CHAPTER II. 



METHODS OF TOPOGRAPHICAL FIELD AND OFFICE WOEK. 



The secondary triaDgulation was carried on by the topographers, in 

 connection with the topographical work, with small theodolites reading 

 to minutes of arc, and carrying powerful telescopes ; the secondary 

 triangles summed up with a mean error of closure of about two minutes. 

 As this work was constantly checked by the primary points, the errors 

 could not accumulate sufficiently to be perceptible on the maps. 



The topographical field work was carried on in the following manner: 



First, the region of country to be surveyed was divided as nearly as 

 possible by natural boundaries into areas sufficiently large to emi)loy a 

 party the whole season. 



Before taking the field, the topographer supplies himself with all the 

 information possible as to character of country, &c., and collects all 

 the old maps that might give any idea of the existing trails, roads, or 

 places where supplies may be obtained. Each field-party is composed 

 of a topographer, geologist, assistant topographer, and sometimes a 

 botanist or zoologist accompanies them; these, with a cook, and two or 

 three packers, complete the party. The geologist and topographer work- 

 king in concert make a general plan for the summer campaign, and 

 equip themselves with all the necessary instruments and supplies. 



On reaching the district, they select the first commanding point 

 and ascend it ; on reaching the summit, the topographer sets up his 

 theodolite, while the assistant hangs up the barometer. 



The topographer proceeds to make a careful drainage sketch, on which 

 he indicates all features of note, while the assistant makes a care- 

 ful profile sketch of the entire surrounding country on a large scale. 

 Upon these sketches are marked, by numbers -or names, all the points 

 to be sighted, or in some cases the angular readings are placed upon the 

 sketches. 



After this is done, all peaks, points, ends of spurs, junctions of streams, 

 in fact every recognizable feature of t he surrounding country are sighted, 

 and the angles, both horizontal and vertical, recorded in a book, with 

 their numbers or names appended. 



From this first station are selected a number of points occupying 

 commanding positions, as points to be occupied as future stations, and 

 so on from each station there would be constantly selected points in 

 advance, on which stations were to be made. 



After finishing the work on the peak, the party proceeds to the next, 

 and there repeats the sketches and angles, taking great care to check 

 every previous sight possible, and taking all the new points that come 

 within range. 



Thus from day to day the country is sketched from every possible point 

 of view, and the points are each time sighted, giving many checks to the 

 location of all the more prominent features of the country. 



The mountainous regions of the country west of the Mississippi Eiver 

 are generally very favorable to this kind of work. Nearly all the mount- 

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