2 GEOLOGY OF OHIO. 
nitely fixed. The most uncertainty prevailed in regard to the lowest di- 
vision. A conglomerate formation is generally liable to abrupt changes 
in its composition, and this particular formation proves no exception to 
the rule. No easily distinguishable stratum could be found to serve for 
its lower boundary, and more or less confusion of thought is shown in 
regard to what the formation really included. | 
The Brookville coal was taken, according to Lesley, as the true 
base of the Lower Coal Measures, and the Upper Freeport coal for the 
upper limit of this division. 
The third group has for its base the top of the Upper Freeport 
coal, and for its summit the bottom of the Pittsburgh seam. 
The fourth division extends from the Pittsburgh coal to the 
Waynesburgh coal, including both. 
The fifth division takes in the various rock formations above the 
Waynesburen coal as they occur in Western Pennsylvania. 
The Seral Conglomerate was always distinctly recognized and de- 
scribed asa proper and normal member of the Coal Measures, shown to 
be so by its frequently “containing regular and even thick beds of coal, 
identical in composition with the seams of the generally productive 
overlying group.” The Sharon coal in particular was always placed 
beneath the Conglomerate, as the term was then understood, and sev- 
eral other seams were also counted as sub-conglomerate, or at least 
inter-conglomerate seams. 
The second Geological Survey of Pennsylvania, which is now in 
progress, has in the main confirmed and established these earlier sub- 
divisions of the coal measures. In particular, the constitution of the 
Seral Conglomerate of Rogers has been clearly worked out. ‘This has 
been shown to be a complex formation, consisting of three main sand- 
stone or conglomerate strata, the lowest of which, viz., the Sharon Con- 
glomerate, directly underlies the Sharon or lowest coal seam. The 
middle stratum, often split into two and sometimes holding a thin coal 
seam between the two ledges, is known in Pennsylvania as the Conno- 
quenessing sandstone, and in Ohio as the Massillon sandstone. Above 
this stratum occurs the well-marked horizon of the Lower and Upper 
Mercer Limestones. Each of these limestones is underlain by a coal 
seam, and each frequently bears an iron ore. Above the Mercer lime- 
stones is found the third and last of the sandstone strata already referred 
