LETTER OF TRANSMITTAL.

DEPARTMENT OF THE INTERIOR,

UNITED STATES GEOLOGICAL SURVEY,

Washington, D. C., February 21, 1900.

SIR: I have the honor to transmit herewith a detailed report relating to the survey of the boundary line between Idaho and Montana from the international boundary to the crest of the Bitterroot Mountains.

I wish to make acknowledgment of the valuable services rendered in this connection by Messrs. S. S. Gannett and D. L. Reaburn, in field and office, and by Mr. E. T. Perkins, jr., in the field. Mr. Gannett prepared the greater portion of the material relating to latitude, longitude, base line, azimuth, and triangulation.

SURVEY OF THE BOUNDARY LINE BETWEEN IDAHO AND MONTANA FROM THE INTERNATIONAL BOUNDARY TO THE CREST OF THE BITTERROOT MOUNTAINS.

By RICHARD U. GOODE.

INSTRUCTIONS.

The survey of the boundary line between Idaho and Montana was provided for by the Fifty-fourth Congress in the sundry civil act approved June 4, 1897.

The following correspondence is self-explanatory:

DEPARTMENT OF THE INTERIOR,
UNITED STATES GEOLOGICAL SURVEY,

Washington, D. C., June 5, 1897.

The honorable the SECRETARY OF THE INTERIOR.

SIR: In response to your verbal request, I have the honor to transmit herewith suggested instructions relating to the survey of the boundary line between Idaho and Montana.

I am, with respect, your obedient servant,

CHAS. D. WALCOTT, Director.

INSTRUCTIONS RELATING TO THE SURVEY OF THE BOUNDARY LINE BETWEEN IDAHO AND MONTANA.

Included in the act making appropriations for sundry civil expenses of the Government for the fiscal year ending June 30, 1898, and for other purposes, is found the following law:

For surveying that portion of the boundary line between Idaho and Montana beginning at the intersection of the thirty-ninth meridian with a boundary line between the United States and the British possessions, including the retracing of so much of the international boundary line as may be found necessary for the determination of said intersection, then following said meridian south until it reaches the summit of the Bitterroot Mountains, and for locating points on said meridian by triangulation from the Spokane base of the United States Geological Survey, and on the continuation of said boundary line along the Bitterroot Mountains between Idaho and Montana, seven thousand six hundred and fifty dollars, or so much thereof as may be necessary, to be immediately available: Provided, That the Secretary of the Interior shall direct that the survey shall be executed under the supervision of the Director of the Geological Survey by such persons as may be employed by or under him for that purpose, and such survey shall be executed under instructions to be issued by the Secretary of the Interior: Provided further, That the plats and field notes thereof prepared shall be approved and

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certified to by the Director of the Geological Survey, and three copies thereof shall be returned, one for filing in the surveyor-general's office of Idaho, one in the surveyor-general's office of Montana, and the original in the General Land Office. In carrying out the provisions of the law above quoted three special processes are involved:

First. The accurate location of the thirty-ninth meridian on the ground by triangulation from the Spokane base of the United States Geological Survey, including the retracing of so much of the international boundary line as may be found necessary for the determination of the intersection of the thirty-ninth meridian with the said boundary line, as well as for locating points on the continuation of the boundary between Montana and Idaho along the summit of the Bitterroot Mountains.

Second. The marking on the surface of the ground, by proper monuments, of the boundary as determined.

Third. The preparation of the necessary plats and field notes.

With reference to the above, the following instructions will be observed:

LOCATING THE BOUNDARY.

The Spokane base of the United States Geological Survey is referred to the meridian of Greenwich, and the thirty-ninth meridian above mentioned has for its initial point the meridian of the old Naval Observatory at Washington. By applying the proper correction and referring the thirty-ninth meridian west of Washington to the meridian of Greenwich, the result is that the meridian to be determined as the boundary line between Idaho and Montana is 116° 03′ 02′′.30 west of Greenwich.

The triangulation from the Spokane base will be extended eastward so as to accurately locate the intersection of the meridian above mentioned west from Greenwich with the summit of the Bitterroot Mountains. It may be that this identical point can not be located directly by triangulation, but a point as near thereto as may be possible should be so located, and from this the exact point should be determined by careful traverse based on an astronomic or calculated azimuth and distances determined by direct chaining or stadia measurement, whichever may be most practicable.

After the point referred to, namely, the intersection of the meridian 116° 03′ 02′′.30 west from Greenwich with the summit of the Bitterroot Mountains, has been determined, the triangulation is to be extended northward, locating as many points as may be practicable as near as may be to the boundary line between Idaho and Montana until the international boundary is reached. From the points so located by triangulation other points exactly on the boundary will be determined by traverse in the manner hitherto mentioned. The international boundary line is supposedly on the forty-ninth parallel of latitude. It will not, however, answer the purpose to rely on the location of this parallel from the Spokane base, but it must be determined with reference to an existing monument or monuments, being carefully retraced until its point of intersection with the meridian is exactly located.

The distance along the international boundary from the nearest monument, or the monument recovered, to the point of intersection will be determined either by triangulation or direct measurement with chain or stadia or a combination of the two methods.

After points as above described have been located on the boundary line between Idaho and Montana from the international boundary to the summit of the Bitterroot Mountains, these points will be joined by true meridian lines, so that a sufficient number of points on the boundary in addition may be determined to fulfill the conditions made necessary under the provisions hereinafter mentioned for mark