BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 34. pp. 507-524 September 30. 1923 



OEDOVICIAN OVEELAP IN THE PIEDMONT PROVINCE OF 

 PENNSYLVANIA AND MARYLAND ^ 



BY GEORGE W. STOSE AND AJs^NA I. JONAS 



{Presented before the Society December 29, 1922) 



CONTENTS 



Page 



General relations 507 



Details of the Conestoga overlap 510 



Fossils and correlation 520 



Summary 521 



General Relations 



The presence of Cambrian and early Ordovician sediments on the 

 northwest edge of the Piedmont Province of Pennsylvania and Maryland 

 has long been known, bnt it has not been heretofore suspected that 

 yoTinger Ordovician strata not only overlap . these early Paleozoic sedi- 

 ments, but also extend far southeastward onto the crystalline schists of 

 the Piedmont. 



The Piedmont upland of eastern Pennsylvania is traversed by a lime- 

 stone valley which extends southwestward from Schuylkill River, north 

 of Philadelphia, to Littlestown, near the Maryland State line. From the 

 Schuylkill to Quarryville it is narrow and is called Chester Valley. Be- 

 yond Quarry ville it expands northward into the wider Lancaster Valley 

 around Lancaster. West of the Susquehanna it again becomes narrow, 

 is known as the York-Hanover A^alley, and extends to Littlestown. The 

 valley is underlain by Paleozoic limestones. It is bordered on the north- 

 west in part by the overlapping Triassic sediments and in part by the 

 Cambrian arenaceous sediments of the Pigeon and Hellam Hills and of 

 Mine Ridge and North Valley Hills. It is bordered on the south by 

 overthrust Cambrian and Pre-Cambrian schists. Its southwest termina- 



1 Manuscript received by the Secretary of the Society February 15, 1923 

 Pviblislied with the permission of the Director of the U. S. Geological Survey and 

 the State geologists of Maryland and Tennsylvania. 



(507) 



