METHOD OF COMPILING THE MAP. l 95 
map was compiled and engraved in 1854, since which time several good determinations of 
longitude have been obtained, and compare as follows with those upon this compilation: 
Point Seul Choix, 85° 48’, general map; 85° 50’, Captain J. N. Macomb, T. E.* 
Chicago, 87° 40, general map; 87° 38', Major J. D. Graham, T. E.t 
Lyons, Illinois, 90° 14’, general map; 90° 14’, Major J. D. Graham, T. ۳. 
West Bound. Missouri, 94° 38’, general map; 94° 40’, J. H. Clark.$ 
The land surveys have been reduced on the bases thus established as far east as the map 
extends, and as far west as these surveys have been made. 
These surveyed lands are bounded on the west by an irregular line extending from the 
Upper Mississippi, southwest by the St. Peter's river, across the northwest corner of Iowa to 
the Big Sioux river, and thence south, through the eastern parts of Nebraska and Kansas, 
(passing near the mouth of Loup Fork and Fort Riley,) and thence along the west boundaries of 
Missouri, Arkansas, and Louisiana, to the Gulf of Mexico. These surveys, therefore, deter- 
mine the geographical position of the eastern portion of most of the lines of exploration with 
much more precision than the few hasty and imperfect astronomical observations which the 
parties were enabled to make. This method of reducing the land office surveys has also located 
the Mississippi river with a geographical accuracy probably not before equalled by any map. 
The land surveys in Utah furnish us with a map of a considerable area along the western 
foot of the Wasatch mountains near the Great Salt Lake, their geographical position being 
determined by the results of Captain Frémont's astronomical observations near the site of 
Great Salt Lake city in 1845. 
The land surveys in New Mexico are as ye confined mainly to the valley of the Rio Grande, 
but in the latitude of Santa Fé, have been extended east to the sources of the Canadian river. 
These surveys connect the Mexican boundary surveys with those near the 35th parallel. 
The land surveys of California, Oregon, and Washington Territories, also afford much relia- 
ble information. The “San Bernardino meridian” passes through the summit of the peak of 
that name, in the southern part of the State of California, and, as referred to the astronomical 
determinations of the United States Coast Survey, is in about longitude 116° 55'. "The Monte 
— passes through the summit of Monte Diabolo, about twenty-seven miles east 
isco m in = Bh, ana کا‎ by the Coast sate determinations, oe 123° a 
Roc ne 
tude of Fort panty at about 122° 1l'09". At the time of constructing this RAS of the 
general map, the best determination of this point which we possessed was that of Captain J. 
C. Frémont, published in his Geographical Memoir of Oregon and Upper California. This 
places it in longitude 122° 6' 50". The determinations of Lieutenants Williamson and Abbot 
place it in longitude 122? 10’ 50”, closely agreeing with the Land Office work referred to the 
Coast Survey. 
In Oregon and Washington Territories, the principal meridian of the Land Office surveys 
passes through the point of land formed by the junction of the Willamette and Columbia rivers. 
Its longitude has been determined by measurement between it and several points of the United 
® See charts of lake surveys under Topographical Bureau. | 
+ Obtained by magnetic signals between Chicago and Quebec. 
f Chronometer difference between Lyons and Chicago.—(See proceedings Chicago Historical Society, 1858.) 
$ Survey of southern boundary of Kansas in 1858 
