STRATIGRAPHICAL ORDER. 5 
The second of Rogers’s sub-divisions, viz., the Lower (productive) 
Coal Measures, has for its boundaries, as will be remembered, the 
Brookville coal and the Upper Freeport coal, both being included in 
the series. As understood by the geologists of the First Survey, it em- 
braced the following principal elements, viz. : 
Upper Freeport Coal (Coal E). 
Freeport Limestone. 
Lower Freeport Coal (Coal D). 
Freeport Sandstone. 
Kittanning Coal (Coal C). 
Buhrstone Ore. 
Ferriferous Limestone. 
Serub-grass Coal. 
Clarion Coal (Coal B). 
Brookville Coal (Coal A). 
(Geology of Pennsylvania, H. D. Rogers, vol. II, part I, pp. 475-6.) 
To the elucidation of this very important division, the Second 
Pennsylvania Survey has devoted a greut deal of labor, and while the 
order of arrangement given above has been abundantly confirmed, the 
series has been expanded by the introduction of several elements previ- 
ously unrecognized. There is not exact agreement among the excellent 
geologists that have been employed in the work as to the minute com- 
position of the group in all its parts, but any one of the general sections . 
that they have furnished will be found to cover the essential facts. The 
section represented in the following diagram, Fig. 2, is taken from Pro- 
fessor White’s Report on Lawrence county, Q 2, page 22. 
In confirmation and establishment of this general section, the fol- 
lowing diagram, Fig. 3, represents the actual section that is found at 
New Brighton, on the Beaver river. <A section obtained at Smith’s 
Ferry, near the Ohio line, is shown in Fig. 4. Both of these figures 
are taken from White’s Report on Beaver county, Second Pennsylvania 
Survey, Q, page 41. 
