42 FIELD GEOLOGY. 



steadily before his eye, lie inclines it until its edge coin- 

 cides with the bed being observed, and then reads off 

 as quickly as possible the angle indicated, and before 

 the position of the clinometer is shifted; to ensure 

 accuracy by this method, two or more observations 

 should be made and the results compared. 



In the two last-named instances the exposed face, 

 accessible and inaccessible the apparent dip is taken; 

 this may or may not be the true dip, which can be 

 greater, but cannot be less than that of the exposure. 

 Wherever possible, and unless the observer be certain 

 that he is getting the true dip, he should make two ob- 

 servations, the direction of one at a considerable angle 

 from that of the other, and work out the true dip by 

 one of the methods given in the following pages. 



The final results of observations taken with the cli- 

 nometer the amount and direction of the dip (if any) 

 of a bed or formation are shown on the map by the 

 symbols given in the table at page 33, drawn in vacant 

 spaces as near as possible to the spot where the sections 

 are exposed. 



To find direction of Dip, by diagram. When the 

 amount and direction of two lines of apparent dip are 

 known, the direction of the true dip may readily be 

 found by one of the following Kules, A or B. 



EULE A. When both the observed dips incline from 

 or towards the angle enclosed by their lines, fig. 11, the 

 true dip is at right angles to a line (a b) laid down by 

 the following method: 



Set off from the angle on each of the two lines of ap- 

 parent dip a number of units corresponding to the 



