342 A. KEITH OUTLINES OF APPALACHIAX STRUCTURE 



application of force. The first attempts to explain the great upheaval 

 and tilting of the rocks were simply to call into being for each case a 

 special convlusion of the earth. The various upheavals or systems of 

 folded mountains were seen on closer knowledge to possess many features 

 in common. The recognition of this led to the belief that there was an 

 orderly system in the matter and that all folded mountain ranges and 

 the larger deformations were produced in much the same way, although 

 at different periods. With the introduction of this element of order the 

 accjuirement of knowledge of mountain-building became better directed 

 and less speculative. Causes whose nature are unknown were in the main 

 set aside and attention was chiefly focused on connecting with the prob- 

 lem causes which were ^I'ithin the experience of man or could be justly 

 deduced from the facts of observation. 



In recent years there are indications of a return to advocacy of causes 

 which can not be determined to exist and which are outside of the realm 

 of human experience. Speculation of this order has its merits, but its 

 drawbacks are also obvious and may become an obstruction rather than 

 a help to progress. The final test of all theories lies in the facts of the 

 field, and any theory fails which does not satisfy that test. The number 

 of theories proposed to explain mountain ranges is large; indeed, it is a 

 tribute to the intelligence or ingenuity of man that so many different 

 conclusions as to cause can be drawn from a given set of facts which 

 appear at the outset to be simple. Xo attempt can be made to test the 

 theories exhaustively in these pages, and only their major points will be 

 discussed. The wide divergence between the theories shows that the 

 field need not be considered closed to new ones. 



The first theory as to the cause of the Appalachian folds was set forth 

 by Eogers, w^ho likened the folds to a set of huge waves, with the impli- 

 'cation that they were produced in succession and in a similar manner. 

 This theory really did no more than to call on a special convulsion for 

 them. Later theories were based in part at least on kno\Aax physical 

 principles and had their merits. They are of two general classes — first, 

 those which depend on forces coming from outside of the earth and, 

 second, those which rest on forces derived from the earth itself. 



The theories of the astronomical class have been repeatedly analyzed 

 by mathematicians and astronomers and have been found to possess de- 

 fects which are serious if not destructive. Such, for instance, is the 

 theory that the moon was originally part of the earth, but parted com- 

 pany from it as a result of a higher rate of revolution than now exists. 

 The other conditions and results of such a separation are such that no 

 credence is given to the theory in connection with momitain-building. 



