THE SCIENCE OF OBSERVATION. 



47i 



either with or without folding of the strata. These initial wrinkles 

 pave rise to our first mountains, and the continuation of these con- 

 ditions at the present time is as surely nourishing mountain growth 

 as at any time in the past. In this way the fluctuations of the ocean's 



Fig. 7. — Mountain showing Rock Folding. 



level, above referred to, alone are to be explained, and such form 

 but temporary rises and falls in the history of a continent. 



The rate at which an ocean bed is raised to form a mountain 

 range is, no doubt, a variable one ; always slow, often interrupted, but 

 seldom or never violent. During this time the strata usually undergo 

 crushing and folding; stretching takes place, and displacements of the 

 rocks, or faulting, are not uncommon. As an example of the wrink- 

 ling that the strata may suffer under these conditions, the reader is 

 referred to the beautiful symmetrical fold shown on the side of a 

 mountain in the Appalachians (Fig. 7). Similar folding is the 

 rule, but often immense areas are raised to great heights above the 

 •ocean without disturbing the horizontal position of the beds (see Fig. 

 -8). Coincident with the emergence of the rocks from beneath the 



