BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 2, pp. 155-164, PLS. 4, 5 FEBRUARY 11, 1891 



THE STRUCTURE OF THE BLUE RIDGE NEAR HARPER'S 



FERRY. 



BY H. R. GEIGER AND ARTHUR KEITH. 



{Read before the Society December' 31, 1890.) 



CONTENTS. 



Page. 



Description of the Region 156 



Geographic Position 156 



Topography and general Geology 156 



Surveys in the Region 156 



The Problem of the Area 157 



Views of the Authors 157 



Former Views 157 



General Relations of the Beds 157 



Areal Distribution and Structure of the Roclcs. 158 



Symmetrical Distribution of Rocks 158 



Synclinal Structure of Ridges 158 



Topographic Forms express Rock Character _. 159 



Significance of Structural Details 159 



Superposition of Shale and Sandstone 159 



Possible Faulting 159 



Actual Conformity shown by (a) Interbedding, (b) uniform Position of 



Limestone, and (c) uniform Thickness of Shale 160 



Limitations of possible Faulting shown by (a) Symmetry of Folds, 

 (6) width of necessary Fault Plane, and (c) Absence of Beveling of 



the Rocks 160 



Faulting an Assumption 161 



Analogous Sections 161 



Region west of the Blue Ridge 161 



Homology between Massanutten Mountain and the Blue Ridge 161 



Sections at Turk's Gap, Buchanan and Christiansburg 161 



Contrasted Sections, as at Balcony Falls and Dublin 161 



Existence of two Sandstones 162 



Summary 163 



Discussion 163 



XXIII— Bull. Geol. Soc. Am., Vol. 2, 1890. (155) 



