CHAPTER XI 



CURVATURE OF ROCKS 



ALONG the limited exposures of strata usually visible, such 

 as those in the bed of a stream, or a tea-chore, in a railway 

 cutting or in a quarry, the planes of dip usually seem in 

 section to be straight lines. Bed succeeds bed inclined 

 at the same angle and forming a succession of parallel 

 bands. But could we continue the sections downward 

 beneath the surface, or see the rocks exposed on the bare 



Fio. 4-- 



steep side of a great mountain, we should observe that 

 though, when examined within the limited area of a few 

 feet or yards, the beds look as if they sloped in straight 

 stiff lines, in reality they are portions of great curves. 

 That this must be so is made evident when we reflect on 

 what must be the consequence of the variations of angle 

 in the inclination of beds at the surface. Suppose, for 

 example, that along the ravine of some river, or in any 

 other natural or artificial opening, we encounter a suc- 

 cession of strata inclined as in Fig. 42. We cannot 

 I 



