In a former memoir* the writer described the Lower Carboniferous or Mississippian of the Appalachian basin. In this the effort will be to describe the lowest formation of the Coal Measures or Pennsylvanian of the same basin.

The Coal Measures were studied in detail first in the Virginias and Pennsylvania by Professors William B. and Henry D. Rogers, who divided them into five groups, numbered XII, XIII, XIV, XV, and XVI, and afterwards named

XVI. Upper barren group.

XV. Upper coal group.

XIV. Lower barren group.

XIII. Lower coal group.

XII. Seral conglomerate.

This grouping, based originally on somewhat arbitrary grounds, proved so convenient that it was accepted by most of those who have written on the northern portion of the Appalachian basin. In accordance with later usages, geographical terms were introduced by the Pennsylvania geologists. Those which have the priority are

Dunkard of I. C. White,

Monongahela of . . .

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