BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 VOL. 29, PP. 375-392 SEPTEMBER 20, 1918 



PEECAMBRIAN SEDIMENTARY ROCK 

 OF EASTERN PENNSY 



BY EDGAR T. WHERR^ ^ 



{Presented in abstract before the Society i) "" ' wu .^ 



CONTENTS 



Page 

 Introduction 375 



General geology 377 



Crystalline limestone 378 



CliaracteT 378 



Origin 379 



Quartz-mica schist 379 



Character 379 



Origin 382 



Magmatic modification 383 



Graphite-bearing quartzite 385 



Character 385 



Origin : 386 



Magmatic modification 386 



Basic ( amphibolite ) gneiss 388 



Character 388 



Origin 390 



Summary 392 



Introduction 



Precambrian rocks are exposed in Pennsylvania in three belts — the 

 South Mountain belt, which is a northward extension of the Catoctin belt 

 of Maryland and terminates a few miles southwest of Harrisburg, owing 

 to covering by Paleozoic and Mesozoic sedimentary rocks; the Piedmont 

 belt, which extends from the Maryland line at the Susquehanna River 



* Manuscript received by tlie Secretary of tlie Society December 13, 1017. 



1 Tlie greater part of ttie worli herein described was done while the writer was teach- 

 ing at Lehigh University. It was completed during his connection with the U. S. Na- 

 tional Museum. The paper was presented in abstract at the meeting of the Geological 

 Society of America December 28, 3 916; an abstract was printed in Bull. Geol. Soc. Am., 

 vol. 28, 1917, p. 156. " ' 



XXIX— Bull. Geol. Soc. Am., Vol. 29, 1917 (375) 



