APPENDIX E 



COMPASS AND CLINOMETER 



Any ordinary pocket-compass, if not too small, will serve to take the 

 direction of dip. The one in common use by field geologists is divided 

 into graduated quadrants. From North and South points, the figures in 

 each quadrant run up on either side to 90. In taking an observation, 

 allowance must be made for the declination or variation — magnetic north 

 in these islands, at the present time, being about 20° west of true north. 

 As all maps are constructed with reference to the true meridian, it is 

 necessary that the dip-arrows we insert should likewise indicate true and 

 not magnetic directions. In recording an observation of dip, we say that 

 the direction is so many degrees west of north, east of south, north of 

 west, and so on, as the case may be. Thus N. 25 W. means 25" west of 



north, and corresponds therefore to the intermediate compass-point 

 of NNW. 



Not infrequently, owing to the absence or paucity of streams, roads, 

 fences, buildings, etc., the geologist may sometimes have difficulty in 

 locating the position upon the map of some outcrop or other field data, 

 which he desires to indicate. In order to do so he must of course take 

 bearings with the compass, for which purpose such an instrument as that 

 shown in the accompanying illustration is usually sufficient, but if great 

 accuracy be demanded a prismatic compass will be necessary. After 



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