METHOD OF COMPILING THE MAP. 105 
The Kansas river, as far west as Fort Riley, has been reduced from the Land Office surveys. 
Captain Gunnison’s survey for a railroad route has, therefore, not been used east of that point. 
His map, as constructed by Mr. Egloffstein, places Fort Riley in longitude 96° 50’, being 6’ 
too far west, and of the mouth of Walnut creek 98° 49’, instead of 98° 42’. The work between 
these two points has been moved 6 to the west. From Walnut creek to Choteau island 
Brown’s survey was used in the compilation, and from that point (which coincides in position 
with that from Captain Gunnison’s survey) westward, the maps prepared by Mr. Egloffstein 
from Captains Gunnison and Beckwith’s surveys, have been exactly copied, except for the 
position of Fort Reading, which was assumed by Mr. Egloffstein as 1’ 42" eastward of Colonel 
Frémont’s location, or about 6’ too far east. This error in Captain Beckwith’s map was 
distributed through his work in the Sierra Nevada. 
Captain Stansbury’s routes have all been copied on our map nearly as given by him west of 
the meridian of Fort Laramie, subject only to such slight changes as Captain Beckwith’s and 
Lieutenant Bryan’s surveys showed to be necessary. He, however, adopted from Mr. Nicollet 
the longitude of Fort Leavenworth, (94° 45’,) instead of 94° 58’, which required his route to 
be shortened 13’ between this fort and Fort Laramie. Fort Kearny had thus to be moved 
8’ west of its position on Captain Stansbury’s map, that is, from 98° 58’ to 99° 06’. The 
chain and compass survey made between Fort Kearny and Omaha by Captain Dickerson, in 
1856, showed the difference of longitude between them to be very nearly the same as I had 
adopted, the longitude of Omaha being determined by the Land Office surveys, as before 
explained.* Lieutenant Bryan, on his map of explorations to Bridger’s Pass, adopted the 
position of Fort Kearny as given by Captain Stansbury, although he changed Fort Leaven- 
worth, upon which Captain Stansbury’s determination depended by his compass survey, no 
astronomical observations having been made for its longitude. The longitude of the mouth of 
the Platte being determined from the Land Office surveys, this stream has been laid down from 
Colonel Frémont’s and Captain Stansbury’s maps to conform to the longitudes of the points I 
have enumerated. 
The mouth of the Big Sioux, according to the Land Office surveys, referred to the meridians 
determined s as s already described, is about 12’ west of what it is as given by Mr. Nicollet. The 
io Lake Jessie, according to Governor Stevens’ map, is also 12’ west of Mr. Nicollet's 
ote - ination 2 ed Mr. Nicollet's work is uniformly from 19 to 15' too far east along the 
wher ked, I have thought it best to move it entire from the mouth of the 
Big Sioux to Fort feu and thence to Devil's lake, 12’ to the west; Fort Pierre then becomes 
in longitude 100° 243’, instead of 100° 1284. — 
The longitude of the mouth of the St. Peter’s river having been adopted from Mr. Nicollet, 
and the route to Devil’s lake having been moved 12’ west, Mr. Nicollet’s routes between 
the meridians through these points have so been put down as to proportion this difference 
throughout. 
In my map of ‘‘ Reconnaissance in the Dacota country," I assumed the positions adopted on 
the general map. In my explorations on the Missouri and Yellowstone, in 1856, I determined 
the longitude of Fort Union, by two sets of moon culminating stars, to be 1049 02' 077", cor- 
responding nearly with that adopted by Governor Stevens. The Missouri river has been put 
? The difference of longitude between Fort Kearny and Nebraska city, by the Land Office surveys made in 1858, confirms 
the position I have adopted. 
14 
