82 FIELD GEOLOGY. 



laid down, or at all events pricked off, by the datum line, 

 from the point where crossed by the vertical line (on 

 which point the centre of the protractor would be placed), 

 and then transferred to its proper position as starting 

 from the bench-mark. The measured distance is then 

 scaled off along the inclined line, and another vertical 

 line in pencil drawn through the measured point and 

 through the datum line. This point is the second 

 station, and a figure 2 is made below it for the conveni- 

 ence of future reference. Another line is now laid down 

 in a similar manner for the " fore-sight ;" this being an 

 " elevation " forwards rises in the same direction as the 

 one already plotted, is laid down, measured off, and 

 numbered. The succeeding observation is a " back- 

 sight " and " elevation," therefore " depression " forwards, 

 and will be laid down with a different inclination from 

 those previously drawn. 



These lines of course do not accurately represent the 

 curved parts of the surface, but give correct heights at 

 the points selected for stations ; the line, when inked in 

 between, must sweep naturally through these points, and 

 the sketch lines in the level-book supply the shape of 

 the intervening ground. Wherever a station is on a 

 road, or by a stream, a pit, and so on, the fact must be 

 recorded on the section ; and wherever the line crosses or 

 passes by such points between the stations, note must 

 be made of the intermediate measurement to them that 

 their position may be correctly indicated. The section, 

 fig. 19, has some working lines dotted at the left hand ; 

 these represent the stations, and in practice would be 

 drawn in pencil, to be erased when the surface line with 

 the roads, &c., had been drawn in Indian ink. 



