WILSON ON GEOGRAPHICAL WORK OF THE SURVEY. 735 

 OFFICE-WOIIK OF THE TOPOGRAPHER. 



On the return of the parties to the office, the topographers would each 

 calcuhite aud construct a projection on a scale of two miles to one inch, 

 on heavy mounted drawing-paper. On each sheet would be plotted, by 

 latitudes and longitudes, all the primary points that had been located 

 in the district, with a sufficient number of secondary points from which 

 to plot the remainder of the stations, with large eight-inch circular pro- 

 tractors reading to minutes of arc. 



After locating all the stations, they establish all the points that 

 have been sighted from the numerous stations, upon the sheet. When 

 all the points are placed upon the sheet in the foregoing manner, the 

 drainage is located by plotting first all points along tlie streams that 

 have been sighted, such as junctions, noted bends, «&c., then filling in 

 all the minor details from the drainage-sketches, carefully studying all 

 the different sketches that contain the streams in question. 



The sketches are made on a scale from three to four times larger than 

 that at which the final maps are plotted ; so there is generally more de- 

 tail on the sketches than can be represented on the maps. Plates 36 

 and 37 represent these sketches, and are actual tracings from the field- 

 book, with the notes, &c., as taken from stations 115 aud 125 by my- 

 self. 



Turning to the sketch, it will be seen that every junction and impor- 

 tant bend is sighted, and that all the i^rominent peaks are indicated in 

 their relative positions as nearly as could be judged, t/omparing this 

 with the map as plotted (see Plate 39), we find that it is somewhat 

 distorted, as might be expected when we consider that the sketch was 

 made entirely by guess. But at the same time it will be seen, after all 

 the points are actually located, that the remainder of the drainage can 

 be sketched in very approximately. 



Now we have the frame-work of the map upon the paper; it is inked 

 in and we are ready to commence the drawing of the hill-structure, which 

 we indicate by contour-lines, each representing 200 feet of vertical 

 distance. By these lines we propose to give the approximate heights 

 as well as forms of the mountains as nearly as we know them from the 

 numerous height and profile sketches which we have taken from every 

 occupied station. I will state here that I do not attempt in this paper 

 to give all the minor detail of this work, proposing only to give a gen- 

 eral idea of the methods used in constructing the maps. First, all the 

 heights are calculated and tabulated in some convenient form for refer- 

 ence. 



Having our points and drainage located, we start, for instance, with 

 the heights of the points («) and {!>) (see Plate 38); the difference be- 

 tween these two points we find to be about 3,000 feet, the contours being 

 200 feet apart, we will have fifteen to be distributed between these two 

 points ; they are accordingly spaced in from the sketch nearer together 

 or farther apart as the slope is greater or less. Next we find the point 



