9s 



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72 Causes of Geological Change 



upon it in a large fair hand, except that a few of the 

 letters are incomplete. These letters are not cut in the 

 stone^ nor do they consist of any foreign substance, like 

 ink, or paint, spread over it. But they are rendered 

 visible simply by the lighter color of the surface, where 

 they were originally written, probably with some sort of 

 paint, which for a time prevented the rock beneath it 

 from decaying, while the decomposing process went on 

 gradually on the other parts of the stone. By passing 

 the fingers over the letters we perceive that they project 

 a little, though scarcely enough to be visible to the eye. 

 Now as this inscription must have been made since the 

 settlement of that part of the State by the whites, we 

 cannot suppose that more than one hundred and fifty 

 years, at the longest, have since elapsed ; and probably 

 the period is much less. We have here, then, an imper- 

 fect measure of the rate at which hard quartz rock will 

 decay by atmospherical agencies ; though we cannot say 

 but it may have been many years since the paint, with 

 which the letters were made, was so worn off that these 

 as well as the other parts of the surface of the stone, 

 have been subject to decomposition. 



ALLUVIUM OF DEGRADATION. 



In mountain ridges, where one or both sides are nearly- 

 perpendicular naked rock, especially trap rock, frost 

 commences the work of crumbling them down. Water 

 penetrating the fissures of these rocks, expands by freez- 

 ing, and forces them slightly asunder. This makes room 

 for a larger portion of water the succeeding winter ; and 

 thus the process goes on, until the columnar masses of 

 rock are ure-ed downward hv th^ ('^■^ — „r -. j 



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