. West of Antelope 

 Peak, the strata are considerably disturbed, curving around the southern end 

 of the granite, beyond which they again dip to the westward, forming the 

 main ridge. Here they follow a somewhat sinuous course, trending ofi^ to 

 the northwest for about 12 miles, until beyond the influence of the rigid 

 granite, when the ridge takes a nearly north and south direction, which it 

 maintains beyond the limit of this exploration. The last fifteen miles con- 

 sist almost exclusively of low hills of slate and shale, which rise hardly 

 more than 900 feet above the eastern valley, toward which they fall oft' 

 somewhat steeply, but more gently to the westward. Three miles below 

 the upper limit of the map, the hills are separated by a low pass or depression 



