REMARKS ON THE MAP AND SECTION. 
THE MAP. 
The Geological Map accompanying this report exhibits the line of the survey, with the camps, 
from Fort Smith to the Pacific. It also includes the valley of the Arkansas clown to its inter¬ 
section with the Mississippi river. The scale adopted is the same as that of the General Map 
of the Territories now being compiled and engraved in the office of the surveys. This scale is 
1 : 3,000,000, or about forty-seven miles to one inch. The whole line is thus brought into a 
small compass, and can he easily referred to when consulting the report. Its width being less 
than the length of the quarto page, does not require it to he folded in more than one direction 
when placed in the report. The trail is indicated by a broken line, and the principal camps by 
numbers ; the intermediate camps being indicated, but not numbered. 
The mountains are not shown by the ordinary shading used in maps, but by broken and 
slightly overlapping black lines, which are placed in the direction of the trends of the ranges. 
These lines, with the coloring used for the granitic rocks of which the ranges are nearly all 
composed, sufficiently indicate their position on the map. The scale is so small that some of 
the minor details of the boundaries of the different formations were necessarily sacrificed, and 
it was not possible to represent some of tbe dykes of trap by colors, of the size required by con¬ 
formity to the scale. The outlines or boundaries of the formations are shown by a fine dotted 
line; and, except in a few instances, the attempt to show their extension far beyond the line of 
exploration has not been made. 
GEOLOGICAL SECTION. 
The Geological Section which accompanies this report is designed to give an approximate 
representation of the chief features in the geology of the country, on and near the line of 
Lieutenant Whipple’s survey. This line, as is known, extends from the Mississippi river west¬ 
ward to the Pacific ocean, at San Pedro, and for the greater part of its course is in the vicinity 
of the 35th parallel of north latitude. The line of the section does not, however, follow the 
line of the survey throughout its whole course, but has been modified so as to respresent, as 
nearly as possible, the configuration of the region on a direct line, avoiding the detours to the 
north and south unavoidable in the operations of the survey. The barometrical and viameter 
measurements of Lieutenant Whipple have served as the basis for the section, and the height and 
distances where the two lines correspond have been taken from them. The scale adopted for 
these representations on the section is two miles to one inch, or half an inch to one mile ; the 
scale for vertical and horizontal distance being equal. The profile of the section consequently 
shows, as nearly as possible, the slopes and grades with their natural inclination, and, indeed, 
is intended to be a truthful miniature representation of the relief of the country. 
The belt of country represented extends over twenty-eight degrees of longitude, or about 
1,590 miles from east to west. The whole distance along the circuitous line of the survey is 
2,0T5 miles ; but the section is shortened and made more direct in its course, so that it repre- 
