Pennsylvanian rocks are the principal coal-bearing formations and consist of cyclic sequences of sandstone, shale, conglomerate, clay, coal, and minor limestone.
(Pennsylvanian rocks; are; the principal coal-bearing formations) (Pennsylvanian rocks; consist; of cyclic sequences of sandstone, shale, conglomerate, clay, coal, and minor limestone)
Pennsylvanian rocks Pennsylvanian rocks
are consist
the principal coal-bearing formations
of cyclic sequences of sandstone, shale, conglomerate, clay, coal, and minor limestone