O SURVEY OF THE COLORADO OF THE WEST. 
ble to make the sides of the triangles from twenty-five to thirty miles 
long, and occasionally, when the artificial points were on very salieDt 
natural points, the sides of the triangle could be made much longer. 
Six of the more distant and important geodetic points were used as 
astronomic stations, where observations were made with the zenith tel- 
escope for latitude, for the purpose of checking any serious error that 
might occur in the triangulation. 
From the points thus established a number of observations made were 
v ith the theodolite or gradientor, and from these observations a vast 
net-work of secondary triangles was constructed. Thus the position of 
all the salient topographic features were determined, courses of streams 
and lines of cliffs were meandered, and the position of the observer con- 
stantly checked on the determined points, and pari passu with this the 
topographical features were sketched. The great features were Marble 
Canon and the Grand Canon of the Colorado, and many salient points 
on either side of the great chasm were fixed by triangulation. 
The following summer we descended through these canons in boats, and 
fixed the course of the river and the topographic features of the canon 
wall by compass and gradientor observations on the points thus pre- 
viously determined. The same system of barometric observations car- 
ried on in the canons above was continued through these canons, and 
occasionally hourly observations of eight-day series were made. 
The parties engaged in geodetic and topographic work carried with 
them barometers, and made a vast number of observations over the 
country traversed. All of these and all of those in the canons were 
synchronous, with a continuous series made at the northern extremity 
of the base-line in the valley of the Ivanab, so that the altitudes along 
the river and on the walls of the canons, and over all the country em- 
braced in the tri angulation, are referable to this hypsometric base. We 
have compared this base of altitude with other points whose altitudes 
have been approximately determined by other observers, as at the 
mouth of the Eio Virgen, Saint George, Beaver, Salt Lake Gity, &c. ; 
but it is hoped that before this work goes on permanent record the alti- 
tude of Kauab above the level of the sea will also be determined by 
the levels of the railroad survey, which is now in progress. 
. We have one unbroken series of observations at this point (Kanab) 
of three months’ continuance, and another of ten months, and several 
shorter series. These were tri-daily, except that occasionally they were 
expanded into hourly series. 
By the methods last described, an area of country has been surveyed 
embracing twenty-five thousand square miles, and by the less accurate 
methods first given, an area of country embracing twenty thousand 
square miles, making in all forty-five thousand square miles. 
Preliminary maps have been constructed on a scale of two miles to 
the inch, but the final result of all this work will be shown in a series 
of maps on a scale of four miles to the inch, giving the topographic and 
geological features of the region surveyed. 
