132 STRUCTURAL AND FIELD GEOLOGY 
the lower the angle of dip, the wider the outcrop (see Fig. 15). 
As the dip increases, the width of the outcrops gradually 
diminishes until the strata become vertical, and then the 
width of outcrop can be no more than the actual thickness 
of the beds. 
The accompanying diagram (see Fig. 16) may suffice to 
illustrate how the width of an outcrop is affected by surface 
features. The beds 1, 2, 3, as seen in section, are Gt equa! 
thickness, but their outcrops, owing to the shape of the 
ground, vary much in width. Bed 1, appearing upon relatively 
flat land, yields a broad outcrop; bed 3, forming the surface 
of a gently inclined plateau, covers a much wider area; while 

Fic. 16.—WIDTH OF OUTCROP AFFECTED BY FORM OF GROUND. 
bed 2, coming out on a steep slope, would show upon a map 
an outcrop somewhat narrower than the true thickness of 
the stratum. 
Strike is a line drawn exactly transverse to the dip. 
Thus beds with an east dip have a north and south strike. 
The strike rarely coincides with the outcrop; usually it only 
does so in the case of vertical strata, the outcrops of which 
are not affected by the form of the ground. Now and again, 
however, when the edges of strata inclined at any angle crop 
out upon a level plain, outcrop and strike may coincide. The 
term strike is generally used by geologists when they are 
referring to the average direction of an outcrop. Thus a 
great succession of strata having a persistent or dominant 
dip, say towards the north, are said to have an east-and-west 
strike, no matter how sinuous and irregular the outcrops 
