234 jPogue, Jr. — Geology and Structure of Volcanic Rocks, 



for six miles and agrees in direction with two large diabase 

 dikes. They are also roughly parallel to the strike of a pro- 

 found fault a few miles to the west, which Laney* has shown 

 to separate the slate series from a large area of igneous rocks. 

 A large overthrust fault has been indicated as extending 

 along the eastern border of Flat Swamp Hidge in a northeast 

 direction and becoming northerly in trend near the upper 

 borders of the map. Its presence seems necessitated by the way 

 in which broad belts of rock appearing on the western slope of 

 Flat Swamp Ridge are not repeated on its eastern declivity, as 

 would be expected on the two limbs of a syncline. Either, 

 then, beds one-half mile or so in thickness must thin out along 

 their dip in the course of a mile or they must be abruptly cut 



Fig. 3. 





a, i,i i < mil, 





.i ' 





v > > <J 







HH 



+ + + + -t- 

 + + •»•+ + + 



+ + + t- + 





"" "x 



si 



AT 



An-V-Br An-T-Br 



An 



Gb 



PrF 



Fig. 3. Cross-section along the line AB of the geologic map. 



Explanation of contractions : SI, slate ; AT, acid tuff ; An-V-Br, acid vol- 

 canic breccia; An-T-Br, andesitic tuff and breccia; An, andesite: Gb, gabbro; 

 Pr.F, probable faults. 



off by a fault. A glance at the cross-section will make this 

 point clear. 



The faulting is probably the result of the same compressive 

 force which induced folding, schistosity, and jointing. It is 

 unnecessary to bring in a second great earth movement to 

 explain this structure. Yet it is possible that the coming to 

 place of great granitic batholiths a few miles to the west may 

 have exerted sufficient compression to occasion overthrust 

 faulting. 



Interpretations of structure. 



Most probable interpretation. — The reasons have already 

 been presented for believing the region to be made up of a 

 series of inclined folds, whose axial planes dip steeply to the 

 northwest. This interpretation is represented on the accom- 

 panying cross-section. 



In a region, such as the one under consideration, in which 

 the structural features are so obscure and difficult of access, a 

 diagram can only attempt to express in a generalized maimer 

 the actual conditions. 



*Laney, F. B., The Gold Hill Mining District of North Carolina. A 

 Thesis, Yale University, 1908, p. 112. 



