ROUTE FROM FORT BENTON TO WALLAH-WALLAH. 271 
enable me to speak positively concerning the curves. The deflection from the direct line, con- 
necting the crossing of the Teton with the pass, would be inconsiderable, and by curves, accord- 
ing to my estimate, of from two to six thousand feet radius at the crossings ; to avoid the uneven 
ground between the Sun and Dearborn rivers, and in the vicinity of the pass, curves adopted to 
secure the proper gradients. Without being certain of the point, I think it would be safe to 
estimate that the tunnel would have to be cut through a formation of which fifty per cent. is a 
rock of clay slate. 
Our observations show that the Blackfoot fork, down which we travelled, descends at the 
rate of thirty feet per mile. Making a due allowance for errors, I estimate that the railroad could 
descend for the first thirty-six miles with a gradient of forty-five feet per mile, and for the remain- 
ing distance, to the valley of the Bitter Root, with one of thirty-five feet per mile. In the last ten 
miles of the thirty-six, four sharp curves would be necessary; but the location could be so made 
that neither would require to have aless radius than two thousand feet. At our camp of the 24th 
and 25th of September the valley of the Blackfoot fork becomes enlarged, the mountain spurs 
receding off either side to a distance of six or seven miles from the stream; the intermediate space 
has a gentle slope connecting the bases of the mountains with the stream. Mr. Tinkham reports 
that this valley could be favorably connected with the summit between it and the tributaries of 
the Flathead river. I think that further examinations might establish a very good connexion by 
this route with the valley of Clark’s fork. For a line down the Blackfoot fork, there would occur 
two curves of the minimum radius before reaching the valley of the Bitter Root. The last 
twenty miles are through a defile, where there would be about twenty-five per cent. of rock- 
cutting; the rock being a kind of limestone, which appeared to disintegrate rapidly by exposure 
to the weather. 
In the event of Mr. Lander’s report being adverse to the practicability of the line of the Bitter 
Root river, it seems to me that, with our present knowledge, the following is the best plan for 
making the descent into the valley of Clark’s fork of the Columbia: Leave Hell Gate river at 
the mouth of the Blackfoot fork, and pursuing the hill-sides and the plateau which intervene, 
attain the summit of the first hill occurring between the Bitter Root and the Jocko, This, as our 
observations indicate, could be accomplished with a gradient of thirty-five feet per mile :.to allow 
for errors, I estimate it at forty feet per mile. Having attained the summit, strike a tributary of 
the Jocko, which is adjacent to the present trail, and descend along its banks and those of the 
Jocko to the valley of the Flathead, and so to that of Clark’s fork; which name I here propose to 
apply to the stream below the junction of the Bitter Root. The descent to the valley of the 
Jocko could be made with a gradient of forty feet; this grade is assumed at fifty feet. Hence, 
to the junction of the Bitter Root with the Flathead, it would be one of twenty feet. Another 
plan for passing from the Blackfoot to Clark’s fork has been already alluded to. It is that which 
is referred to by Mr. Tinkham. If it should prove to be as favorable throughout as is supposed, 
it would be by far the preferable plan. 
The means of our observations indicate that the average fall of Clark’s fork is about eleven 
feet per mile. I estimate that the railroad could descend with gradients of from fifteen to twenty 
feet per mile. As far as I can at present say concerning the location, I think the road, after 
passing from the valley of the Jocko into that of the Flathead, would follow the hills on the lett 
of the stream to a point some miles above its junction with the Bitter Root. Then crossing the 
former, it would follow the right banks of Clark’s fork as far as Big Rock; here it would cross, 
and, following down the left bank, would recross at the Cabinet. Then tunnelling the Cabinet 
mountains three hundred yards, it would continue on the right of the river to Lake Pend d’Oreille, 
and on the eastern side of that to its lower extremity. 
As the lake is subject to high freshets, perhaps variations of fifteen feet from low to high water, 
it would be necessary to run the railroad above this, by keeping the sides of the hills, and in some 
