It is by way of the Mullan Pass--so named from the fact of Lieut. John Mullan, U. S. A., having built a wagon road through it in 1867, to connect Fort Benton, Mont., with Fort Walla Walla, W. T.,--that the railroad is carried over the continental divide. The highest elevation of the pass itself is 5,855 feet; but, by the construction of a tunnel 3,850 feet in length, the line was made to reach the western slope without attaining a higher elevation than 5,547 feet. It is not until Butler is reached, thirteen miles from Helena, that either the scenery or the construction of the road calls for special notice. But at that point the scenery becomes exceedingly picturesque, the rocks towering above the pines and spruce like the ruins of some ancient stronghold. From now on, too, the tourist will find constant employment in observing how the gigantic barriers, which seem to forbid all further progress, are, one after another, overcome. Amid scenery increasing in wildness and grandeur, the train pursues its tortuous course; through Iron Ridge Tunnel, near which the track forms an almost perfect letter S; across innumerable ravines; along rocky shelves and through deep cuttings, until at last it enters the eastern portal of the Mullan Tunnel. A few minutes later the traveler is looking out upon the grassy hills and pleasant valleys of the Pacific slope, the approach to the tunnel from the west presenting a singular contrast to the savage grandeur that distinguishes the approach from the east. Following the valley of the Little Blackfoot, the train presently arrives at Garrison, where passengers desirous of visiting the most flourishing mining city on the American continent, if not in the world, must change cars. "The most flourishing mining city on the American continent, if not in the world!" exclaims the reader. Even so; and yet we are not in Nevada, nor yet in Colorado; and, besides, the former is about played out; and, as for Leadville, every one remembers the disasters that overtook her, culminating, as they did, in the failure of all her four banks. The city is Butte, that, at the last United States census, had a population of only 3,363, but now claims six times that number, and has a monthly mining pay-roll of $620,000. The line from Garrison runs through the beautiful Deer Lodge valley, in which are many fine farms. Deer Lodge City, the judicial seat of the county, is pleasantly situated 4,546 feet above sea-level. Being well laid out, it presents, with its wide streets and handsome public buildings, an exceedingly attractive appearance.