Bulletin of the Geological Society of America (1923) (14595339817)

Identifier: bulletinofgeolo341923geol (find matches)
Title: Bulletin of the Geological Society of America
Year: 1890 (1890s)
Authors: Geological Society of America
Subjects: Geology
Publisher: (New York : The Society)
Contributing Library: Smithsonian Institution Libraries
Digitizing Sponsor: Biodiversity Heritage Library

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
tends southwestward from Schuylkill River, northof Philadelphia, to Littlestown, near the Maryland State line. From theSchuylkill to Quarryville it is narrow and is called Chester Valley. Be-yond Quarryville it expands northward into the wider Lancaster Valleyaround Lancaster. West of the Susquehanna it again becomes narrow,is known as the York-Hanover A^alley, and extends to Littlestown. Thevalley is underlain by Paleozoic limestones. It is bordered on the north-west in part by the overlapping Triassic sediments and in part by theCambrian arenaceous sediments of the Pigeon and Hellam Hills and ofMine Ridge and North Valley Hills. It is bordered on the south byoverthrust Cambrian and Pre-Cambrian schists. Its southwest termina- 1 Manuscript received by the Secretary of the Society February 15, 1923Pviblislied with the permission of the Director of the U. S. Geological Survey andthe State geologists of Maryland and Tennsylvania. (507) 508 STOSE AXD JOXAS ORDOVICIAX IX PIEDMONT PROVINCE
Text Appearing After Image:
Cs GENEEAL RELATIONS 509 tion at Littlestown is due to the overlap of the limestone by the Triassicbeds. The Frederick Valley of Maryland is the sonthwestward con-tinuation of the York-Hanover Valley and is due to the emergence ofthe limestone from beneath the Triassic cover. The limestones exposed in the Hanover-York-Lancaster-Chester Valleywere until recently treated as a unit by workers in this area and werecalled the Shenandoah limestone. Detailed study by the writers, espe-cially in the vicinity of Lancaster, has resulted in the distinguishing ofseven limestone formations and one shale and the determination of theirage and relations. Seven of these formations are found in normal undis-turbed sequence northeast of Lancaster, as follows: Cocalico shale 1 Beekmantown limestone ( Conococlieague limestone Upper Cambrian. Elbrook limestone Middle Cambrian. Ledger dolomite ^ Kinzers formation L Lower Cambrian. Vintage dolomite I These correspond in part with the limestone formations tha

Note About Images

Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.