e STRATIGRAPHICAL ORDER. | 11 
Upper Mercer Limestone and Ore. 
Upper Mercer Coal. 
Lower Mercer Limestone and Ore. 
Lower Mercer Coal. 
Connoquenessing Sandstone (upper). 
Quakertown Coal and Shales. 
Connoquenessing Sandstone (lower). 
Sharon Coal and Shales. 
Sharon Conglomerate. 
E> $9 Sf SX ge SY es ge 
It will be remembered that this series has been brought directly 
up to the Ohio boundary. It has even been followed across the 
boundary by the geologists of the Pennsylvania survey for the purpose 
of comparing the formations of some of the border counties of the two 
States. It belongs in all respects as much to Hastern Ohio as to 
Western Pennsylvania. | 
The purpose of the present chapter is to trace this series from the 
Pennsylvania line westward and southward through the State, and thus 
to secure as firm ground for the identification and correlation of the 
several elements of economic value which it contains as the present state 
of our knowledge will allow. 
The series cannot of course be followed asa whole. The natural 
sections which occur seldom exceed 300 feet in vertical range, and for 
the most part we are confined to much shorter sections, but there are 
several elements in the series so well characterized, that they can be 
identified with comparative ease and certainty wherever they are found. 
In addition to these single elements, there are some distinct groups 
of strata, including several of these well-marked and characteristic beds, 
and acquaintance with these groups may be made to greatly facilitate 
the work of tracing and identifying the series. The occurrence of a 
single stratum of the character referred to above is often enough to 
warrant the positive determination of the whole section in which if is 
found, but when one of these well-marked groups occurs, it “‘ makes as- 
surance doubly sure.” 
The single elements of the series upon which all men who have had 
occasion to study the Lower Coal Measures in either a scientific or a 
practical interest, have learned to rely with the greatest confidence, are 
the Limestones. The aggregate thickness of these limestones of the 
Lower Coal Measures is small; the thickness of the individual beds 
seems Insignificant when compared with that of the strata that accom- 
