POCOXO OF LESLEY ; VESPERTINE OF ROGERS 17 



Geological Survey of Pennsylvania for formations along the eastern out- 

 crop are : 



Lower Carboniferous (Mississippian) . . . j po^^on^^^^ 



( Catskill. 



Upper Devonian. < Chemung. 



( Hamilton. 



The Pocono of Lesley; Vespj:rtine of Rogers 

 distribution and characteristics of the rocks 



Nomenclature. — To the lower division of the Mississippian in Pennsyl- 

 vania, Professor H. D. Rogers applied the name Vespertine, which Avas 

 not accepted generall}'- by geologists. Many j^ears later Professor J. P. 

 Lesley offered instead the geographical name, as the formation had been 

 described by him as characteristically developed in the Pocono moun- 

 tains of eastern Pennsylvania. This term was used in the Pennsylvania 

 reports, and it has been adopted by the Maryland survey as well as by 

 some of the United States geologists. 



In the eastern part of the Appalachian basin, the Pocono, containing 

 many thick beds of hard rocks, is a notable mountain maker. It sur- 

 rounds the anthracite coal fields of Pennsylvania, the Broad Top coal 

 field of the same state, and a small outlier remains farther east in Fulton 

 county, almost on the edge of the Great valley ; the outcrop is prac- 

 tically continuous along the Alleghenies of Pennsylvania, and similarly 

 long outcrops are shown along the Alleghenies and other mountains in 

 Maryland and the Virginias. The character changes westwardl}^ along 

 the northern border, but the information now available renders recog- 

 nition of the varying conditions a matter of little difficulty. 



For knowledge of this formation along the northern and eastern ex- 

 posures in Pennsylvania geologists are indebted to Messrs J. F. Carll, 

 H. M. Chance, and C. A. Ashburner, but especially to Dr I. C. White, 

 whose reports cover by far the larger part of the area within which the 

 Pocono is shown. For this reason the writer prefers Doctor White's 

 measurements and determinations to his own, where the observations 

 overlap in that state, the more so because those by Doctor White are 

 later in date and are to be regarded as completing his study of the for- 

 mation in Pennsylvania. 



The region to be studied in review is so large that it must be described 

 in areas, the first being that in Pennsylvania and Maryland eastward 

 from the Allegheny plateau, which may be termed 



