CONTENTS. 
Page. 
Introduction 9 
Commercial geography 9 
Stratigraphy 11 
General statement 11 
Surface rocks 11 
Carboniferous system 11 
Rocks above the Waynesburg coal (Dunkard group or Permian 
series) 11 
The group as a whole. „ 11 
Definition 11 
Character and thickness 12 
Division of the group 12 
Rocks above the Upper Washington limestone (Greene for- 
mation) 12 
Character 12 
Distribution 13 
Rocks between the top of the Upper Washington limestone 
and the top of the Waynesburg coal ( Washington formation) 14 
Character 14 
Distribution 15 
Pennsylvanian series 15 
Rocks between the top of the Waynesburg coal and the bot- 
tom of the Pittsburg coal ( Monongahela formation) 15 
Definition 15 
Character and thickness 15 
Distribution 18 
Rocks which do not outcrop 19 
General statement 19 
Sources of knowledge 19 
Thickness 19 
Datum horizon 20 
Carboniferous system 20 
Pennsylvanian series 20 
Rocks between the Pittsburg and Upper Freeport coals (Cone- 
maugh formation ) 20 
Definition 20 
Thickness 20 
Character 21 
Rocks between the top of the Upper Freeport coal and the 
top of the Pottsville sandstone ( Allegheny formation . ) 23 
Definition 23 
Thickness 24 
Character 24 
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