42 THE UNITED STATES GEOLOGICAL SURVEY. |bull.227. 
notebook, the contours and stream courses are roughly sketched, 
and the whole serves as a basis for the geologic notes. The work is 
checked with that of the topographer or, in the absence of a topog- 
rapher, with the known positions of terminal points. 
All possible information is obtained in regard to bed rock, with 
special reference to the occurrence of mineral deposits, and specimens 
are collected for future study. In the trips of a reconnaissance char- 
acter more attention is given to the stream gravels, perhaps, than when 
time is less pressing. These local collections often throw light on the 
qualitative lithology of an area, while the quantitative character has 
to be left largely undetermined. The geologists are also called upon to 
make notes on the distribution of timber, fish, and game, and to gather 
information about the natives as well as the white population. A 
number of the expeditions have made valuable collections of plants. 
In making topographic maps of the different parts of Alaska, it has 
been found necessary to adopt special instruments and methods fitted 
to the exceptional conditions encountered, though the general scheme 
for executing topographic work is the same as elsewhere. 
In reconnaissance surveys the work is started, if possible, at some 
place of known position; otherwise observations are made with a 
transit having a vertical circle to determine the latitude and azimuth 
at the starting point, and longitude is determined by tying the traverse 
to some point previously established. Starting from the point thus 
ascertained, angles are taken and distances measured along the trav- 
erse, and these are plotted on a plane-table sheet to the scale of about 
3 miles to the inch. Distances are determined by stadia measurements 
with a telescopic alidade or a hand stenometer, both of these instru- 
ments being devised for use with a short base or with a rod of known 
length. When atmospheric conditions prevent the use of paper for 
plotting the traverse, a sheet of white celluloid is substituted. 
As the traverse progresses salient features of topography are located 
by intersection, and the elevations of these points, as well as of stations 
actually occupied, are determined by vertical angles or barometric 
readings. These locations enable the topographer to adjust his sketch 
showing the drainage and configuration of the country adjacent to the 
route. As often as possible latitude and azimuth observations are 
made and sights to prominent mountains are taken, thus enabling a 
more accurate adjustment of the field sheets. 
In localities where large areas have been mapped, such as Seward 
Peninsula or the Copper River Basin, the method is that usually 
employed by the Survey in other fields. A base is laid out and triangu- 
lation is expanded instrumentally until a sufficient number of points 
are located to control the area to be surveyed. The positions of these 
points are computed and plotted on a plane-table sheet, to serve as a 
control for intervening locations, which are filled in by graphic triangu- 
