

CURVATURE OF STRATA 129 
section, for example (Fig. 11), the beds at a seem to be 
horizontal, when in reality they dip at a considerable angle, 
as shown at J—where the cliff runs in the direction of the 
true dip—the direction and amount of which can therefore be 
readily determined. Not infrequently, however, cliffs and 
other cuttings or sections traverse the dip of the strata 
obliquely, and when such is the case, the apparent dip shown 
by the edges of the exposed beds does not indicate either the 
exact direction or the full amount of the true dip, which is 
always greater than that of the apparent dip. When the 
observer suspects that the inclinations exposed in two 
adjacent sections are only apparent dips, he may yet find the 
Epensadirection by the geometrical method referred to in 
Appendix C. Asa rule, however, an apparent dip can rarely, 





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FIG. 11.—APPARENT AND TRUE DIP. 
if ever, deceive one who is not content to view sections from a 
distance. Close examination will rarely fail to discover on 
even the smoothest of cliff-faces, irregularities — ledges, 
depressions, entering and re-entering angles, etc-—in one or 
other of which the upper or under surfaces of the bedding- 
planes are almost sure to be disclosed. 
In hilly and mountainous tracts, the exposed ends of 
strata often present a fallacious appearance of dip, which has 
occasionally led to mistakes. The appearance referred to is 
known as “terminal curvature” or “surface creep,” and is 
illustrated in the accompanying figures (Figs. 12a, 120). An 
observer ascending the mountain slopes shown in the 
diagrams might quite well be deceived by the apparent dip 
of the beds, if-it did not so frequently happen that the true 
dip of the rocks in such a region is usually exposed in 
numerous torrent-tracks and gullies. The origin of terminal 
curvature is obvious enough—being solely the result of 
I 
