18 SURVEY OF IDAHO-MONTANA BOUNDARY LINE. [bull. 170. 
the purpose. In fact, the appropriation made would not -have been 
adequate for the work that was accomplished if it had not been pos- 
sible to utilize, in connection with the boundary line, work done 
under other appropriations. In this manner about 50 miles of the 
boundary were accurately located in connection with the survey of 
the Hamilton quadrangle, a portion of which is embraced within the 
limits of the Bitterroot Forest Reserve. 
The crest line of the Rocky and Bitterroot mountains between Idaho 
and Montana is generally a clearly defined summit or watershed, so 
that no serious question need arise as to its identification as an inter- 
State boundary. (See PI. I.) In a few localities, notably in some of 
the passes, there are morasses of small extent out of which the water 
flows or seeps in both directions. If the question of placing monu- 
ments to mark this line ever arose, the location of monuments in 
such swampy localities as are found to exist would probably fulfill 
all necessary requirements. It is, however, very desirable that topo- 
graphic maps of the adjacent territory be prepared. Such maps would 
clearly differentiate the true summits from the diverging spurs, and 
prevent any possible misconception as to the location of the line. 
After these maps had been prepared there would be no further ques- 
tion of surveying, but merely one of placing monuments, should this 
be considered necessary. 
It frequently happens, as the result of greater or less relative ero- 
sion or uplifting, that spurs have an elevation higher than that of the 
main watershed, and this is remarkably the case in certain portions 
of the Bitterroot Mountains. In fact, in those portions where detailed 
examinations have been made all of the higher points of the range are 
uniformly from 6 to 8 miles east of the present divide, and it is prob- 
ably true that this divide, in the course of geologic time, has retreated 
from an irregular line which passed through these high points. This, 
if true, is due partly to the fact that the waters of the Bitterroot 
River draining to the eastward have a greater relative rate of fall, 
and consequently greater erosive power, than had the waters flowing 
westward through the Clearwater, and thus the territory tributary to 
the former is gradually being captured by and added to that of the 
latter. 
ACCOUNT OF OPERATIONS. 
The work in connection with the boundary line extended through 
portions of three field and office seasons. 
The act providing for the survey of the boundary line was approved 
June 4, 1897, and Mr. E. T. Perkins, jr., topographer, was immedi- 
ately detailed for field work in connection with the triangulation. 
Mr. Perkins left the city of Washington on June 10, and proceeded 
to Spokane, Washington, by way of Boise, Idaho, stopping at the 
latter place to arrange for the transportation of certain property to 
