380 A. KEITH OUTLIXES OF APPALACHIAN STRLXTURE 



by scores of geologists and are not open to serious challenge. While the 

 theory was framed for the Appalachians, it fits other systems reasonably 

 well and may serve as a basis for further investigation of them. It adopts 

 many of the great facts and processes on which other theories are based, 

 notably those of suboceanic spread and isostasy. and forms a consistent 

 and reasonable whole. It has a flexibility in regard to time and space 

 possessed by no other theory. Its actuating power does not accumulate 

 steadily and require rhythmic action, like shrinkage, nor is it exhausted 

 in one convulsion, as in partition of a satellite. Its results are related 

 to the heavy masses of the earth and not to meridians and parallels, so 

 that no upsetting of earth constants is demanded. Finally, it is adequate 

 in quantity, as few theories are. 



It is not in the nature of things that this theory, or any on the same 

 subject, should be fully proven, but it is hoped that its derivation from 

 the Appalachian facts, its reliance on established physical principles, and 

 its accordance with the conclusions of other sciences will gain for it 

 serious consideration. 



