108 METHOD OF COMPILING THE MAP. 
Stevens. Lieutenant Abbot’s observations place Mount Adams in latitude 46° 12’, longitude 
121° 19’, (being 2’ south and 15’ west of its position on Captain McClellan’s map ;) Mount St. 
Helen’s in latitude 46° 112’, and longitude 122° 5’, (being 10’ south and 4’ west of Captain 
McClellan’s determination.) Both Wilkes and Frémont confounded these peaks. A note on 
Lieutenant Abbot’s Oregon map shows that, by his compass bearings, Captain McClellan placed 
Mount Rainier about 15’ too far east, Capt. M. placing it in longitude 121° 25’, and Nachess 
Pass in longitude 121° 25’. 
Lieutenant Arnold’s survey, in 1854, through the Nachess Pass, after correcting his longi- 
tude of Walla-Walla, (which he took at 118° 55’, or 8’ too far west,) places the summit of the 
Nachess Pass in longitude 121° 09’; Mount Rainier he puts in longitude 121° 25’, probably 
taking it from Captain McClellan. Lieutenant Arnold’s position of the Nachess Pass is some 
6’ north of that on Captain McClellan’s map, and differs also in being 16’ in longitude to the 
east. To represent Lieutenant Arnold’s survey would require much of Captain McClellan’s 
work to be changed; but as the latter had already been engraved before the former was received, 
it was not possible to make the change for the first edition of the general map. The additional 
examinations now being made in this neighborhood will require much of the Cascade range of 
mountains in Washington Territory to be re-engraved. 
The numerous small reconnaissances not mentioned in this explanation of the manner of com- 
piling the general map, have all been reduced to it according to the geographical positions 
determined by the other reconnaissances and surveys, the compilation of which I have dis- 
cussed. 
I conclude this chapter by giving a list of the principal points of the jaie with their 
longitudes, according to the best determinations and comparisons. 
