251 Geology and Botany of Northern Pacific Railroad. 



ing. A branch of the N. P. R. 11. runs up to Wickes, carrying 

 coke and other supplies at so cheap a rate as to give success to 

 enterprises which were before unprofitable. The ores worked 

 are argentiferous galena, containing much blende and pyrites. 



The limestone series in this valley is underlain by heavy beds 

 of quartzite, which apparently represent the Potsdam sand- 

 stone. 



Red Mountain, sixteen miles west of Helena, lies at the head 

 of another valley similar to that at Wickes ; but the quartzites 

 are here less conspicuous ; the limestones only becoming silicious 

 and flinty at their base. Red Mountain is cut by an immense 

 number of mineral veins, generally of small size, from one to 

 six feet in thickness, but exhibiting a remarkable uniformity 

 in direction and mineral characters. They are approximately 

 parallel, apparently continuous through the mountain, stand 

 nearly vertical, and carry argentiferous galena, gray copper, 

 zinc-blende and pyrites. The veinstone is chiefly quartz, but in 

 some places consists almost entirely of black hornblende. The 

 ores generally carry from 25 to 100 ounces of silver, but the 

 gray copper, which is the richest, contains from 200 to 2,000 

 ounces per ton. Systematic mining operations are just begin- 

 ning here ; and should a branch road be carried up to the 

 mines, it would seem that they must be productive and pro- 

 fitable. 



After passing Helena, the line of the Pacific Railroad soon 

 turns into the mountains and crosses the first or main range, 

 coming down on to the head waters of Clark's Fork and enter- 

 ing a broad and fertile valley, which has its chief center of 

 population at Missoula. The western border of this valley is 

 formed by the Bitter Root Mountains, part of the broad belt 

 made up of the western ranges of the Rocky Mountain system. 

 All these consist of granite, broken through in many places by 

 eruptive rocks, and flanked by quartzites, slates and limestones, 

 which probably represent the Cambrian, Silurian and Carboni- 

 ferous systems. In the lowlands which lie between the ranges, 

 there are basins of quite modern Tertiary rocks. 



A few miles below Missoula the road crosses a series of 

 deep ravines, spanned by bridges, one of which is 211 feet in 

 height. The rock exposed here is all slate of Archaean or Cam- 



