338 REPORT AND ESTIMATE. 
twenty-one hundredths, four and sixty-four hundredths, thirty and nine-tenths, five and thirty- 
five hundredths thirteen and one-tenth, thirty and nine-tenths, forty-five and six-tenths feet 
to the mile. At the great falls of the Missouri, where in fifteen miles there is a fall of 
357 feet, the grades must be adjusted with great care at the expense of heavy work. 
For ten miles above the forks of Sun river the grades will vary from forty to fifty feet per mile. 
The work of excavation and embankment will be light. Thence to the tunnel of Lewis and 
Clark’s Pass is nineteen and one hundred and twenty-one thousandths (19.121) miles, all very 
difficult and heavy work. The tunnel itself is two and one hundred and twenty-nine thou- 
sandths (2.129) miles in length. The summit level of the tunnel із at a debouche a half mile west 
of the western base of the mountain, and is 5,698.6 feet above the level of the sea. It passes 
out on a descending grade of sixty feet to the mile, at an elevation of 5,570.86 feet above the 
sea, the summit level of the mountain being 6,519.3 feet above the sea. Asin Cadotte’s Pass, 
the eastern approach is by a ravine north of the travelled trail. In ten miles above the forks 
the line leaves the general valley of the Elk Fork, crossing the highest summit about halfway 
between the route of the party of 1855 and Heart mountain, and crosses Dearborn river at an 
elevation of 4,994 feet above the sea, and about one mile above the trail. The country is lower 
and less broken by this route than in any other part of the plateau between the upper waters 
of the Sun and Dearborn rivers. The Dearborn itself leaves the mountains by a gap in a direc- 
tion nearly east, when it turns suddenly to the south, and continuing on three miles, it turns 
suddenly again to the east to the point where it crosses the trail. The railroad line follows along 
the Dearborn on this south line three miles, and makes the crossing just below its last turn to the 
east. A bridge, one mile in length and nearly 300 feet above the valley, which at this point 
has an elevation of about 4,700 feet above the sea, will be required to cross the Dearborn. 
Thence for two miles and three-eighths the road will follow very nearly the natural grade, vary- 
ing from forty to sixty feet to the mile. In two miles and three-quarters further we come to a 
ravine, in which flows a stream of water which can only be turned by continuing up the ravine 
and keeping closely along the side hills. Between this point and the entrance to the tunnel, a 
distance of 43 miles, there will be seven small streams to cross, involving the adjustment of a 
grade of sixty feet to the mile, the necessity of constant curvatures with radii of 1,500 
or 2,000 feet. There will be very heavy embankments required to cross these several 
streams, which can, however, be made up from the adjacent spurs with hauls exceeding in no 
case a half mile. Moreover, the ravine, into which the tunnel debouches on the east, by the 
best system of side-hill approach, must be filled up, which can be done by the debris from the 
tunnel. The country at right angles to the line of the road rises towards the mountains at a 
grade of from one-fourth to one-eighth. This is equally the case with the ravines in which the 
streams flow and the intermediate divides. Debouching from the tunnel on the western side, 
the line continues in the valley of the stream for five miles at a grade of thirty-five feet, with 
an excavation and embankment almost entirely along the natural surface; and for a mile and a 
half further at a grade of forty-four feet to the mile, when we leave the stream, and, making a 
cut through a low divide of about 700 feet in length, come upon a gently sloping prairie, down 
which it can be laid and brought into the valley of the Big Blackfoot through the open valley 
of a small stream at a grade of from sixty to sixty-five feet tothe mile. This grade will involve 
closely hugging the side hills which line the valley of the small stream and the Big Blackfoot 
on the west, and will involve a curve of the minimum radius. The greatest depth of the cut 
will be 134.7 feet. For the first 80 feet the cut will be from 134.7 feet to 122.6 feet in depth, 
