48 GEOLOGICAL SURVEY OF THE TERRITORIES. 



It is really an expansion of one of the branches of the Gallatin, about 

 one-fourth of a mile wide and three-fourths of a mile long. The scenery 

 all around it is very attractive, and Mr. Jackson succeeded in securing 

 some most excellent photographs. The hills, immediately surrounding 

 the lake, and, indeed, all the lower hills, are made up of sedimentary 

 rocks, and just on the shore of the lake is a considerable thickness of 

 grayish-brown arenaceous limestone filled with fossils, as Camptonectes 

 hellestriata, Pinna, Modiola, Myacites,PJiolodomya, and others. A patient 

 search at this locality would have been rewarded with many more species, 

 but enough were secured to fix the age of the beds as Jurassic beyond 

 a doubt. A group of strata once fixed in the scale by such an array of 

 evidence, forms a horizon which may be extended, with certainty, in 

 every direction for a great distance, even though the usual fossils may 

 not be found. The stream that comes into the lake passes through a 

 deep gorge, walled on either side with Carboniferous limestones. But 

 to the west and north, the mountains rise in rounded dome or cone-like 

 peaks, 1,200 to 1,500 feet, and in a few instances 2,000 feet above the 

 valleys below. These high mountains are composed of volcanic mate- 

 rials, a core, as it were, of more or less compact basalt, with volcanic 

 breccia all around it. Huge masses of this volcanic breccia have fallen 

 down into the valley and around the lake. High up on the sides of the 

 mountains, in some places, the igneous rocks present the appearance of 

 strata, which have suddenly been poured out in beds, and cooled 

 in separate layers, and these layers incline at moderate angles, as if 

 they had been acted upon by subsequent action of the volcanic forces. 

 All the lower hills, which are comparatively sloping and underlaid with 

 sedimentary rocks, rising to the height of 200 to 500 feet, are covered 

 thickly with vegetation, mostly pines, but the higher volcanic ridges 

 are dark, gloomy, and bare, presenting the aspect of rugged desolation. 

 But in the little valleys and along the margins of the streams the vegeta- 

 tion is quite luxuriant, and the flowers are varied and abundant, render- 

 ing traveling among these wild and apparently inaccessible hills charm- 

 ing beyond description. The soil is, of course, made up of portions worn 

 away from all the different kinds of rocks in the vicinity, both the igne- 

 ous and sedimentary. Thus a remarkably rich soil is produced, which, 

 during the short season of midsummer, clothes these valleys with a 

 vegetation of bright-green, and flowers of all hues. This little lake, as 

 well as the stream that flows into it, is full of trout. The water is very 

 clear and pure, always cool, fed as it is by the melting of the snows from 

 the surrounding mountains. 



Without entering into farther details of the geology of this range, I 

 might say that there is no regular inclination to the sedimentary rocks 

 of those ranges that have been so much influenced by igneous action. 

 We find at one point the Carboniferous limestones on the east side of a 

 deep ravine, extending down the sides of the mountain like the steep 

 roof of a house, while on the opposite side the same rocks have been 

 lifted up a thousand feet or more, the upturned edges indicating by their 

 appearance that the period of the uplift was a modern event. It is my 

 belief that the principal portion of this volcanic action occurred just 

 prior to the present i)eriod, when the sedimentary and granitoid rocks 

 had been elevated somewhat as we find them at present, and that the 

 chaos which we everywhere see was produced by this general effusion 

 of igneous material, thus tossing the strata in every direction, 



A considerable amount of erosion may have occurred since, but most 

 of it had already been performed. The Carboniferous rocks, up to the 

 Tertiary Coal Series, inclusive, were in the same fragmentary condition 

 in which we find them now. 



