VIII 

 PRIMAL ENERGIES 



HOW puny and meagre is the utmost power man 

 can put forth, even by the aid of all his 

 mechanical appliances, when compared with the 

 primal earth forces! Think, or try to think, of the 

 force of pressure that causes the rock-strata to 

 buckle or crumple or bend — layers of rock, thou- 

 sands of feet thick, made to fold and bend like the 

 leaves of a book — vast mountain-chains flexed and 

 foreshortened, or ruptured and faulted as the bend- 

 ing of one's body wrinkles or rips one's clothes. 

 Think of the over-thrusts and the folding and shear- 

 ing of the earth's crust. The shrinking of the earth 

 squeezes the rocks to an extent quite beyond our 

 power of conception. "So overpowering has been 

 the horizontal movement in some cases," says 

 Dana, "that masses of rock thousands of feet in 

 thickness have been buckled up and sheared, or, 

 simply yielding to pressure, have sheared without 

 folding, and been thrust forward for miles along a 

 gently inclined plane. These great reversed faults 

 are termed over- thrusts or thrust-planes. Some- 

 times such thrust-planes occur singly, at other times 

 the rocks have yielded again and again, great sheets 

 having been sliced off successively, and driven for- 



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