STRATIGRAPHICAL ORDER. 121 
stone) is quite a constant element. The coal is overlain by the second 
stratum of the great Mahoning sandstone, a much heavier and coarser 
ledge than the lower division which overlies the Upper Freeport coal. 
The upper sandstone is the Buffalo sandstone of White’s Report on 
Lawrence County, Pennsylvania. The thickness of the Mahoning sand- 
stone (lower) may be taken as 25 feet, and of the Buffalo sandstone or 
Upper, as 40 to 50 teet. ) 
The ores that help to mark the series and establish connections 
have been mainly omitted from this review, but they are better known 
in the furnace tracts than the coal seams, though less widely distributed 
through the field at large. 
The intervals between the leading elements of the scale are as 
follows : 
Cambridge limestone, in two strata, 10 to 20 feet apart. 
Interval (from Upper Cambridge)................ssccscsscee sossesseces 55 to 70 
Brush Creek coal—No. 7a. 
Brush Creek limestone—Upper Buff limestone. 
Iboyrereyenll (oxoren, 183, (Ob C@EM)))'565600000086800600000000600000060000 046058000000000 40 to 60 
Upper Freeport coal—No, 7, Waterloo seam. 
Upper Freeport limestone. 
intenvalaGinony Wey Hy COal) Rs... .cccs, csecesecsscsetcsscrsiecs stevedscsceases 30 to 50 
Lower Freeport coal—No. 6a, Hatcher seam. 
Lower Freeport limestone. 
Interval (from L. F. coal) ...... eee aes iuaeet ee cauiecedaee ais deossmecuneeanes 30 to 55 
Middle Kittanning coal—No. 6, Sheridan seam. 
Maa Gervaliersece soc sccsscslscas savece covscscerastssdh cote scisesdaedsshivececwescseses 25 to 45 
Lower Kittanning coal—No. 5, New Castle seam. 
MGerValesrwenet erodes cone teceseette secodcnoslcessCstendesscscccedses ted esesesioences 20 to 35 
Ferriferous limestone and ore. 
For the representation of the series from the Ferriferous limestone 
to the Cambridge limestone, inclusive of both, the general section pre- 
pared by E. McMillin, of Ironton, for the Ironton and Northeastern 
Railway Company, is hereby reproduced with the permission of the 
author. The names of the coal seams, as now understood, are inclosed 
in brackets, the only addition to the section. | 
This section jillustrates the wonderfully close agreement of this 
portion of the scale with the several fields that have already been passed 
in review. Rete: 
The series below the Ferriferous limestone is by no means as clear 
or as well understood as the series above, but there are many well-settled 
