GEOLOGICAL MAPPING. 



Note. All maps are laid down on the paper with 

 reference to the true meridian, the proper allow- 

 ance having been made in their compass bearings for 

 the magnetic variation at the present time in these 

 Islands the needle points about 22 West of due 

 North. 



Compass and Protractor. It frequently happens that 

 it is necessary to identify on the map one's exact locality, 

 when the roads, fences, &c., shewn thereon do not afford 

 sufficient indication. For this purpose a Compass is 

 used ; an ordinary pocket compass of fair size will suffice 

 in most instances, and will give very nearly the position of 

 the place at which it is used ; but for greater exactness 

 -a prismatic compass is necessary. The latter is not quite 

 so easily carried as the pocket compass, although the 

 small prismatics now made and fitted in sling-cases are 

 very portable, and a Protractor also is required to plot 

 .the^result of an observation. 



Fig. 1. Compass and Clinometer. 



The pocket compass (fig. 1) generally has its circum- 

 ference divided into 16 parts the 4 cardinal points, the 

 4 intermediate, which divide the cardinals, as KW., &c., 



