BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 27, PP. 623-644 NOVEMBER 30, 1916 



TRIASSIC IGNEOUS ROCKS IN THE VICINITY OF 

 GETTYSBURG, PENNSYLVANIA 1 



BY GEORGE TV. STOSE AND J. VOLNET LEWIS 



(Read before Hie Society December 29, 1915) 



CONTENTS 



Page 



Distribution and mode of occurrence ; by George W. Stose 624 



Introduction 624 



Sedimentary rocks 624 



Igneous rocks 625 



Conclusions and history of Triassic events 629 



Petrography ; by J. Volney Lewis 630 



Summary 630 



General character of the diabase 632 



Textures 633 



Order of crystallization 633 



Varieties 634 



General description 634 



Normal diabase 634 



Feldspathic diabase, or anorthosite 635 



Quartz diabase 635 



Micropegmatite 636 



Aplite 636 



Hypersthene diabase 636 



Olivine diabase 636 



Basaltic diabase, or basalt 637 



Olivine basalt 637 



Petrographic details 637 



Pyroxene 637 



Hypersthene 638 



Plagioclase feldspar 638 



Orthoclase, microcline, quartz 638 



Magnetite 639 



Biotite 639 



Olivine 639 



Apatite 639 



Pyrite and chalcopyrite 639 



1 Manuscript received by the Secretary of the Society May 12, 1916. 

 Published by permission of the Director of the TT. S. Geological Survey. 



(623) 



