GEOLOGICAL SURVEY OF THE TERRITORIES. 59 



obtained. Thick beds of limestone were entirely composed of an aggre- 

 gate of these fossils. Most of them were in an excellent state of pres- 

 ervation. The lower beds donbtless belong to the Potsdam epoch. It 

 is barely possible that some other divisions of the Silurian occur 

 between the Potsdam group and the Carboniferous, but as yet we have 

 no evidence, and utitii it is discovered we will take it for granted that 

 the Carboniferous limestones and the Silurian beds are in apposition, 

 and that they all rest on the metamorphic rocks. The limestones seem 

 to dip beneath the basin on the south side of the range, and as we 

 ascend the. high and almost vertical sides of the mountain, we pass ridge 

 after ridge of limestone, each inclining at a greater angle, until, on the 

 summit, they are vertical and stand up in lofty massive walls. Thus 

 exposed for ages to the elements, they have been weathered into the 

 greatest variety of columns and other picturesque forms. Between 

 these ridges are beautiful grassy valleys, 2,000 and 3,000 feet above the 

 river, to which the mountain sheep seem to delight to descend from the 

 rocky pinnacles to graze. 



Xear the head of the Gallatin there is a very prominent cone-shaped 

 mountain, to which Captain Eaynolds gave the name of Mount Gallatin 

 twelve years ago. It is visible from a great distance on either side, 

 probably lor a radius of fifty miles. On each side of this peak, and in 

 close proximity, are two smaller i^eaks of nearly the same height. Mount 

 Gallatni is about 10,000 feet high, while the smaller peaks are about 

 9,000 and 9,500 feet. These peaks are composed mostly of limestones, 

 and the intermediate space to the cafion of the Madison, a distance of 

 thirty miles, is occupied to a great extent with these rocks. I have no 

 doubt that in the divide between the Gallatin and the East Fork some of 

 the more modern beds occur. Dr. Peale found the Jurassic beds at one 

 locality on the East Fork rising up from beneath the limestones. It is 

 probable that here there has been an inversion of the strata, as we find to 

 occur, in a marked manner, only a few miles below. Basaltic rocks are 

 found to a greater or less extent everywhere among the limestones, some- 

 times at the base of the mountains, and again at the summits or high up 

 on the sides. The igneous material seems to have issued forth from fis- 

 sures whenever a favorable opportunity presented itself. The gorges 

 are quite remarkable. In some places the waters seem to have gouged 

 out, as it were, a semicircular mass, with a vertical descent of 1,200 to 

 1,500 feet, and on the sides the massive strata of limestone are worn 

 into columns or pinnacles, so unsteady in their position that the loose 

 rocks may be pushed over into the gorge below. The bottom of the 

 caiion is full of debris, and doubtless ice had much to do in wearing 

 these very curious and immense gorges into the mountain-side. What 

 may be called the secondary series.of hills or ridges are 2,000 to 2,500 

 feet above the Madison, while the higher peaks rise 3,000 to 3,500 feet, 

 and here and there a peak sends its sharp summit 4,000 feet or more. 

 The proofs of erosion are everywhere on the most gigantic scale. The 

 caiion has been worn out in the same manner as those on the Yellow- 

 stone, but in the mean time the narrow channel doubtless became gorged 

 from time to time. The basin which we have attempted to describe, 

 which is about thirty miles in length and ten to fifteen in breadth, was 

 once a fresh-water lake, but the water slowly wrought its way through 

 this high range of mountains. Near the immediate entrance of the 

 caiion, on the east side of the river, there is a short, high, terrace-like 

 ridge, about one-fourth of a mile long, 250 feet high above the bed of the 

 river, paved on the surface with rounded bowlders, and, I have no doubt, 

 made up of a local drift. The upper end is quite abruj)t, steep, and at 



