GEOLOGICAL SECTIONS. 47 



face, where it has been observed (in this case 20), and 

 the direction of true dip found, by Eule A. Let the 

 face-line itself form the base (a e, fig. 15, or c e, 

 fig. 16) of the triangle, thus saving trouble, and making 

 the method, perhaps, more readily understood. It is 

 found that in the distance a e (or c e, fig. 16) the 

 bed rises a certain number of feet or inches, but along 

 the line of true dip, e / (or c d, fig. 16), it of course 

 rises the same number of feet or inches. Set off this 

 amount of rise then at right angles to the true dip as 

 in the other case it is at right angles to the apparent 

 dip and draw a line from the point g, thus marked 

 off, to the point e (or c, fig. 16), where the rise com- 

 mences, the angle enclosed (25, fig. 15, and 21, fig. 16) 

 is the measure of the true dip. It must necessarily be 



Fig. 16. 



a greater angle than that of the apparent dips observed, 

 because the bed rises to the same height in a shorter 

 distance. 



