310 A. KEITH OUTLIXES OF APPALACHIAX STRUCTrRE 



Page 



Theories as to cause of deforming forces 341 



Early theories 341 



Contraction 343 



Suboceanic spread 345 



Isostasy 346 



Geosyuclines 351 



Continuity relations 353 



Continental creep 354 



Summary of theories 361 



Batholith intrusion as cause of folding 365 



General statement 365 



Probabilities 366 



Analogies 367 



Examples 368 



Method of attaining horizontal motion 369 



Fluid condition 369 



Attitude of rock partings 370 



Included gases 372 



Growing crystals 373 



Bearing on other theories 373 



Ultimate forces 375 



General statement 375 



Heat 375 



Gravity 376 



IXTRODUCTIOX 



Tlie subject of Appalachian structure is one of the most interesting 

 in geology in that it affords the greatest example of mountain structure 

 in the world. All stages of deformation from undisturbed rocks to beds 

 folded, overturned, broken, mashed, and metamorphosed are seen 

 throughout the entire length of the system, 2,000 miles from Alabama 

 to Xewfoundland. The connecting links between the types of structure 

 are finely exposed and the chain is complete. Tlie rocks exposed range 

 from earliest Precambrian to Tertiary, and the depths of the earth are 

 laid bare in the heart of the range in a manner nowhere equaled. 



The beginning of the study of the Appalachians practically coincides 

 with the beginning of American geology about 100 years ago. The prin- 

 cipal structures of the folded sediments were made known ])y the work 

 of tlie Eogers brothers in Pennsylvania and A'irginia about 80 years ago. 

 Substantial contributions were made bv many of the earlv wolog-ists on 

 the various State surveys, such as Hall, Emmons, Safford, Lesley, Smith, 

 White, and Stevenson. Such leaders as Dana, Logan, Dawson, Seh^'^'n, 

 and Hitchcock added to Appalachian knowledge in important ways. 



