360 Forestry Quarterly. 



the point on the line at the base of the tree, the tip of which 

 was sighted upon. 



3. Crossing Exceptionally Steep Ravines. When crossing very 

 steep ravines, one accurate sight to the bottom, going down, and 

 one to the top, going up, will suffice, although the form of the 

 sides will suggest changing degrees of slope. On very steep 

 slopes the horizontal distance between contour intervals on the 

 map does not differ much for a change of 5% in slope or more. 

 It will be sufficient under the circumstances mentioned to show 

 upon the map sheet only the difference in elevation between the 

 two edges and the bottom. At the bottom of the ravine the com- 

 passman should indicate the grade of the ravine by sighting 

 straight down the water course. He enters this reading as a per 

 cent or degree of slope upon the stream or valley line. 



4. Lakes and Marshes. When offsetting to pass lakes or 

 marshes, the compassman can do away with sighting for obvious 

 reasons. With judgment he can ascertain the point on the line 

 at the opposite side of the marsh or lake which has the same 

 elevation as the point where the offset was made. 



5. Sighting in Dense Brush. Sometimes the compassman will 

 find it convenient to sight upon the tops of dead snags or stumps, 

 etc., on his line ahead of him. Taking a sight upon a snag or 

 stump in the brush ahead of him, he proceeds without further 

 sighting until within a few chains of the stump or snag. A sight 

 from this point on the line will give him data for a sufficiently 

 accurate approximation of the height of the stump or snag. Then 

 the compassman can calculate the difference in elevation between 

 the point of his first sight and the point on the line opposite the 

 stump or snag. In brushy areas the compassman will frequently 

 find such opportunities to do accurate sighting. The error in 

 elevation introduced by error in pacing will be corrected when 

 the horizontr.l distance between the two points is corrected by the 

 office man, or the camp draftsman. 



For sights taken parallel to the compass line, the angle or per 

 cent as well as the difference in elevation should be entered upon 

 the map sheet, the angle or per cent being placed on one side 

 of the line, indicating the sight, and the difference in elevation 

 between the two points on the other side of the line, indicating 

 the sight. 



Tying in. 



At the end of the strip the compassman enters the precise ele- 



