J.W. Powell's Survey of the Rocky Mountain Region. 347. 
sketched. The instrument is also furnished with a graduated 
circle on which horizontal angles may be read to the nearest 
half minute, and this circle is used for the secondary triangula- 
tion. The orograph and plane-table are used conjointly, and 
their results furnish data for the production of contour maps. 
It is believed that by their introduction the quality of topo- 
graphic work has been much improved, without addition to its 
cost. hen a topographer takes the field with these two 
instruments and plane-table sheets on which the primary trian- 
gulation has been previously plotted, he returns with a map on 
which all of the geographic features to be delineated have been 
determined by their angular relations and the scenic character: 
istics necessary to give proper effect to the maps, have been 
outlined by instrumental means. In this manner the subse- 
quent construction of maps at the office ready for the engraver is 
reduced to a minimum of labor, while for the proper accuracy 
the topographer is not necessitated to resort to his memory for 
the appearance of the landscape, but only to the definite record. 
rometers.—T he instruments used in the hypsometric work 
yehrom- 
’ 
are Green’s mercurial mountain barometers, Green’s ps 
Classification of Lands by Mr. Gilbert—The Survey under 
the se. of ee Powell has been extended over the 
