Appalachian Faulting, 267 



anticlines The former is overturned eastward and the latter 

 is overturned and faulted, the plane of the thrust-fault dipping 

 steeply toward the west. The latter case is the one mentioned 

 by Dr. Smith as illustrating his type of so-called " underthrust 

 faults." The structure is shown in the sections accompanying 

 the Gadsden Atlas Sheet.* 



Comparing the thickness of the Carboniferous formations 

 of this region we are able to reconstruct the original syncline 

 of deposition which has determined the location and form of 

 the Murphree Yalley fold. In other parts of this region there 

 is a very gradual westward thinning observable in all the Pale- 

 ozoic formations implying, if any, very moderate eastward 

 initial dips. In this particular locality, however, the Lookout 

 sandstone, the lower portion of the coal measures, has its 

 maximum thickness of 800 feet in the Blount Mountain syn- 

 cline ; from this it thins rapidly westward to 60 feet or less 

 west of the Murphree Yalley anticline and also eastward, 

 though less rapidly to Chandler Mountain. Hence there must 

 have been an original syncline of deposition whose axis coin- 

 cided with the Blount Mountain syncline and which had 

 initial dips eastward steeper than those westward. These 

 initial eastward dips were sufficiently pronounced to produce 

 an overturn toward the southeast. The form of the fold natu- 

 rally determined the dip of the thrust-fault when faulting 

 was developed as a secondary effect of continued compression. 



Since the Murphree Yalley fold shows a further stage of 

 development than the southern portion of the Wills Yalley 

 fold it may perhaps properly be regarded as an original step- 

 fold developed on the westward side of the syncline of deposi- 

 tion while the latter is the consequent fold. 



The reason for the eastward overturn in the second case 

 mentioned, the northern end of Wills Yalley, is more obscure 

 than in the case of Murphree Yalley. The form of the 

 fold is shown on the Stevenson Sheet f It is quite pos- 

 sible that the coal measures thicken eastward from Fox 

 Mountain toward the Lookout Mountain syncline, indicat- 

 ing an initial eastward dip sufficient to determine the direc- 

 tion of overturn of the resulting fold. Whatever may have 

 been the cause of the abnormal form which the fold assumed 

 it was purely local, for the fold becomes symmetrical a few 

 miles from its northern end and thence southward assumes the 

 normal form with overturn toward the west. 



Direction of the compressing force. — Thus far the origin 

 and direction of a force adequate to produce folding and fault- 



* Geologic Atlas of the United States, Gadsden Folio, Geology by C. W. Hayes. 

 In press. 



•f Geologic Atlas of the United States, Stevenson Folio, Geology by C. W. 

 Hayes. In press. 



