coal measures

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Geology A stratigraphic unit equivalent to the Pennsylvanian or Upper Carboniferous Periods.
2. n. Geology Strata of the Carboniferous Period usually containing coal deposits.

Century Dictionary and Cyclopedia

1. In geology, that portion of the Carboniferous series in which beds of coal are found. The coal-measures are sometimes several thousand feet in thickness, and consist, in addition to the coal itself, of many beds of clay, shale, and sandstone. See carboniferous.
2. In America and Great Britain a special significance attaches to this term in geological classification. In Pennsylvania the coal-measures are those strata which carry the productive coal-beds of Carboniferous age and all deposits intercalated between them, and they are divided into lower productive, lower barren, and upper productive measures. The coal-measures, with the millstone-grit at their base, constitute the upper division of the Carboniferous system. In Great Britain and on the Continent their relations are similar.

GNU Webster's 1913

1. n. (Geol.) A subdivision of the carboniferous formation, between the millstone grit below and the Permian formation above, and including nearly all the workable coal beds of the world.