
‘Parr IV] CURVATURE OF ROCKS. 515 
change of inclination, it is evident that the beds cannot proceed in- 
definitely downward at the same angle which they have at the surface, 
otherwise they would run away from each other, but must bend 
round to accommodate themselves to the difference of inclination. 
By prolonging the lines of the beds for some way beneath and above | 
sea-level, we can show graphically that they are necessarily curved 
(Fig. 234). <A section of this kind brings out clearly the additional 
fact that an upward continuation of the curved beds must have been 
carried away by the denudation of the surface. In every instance 
therefore where, in walking over the surface, we traverse a series of 
strata which gradually, and without dislocations, increase or diminish 
in inclination, we cross part of a curvature in the strata of the earth’s 
crust. The foldings, however, can often be distinctly seen on cliffs, 
om 
2-- 
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2 Z Z 7 4 Ze 











7 at 
oe s 7 4 = 7 KEY 3 4 ft 
, << WW SX Oy LQ Ie 
sak cas 2 SE WG WS S \N\ WSS NS 
SS RSE Sw \ XV XS = 
= SINE 
Say a 7 7 £ 
-=——-—s wae Z (f 7 / / a 
4 / 
a“ 4 
-— a 7 ys - 4 
Fic. 234.—Sxction oF INCLINED STRATA, AS IN Fic. 233, SHOWING THAT THEY FORM 
Part oF A LARGE CURVE. 
coast-lines, or other exposures of rock (Fig. 235). The observer 
cannot long continue his researches in the field without discovering 
that the strata composing the earth’s outer crust have been almost 
everywhere thrown into curves, usually so broad and gentle as to 
escape observation except when specially looked for. 
If the inclination and curvature of rocks are so closely connected, 
a corresponding relation must hold between their strike and curvature. 
In fact, the prevalent strike of a region is determined by the direc- 
tion of the axes of the great folds into which the rocks have been 
thrown. If the curves are gentle and inconstant there will be a’ 
corresponding variation in the strike. But should the rocks be 
strongly plicated, there will necessarily be the most thorough 
coincidence between the strike and the direction of the plication. 
Monoclines.—Curvature occasionally shows itself among hori- 
2L 2 
