PENNSYLVANIA. 



93 



Pennsylvania, 



BY PROFESSOR J. P. LESLEY, THE STATE GEOLOGIST. 



List of the Geological Formations of Pennsylvania. 



NOTES ON THE TABLE OF FORMATIONS. All beneath the Potsdam is styled Azoic, because no 

 survey has yet sufficiently differentiated the mass into its several systems. The term Eozoic is 

 rejected partly because both too vague and too shifting, and partly because it would suit the Cam- 

 brian system better than the Huronian and Laurentian, both of which remain to all intents and 

 purposes Azoic. The terms Huronian and Laurentian are known to apply lithologically to rock 

 masses in Pennsylyania, but their geographical relationships in the State are but imperfectly made 

 out. 



Much uncertainty still exists about the lines of demarcation between some of the formations 

 in Pennsylvania, such as between the Catskill and Chemung ; the Lower Helderberg and Clinton ; 

 the Hudson River and Utica; the Calciferous and Potsdam. 



Niagara, Onondaga or Salina, Corniferous and other names are omitted because of their un- 

 certain presence in many districts of the State; and because of the narrowness of their upturned 

 outcrops where they do exist. 



Some of the places named in the following lists occupy positions covering the width of two or 

 more steeply outcropping formations, to any one of which therefore they might be assigned. 



In the northern and western counties it is often impossible to say precisely whether places 

 stand upon Chemung, Catskill, Pocono or Mauch Chunk rocks. In such cases, Chemung has been 

 preferred, because the others might be studied in the surrounding hills on account of the general 

 horizontality of the bedding. J. P. L. 



