


292 STRUCTURAL AND FIELD GEOLOGY 
width of individual outcrops similarly varies with the degree 
of inclination: beds dipping at a low angle yielding a 
relatively broad outcrop, while the same beds dipping at a 
high angle present a relatively narrow outcrop. Thus the 
outcrop of a bed of uniform thickness will appear broader or 
narrower as the dip diminishes or increases. 
Vertical Strata.—The outcrops of vertical beds are practi- 
cally uninfluenced by the form of the ground, and display, of 
course, the true thickness of the strata. 
Measurement of Thickness of Strata.—When strata are 
horizontal, it is obvious that their thickness can only be 
$80 YARDS 
a 

FIG. 112.—MEASUREMENT OF INCLINED STRATA. 
measured when they are exposed in section, as in sea-cliffs, 
river-valleys, etc. If we know the heights above sea-level 
reached respectively by the lowest and uppermost beds of 
a great series of horizontal strata, we of courselknow at the 
same time the thickness of the strata. So, again, in the case 
of vertical strata it is obvious that a line measured exactly 
across the strike of the beds will give us their thickness 
between any two selected points. But when strata are 
inclined, the width of their outcrop is necessarily greater 
than the actual thickness of the beds. By meansogiga@ 
protractor, however, there is no difficulty in measuring the 
thickness of a series of strata, inclined at a known angle 
between any two given points. Thus, in the diagram (Fig. 

