GEOLOGICAL SURVEY. OF THE TERRITOEIES. 169 



this first ridge we passed over tlie upturned edges of limestones, dip- 

 ping about northeast, and on the opposite side of the ravine, on the side 

 of the ridge which culminates in Mount Blackmore, there is also an ex- 

 posure of limestone, dipping in the same direction. The upper layers 

 have an inclination of about 30°, while the lower ones incline only 10°. 

 These limestones are capped with volcanic material, which seems at first 

 to have tipped them up and afterward crushed them. Mount Black- 

 more itself is a volcanic peak, and the nearness of the sedimentary 

 rocks to the center of volcanic action, which lies to the south or south- 

 east, has aiiected them to a great extent and thrown them into great 

 confusion. Taking our horses to the timber-line (9,550 feet) we finished 

 the ascent on foot with comparative ease. The rock of which the peak 

 is composed is basaltic in its character, of black and red colors. On the 

 summit it is very compact and massive, while below we find it laminated 

 and somewhat porphyritic. On the way up I found excellent specimens 

 of Hyalite in globular concretions, as clear as glass, coating the rocks 

 and making them look as though coated with ice. I also found Chalce- 

 dony and a yellow variety of opal resembling somewhat fire-opal. It 

 varies in color from a honey -yellow with a greenish tinge to a brownish 

 red. It is opaque; luster vitreous; hardness, 5; specific gravity, 2.172. 

 Considering its physical properties it might be distinguished as a 

 variety of opal between fire-opal and the ordinary semi-opal. I propose 

 for it the name of Blackmorite, from its locality, Mount Blackmore. An 

 analysis of it is as follows : 



Analysis. 



"Per cent. 



Loss at IIQOC 7.40 



Loss on ignition 2. 40 



Silica 85.20 



Iron oxide 2. 68 



Lime 1. 48 



Magnesia 0. 37 



Soda"* Trace. 



99.53 



The view from the summit of Mount Blackmore is grand in the ex- 

 treme. When we turn to the south we overlook an intensely rugged 

 country, studded with numerous sharp volcanic peaks. Quite near 

 the peak there is one point which looks as though it were once the center 

 of volcanic action, the sloping sides bearing a striking resemblance to 

 the sides of an old crater. To the north the field of vision is immense. 

 The valley of the Gallatin, from its sources at our feet to the Three 

 Forks, lies spread out before us, and beyond we could distinguish in the 

 dim distance even the Missouri. Here we could trace the layers of 

 limestone from Mystic Lake to Middle Creek, thence across the 

 Cottonwood, the next stream to the west, and thence across to the West 

 Gallatin. AH these streams have cut their way directly across the 

 strata at right angles to the strike. To the west we could see the Madi- 

 son Range, and on the east the snowy range of the Yellowstone. The 

 elevation of the peak above sea-level is 10,134 feet. The following 

 morning we followed Middle Creek to its sources, and found that the 

 valley abounded in most magnificent scenery, foliage, rocks, and numer- 

 ous water-falls and cascades combining to form the most beautiful pic- 



* By spectroscopic examination. 



