158 APPENDIX. 
staff measuring the angle between the object and the other 
staff. 
In this manner the neighbourhood of any station may be 
mapped down so as to be available for many useful purposes, 
In all such cases the compass bearings of the most impor- 
tant object in the horizon should be taken ; and in the absence 
of the sextant angles, azimuth compass readings of each 
point may be substituted, though, of course, with less 
precision. . 
Indications of the progress of the expedition should be 
left at various points in its course, by making marks on rocks, 
or stones, &c., and by burying documents in bottles. In 
regard to the latter, it will be necessary to deposit them one 
foot deep at some known distance, say fifteen feet from a con- 
spicuous surface of stone, on which there is painted a circle 
containing the distance and bearing by compass of the bottle, 
from its centre ; and that the situation of such places of de- 
posit should also be ascertained by exact compass bearings of 
several remarkable points in the herizon, both near and dis- 
tant, as wellas by angles between them, carefully determined 
with a sextant, and noted down in the journals of the expe- 
dition for their own reference, or that of future travellers. 
In surveying the basin of a river, or in proceeding along 
the prevailing slope of a country, it is very desirable to de- 
termine as many points as possible on the same level, and 
form thus, as it were, a parallel of elevation to the level of 
the sea. A line of this kind, traced at the altitude of, say 
one thousand feet, would determine in a considerable de- 
‘gree the physical condition of extensive spaces on the map 
on both sides of it. The stations of most interest will be 
found at the extremities of transverse arms of the ridge, or 
in the central and most retiring points ef the intervening 
spaces. Let the general slope of the country on both sides 
