It has long been known that a bituminous coal seam is not a homogeneous bed, but is made up of a number of parallel bands. For example, Karsten in 1826 observed and described three banded constituents of such a seam, viz. Faserkohle, Matt Coal, and Glanz Coal, corresponding respectively to mineral charcoal, dull coal, and bright coal, and he gave some chemical details of their composition. Bowman, 1841, stated “there is a peculiarity in the texture of coal which has not received the attention it deserves. If it be clearly examined it will be found to consist of a series of parallel horizontal layers varying in thickness, these laminæ being best observed in the cross fracture, and often exhibit considerable difference in compactness and lustre. This structure, though in coal seams indistinct, is so general that it seems to point to some law which the chemical geologist might advantageously investigate.” Again, Wethered in 1884 observed that a coal seam is separated by partings into many beds differing in quality as in structure while in 1885 he pointed out the advisability of studying the different bands of a seam, and of recording details of its dull and bright portions.