STRUCTURAL GEOLOGY 



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the direction of the horizontal edge of dipping beds, or more gen- 

 erally, the direction of a horizontal line along the outcropping edge 

 of a dipping bed, as illustrated in Fig. 309. Since the strike is 

 always at right angles to the dip, the strike need not be recorded 



Fig. 309. Diagram illustrating dip and strike. (J. Geikie.) 



Fig. 310. The compass and clinometer. The black bob at the bottom 

 points to 0. If the base of the clinometer were depressed at the right, 

 the bob would swing over to 10, 20, 30, etc. 



if the direction of the dip is. Thus dip 40, S. 20 W. is the same 

 as dip 40, strike N. 70 W. 



When beds incline in a single direction, they form a monocline. 

 When they are arched up as in a fold, they form an anticline (Figs. 

 16 and 17). The anticline may depart from its simple form, 

 as shown in Fig. 311. The downfold corresponding to an anticline 

 is a syndine (Fig. 312). When beds assume the position shown 

 in Fig. 18, the folds are isoclinal. When considerable tracts are 

 bent so as to form great arches or great troughs with many minor 



