WILSON.] METHODS OF TOPOGRAPHICAL WORK. 299 



ain-peaks, especially near their summits, are destitute of timber, while 

 the valleys are uniformly so, the timber in nearly all cases growing on 

 the slopes of the mountains. 



Therefore, from the mountain-peaks the drainage of the country is 

 clearly visible and sharply defined. Thus the topographer is often able 

 to trace the meanderings of a stream for mauy miles, as it recedes over 

 the distant plains or valleys. 



To do this class of topographical work successfully, requires a man 

 with a natural fiiculty for the recollection and recognition of objects 

 which he has seen from different positions, especially in a high, rough, 

 mountain country, where so many points are visible from one peak, 

 and where they undergo great changes in appearance as seen from differ- 

 ent positions. 



Yet this faculty may be cultiv{>ted to a wonderful degree when the 

 person is very careful and studies the relative positions of things, and 

 the individual forms and characteristics of mountain structure. It is 

 very much the same faculty that is required in recognizing faces, for each 

 mountain has its features and individual forms. It also requires men of 

 great physical endurance to carry on such work, owing to the many 

 difficulties and dangers that are met with in ascending so many rough 

 and high mountains, without any previous knowledge of the country. 

 The traveling is often difficult through these unknown regions, where 

 there is neither track nor trail to guide in the selection of a route, and 

 where one is compelled by the nature of the work to reach certain 

 points. 



DETEEMINATIONS OF ALTITUDES. 



The altitudes have been determined with mercurial barometers. Each 

 party is generally supplied with two barometers, and with extra tubes 

 and fixtures with which to repair any breakage that may occur. Base 

 barometers have been established at various points over the Territory, 

 always as near the district in which the work was being carried 

 on as practicable, which was often at a greater distance than was de- 

 sirable, the parties often working far beyond the borders of civilization. 



The heights of the mountain stations have been constantly checked 

 by a system of vertical angles between all occupied points, thus bind- 

 ing the whole together, so there are but few points depending upon a 

 single reading of the barometer for their heights, except the valleys 

 and such places as could not be thus checked. I give below an extract 

 from the report of Mr. Franklin Ehoda (who was my assistant during 

 the summer of 1874), which will serve to illustrate the method of con- 

 necting the points by vertical angles : 



"METHODS USED IN DETEEMININa THE ELEVATION OF POINTS. 



"All the elevations given in this report depend upon readings of a 

 mercurial barometer. Where a standard barometer whose elevation is 

 well determined is within a short distance, this instrument gives a very 

 good determination of elevation. In the past summer, however, it was 

 quite impossible to establish a base barometer in the vicinity of the 

 region surveyed, without great expense. All the readings had to be re- 

 ferred to distant stations. Eeadings on high peaks were referred to the 

 Signal-Service barometer on Pike's Peak at an elevation of 14,147 feet 

 above the sea, while readings on all points under 12,000 feet were referred 

 to the barometer of the United States Geological Survey at Fair Play, 

 whose elevation is 9,9o4.5 feet. The first of these is 150 irriles distant 



