2 
DETERMINATION OF THE PROFILES.—GEOLOGY. 
accuracy. I have also, in the preparation of the maps, used some determinations of latitude 
and longitude made by the boundary commission and by Colonel J. E. Johnson, of the topo¬ 
graphical engineers. 
For tracing the line of survey over the short distances between the astronomical positions, 
the compass fixed in position was used, and the lengths of the compass courses measured with 
a viameter, which had been carefully compared with the measurements by the chain. As all 
error in measurement or hearing was confined to the short distances between the fixed points, 
the details of the route may, I think, he considered sufficiently accurate. 
All the astronomical observations, with the results of the computations in each case, are 
appended to this report. The instruments used were—sextant, eight inches diameter, by 
G-ambey, Paris ; chronometer No. —, by Parkinson & Frodsham. 
Determination of the profiles .—The profiles of the route, and of the experimental lines on 
each side of it, were determined by a continuous series of angles of elevation and depression, 
observed with a theodolite. This method is unusual in the survey of lines so extended, and is 
a much more detailed and tedious process than that usually adopted. 
Although liable to errors in the determination of absolute altitudes above the sea-level, this 
method is probably more accurate than that by the barometer for determining the relative 
heights of points not remote from each other; and covering, as it does, every foot of the route, 
it exhibits every feature of the country and every undulation of its surface with a detail abso¬ 
lutely unknown to any process other than that of the level. 
The results, which have been compared at a few particular points with barometric determi¬ 
nations, exhibit an approximation sufficiently close to he convincing of their general accuracy. 
With this duty, in connexion with the compass courses of the route, and of the prominent 
features of the country contiguous to it, I charged Lieutenant Garrard, 1st dragoons, my prin¬ 
cipal assistant, and he executed it with a zeal and ability worthy of every commendation. A 
table of the observations, with the deduced results, is appended. The instruments used were— 
theodolite, made by W. & E. Jones, London; odometer, for measurement of distances. 
The following maps accompany the report, viz: 
1st. A general map on a scale of ten miles to one inch, or g-g-gg^, exhibiting the route sur¬ 
veyed, and the country contiguous to it. The lower side of the map is faced with a profile of 
the route from El Paso to Preston, on the Bed river. On the left side will he found a short 
profile from Dona Ana to the Hueco Tanks; and on the right, a profile from the emigrant 
crossing of the Pecos to the Big springs of the Colorado. These profiles are made upon the 
same longitudinal scale as the map, with a vertical scale of 2,000 feet to the inch, or As 
the line of survey has nearly an east and west direction, the prominent places on the map will 
he found to he nearly above corresponding points on the section, which can thus he easily 
referred to for the altitude and grades. 
Map No. 2. A map and profile of the Guadalupe Pass, on a scale of 5,000 feet to the inch, 
or gg£g(j; vertical scale of profile, g^Vir- 
Map No. 3. Map and profile of the pass through the Hueco mountains, on a scale of 5,000 
feet to the inch, or 0 ; vertical scale of profile, g^Vv 
Geology and geological profile of the route .—It was impossible to secure the services of a geolo¬ 
gist to accompany the party; and it became necessary, therefore, to adopt some method for 
collecting specimens in this department of science, which would enable a skilful geologist, who 
had not been over the country, to arrive at a sufficient knowledge of its geological structure. 
The plan determined upon was in every respect satisfactory, as will he seen from the geological 
report. Specimens were collected from the strata of the ridges and mountain-ranges, from all 
outcrops, and from the surface of the ground and beds of streams, and were labelled as follows: 
first, locality; second, distance from summit; third, position of the stratum from which it was 
taken relatively to the others, and its inclination to the horizon. Many specimens of minerals 
