130 A MANUAL FOR NORTHERN WOODSMEN 



denied, however, that rapid weather changes sometimes 

 make accurate work difficult. 



Some interior mountain territory is characterized by 

 lightly forested ridges contrasting with great density of 

 timber and brush along the streams, while logging methods 

 are often such that accurate knowledge of grades on valley 

 lines is not essential. In circumstances such as these, 

 circuits of transit and stadia work carried over the ridges 

 have proved a satisfactory method of height control. 

 When areas concerned have never been covered by the land 

 surveys, angles have been turned and read in addition for 

 the purpose of control in the horizontal direction. 



With control laid out in this way the early plans of 

 reconnaissance in such country involved, as the next step, 

 the crossing of valleys with strip surveys, the aneroid 

 being relied on for elevation. This plan of work, starting 

 from known points on the ridges and running long lines 

 independent of one another, crossing the brooks and valley 

 bottoms (where grade was most important) at a long 

 distance from known bases both horizontally and verti- 

 cally, made demands on the aneroid which it was not able 

 to meet successfully. 



Height work along the stream lines was an evident 

 corrective, but a substitute scheme that at the time of 

 writing seems to be filling the requirement is the use of the 

 tape and clinometer. 1 Both instruments have, however, 

 been subjected to modification. The clinometer has been 

 made more efficient in numerous ways; in particular the 

 arc has been enlarged and so graduated that instead of 

 degree or per cent of slope it gives difference of elevation in 

 feet for the given slope and a stated distance (66 feet or one 

 chain in present practice). The tape used for the purpose 

 is 2$ chains long, two chains of it marked in links as usual, 

 while the extra length or "trailer" is so graduated that 

 the inclined distance along any slope which corresponds to 

 two chains horizontal may be set directly. By these 

 devices two short cuts are accomplished : first, difference in 



1 For a fuller description of this method see "The Timberman," 

 March, 1916. or "Engineering News," Vol. 75, No. 1, p. 24. 



