Theories of the Formation of Mountains. 419 



.0087265 (or the sine of 30') we have 364553.900'7500 for the 

 lenojth of the chord of an arc of one deo^ree : Then 



Arc of 1° 364560.01041687 



Chord of 1^ 364553.90075000 



Diflference 6.10966687 



The difference between the lengths of the chord and the arc 

 of 1^ is thus only about 6 feet and one inch. Therefore if we 

 take any section across the Appalachians, of about 70 miles in 

 length the greatest amount of plication that could have resulted 

 from subsidence within it, would be a single fold, which at the 

 most could not be three feet in height. 



But there is scarcely any section of that length across the dis- 

 turbed region, commencing from the eastern side, that does not 

 exhibit the remains of four or five folds which before they 

 were obliterated by denudation must have been a mile in height 

 each. Let it be granted that there were originally four of such 

 folds, and that each curve was equal to a semicircle. Then the 

 difference between the length of a line following the surface over 

 the four hills, and down into and across the bottoms of the four 

 valleys, and one drawn straight through their bases, would be 

 4.5660 miles, or about four miles and a half. In other words to 

 produce these four ridges of hills, the strata must have been 

 shoved or compressed laterally four miles and a half, while by 

 Professor Hall's process, the greatest possible distance could only 

 be six feet and one inch. And further, in addition to this en^ 

 ormous deficiency there is a great deal more to be accounted for. 

 Between and on every one of the principal folds there are very 

 numerous smaller parallel ones. Taking all these together with 

 the principal flexures, the amount of the lateral thrust or com- 

 pression across the whole belt has been more probably eight or 

 ten miles. 



Viewed in this way the theory of plication from subsidence 

 appears to fail altogether. Another objection to this theory is 

 founded on the fact admitted by all parties that at least with one 

 or two interruptions the subsidence has been gradual and the 

 whole amount sav 40000 feet distributed throu2jhout the enormous 

 period of time which elapsed during the Silurian Devonian and 

 Carboniferous epochs. No man can give the length of this 

 period, but it must have been very great. Let it be granted at 



