Some of these terms are used in composition to describe beds partaking of both characters, as—
Rock-binds,—sandy shale or shaly sandstone.
Clunch-rock,—hard sandy clay, &c. &c. &c.
Corbonaceous Materials.—There ia every gradation from a mere carbonaceous shale or batt through a " slummy," smutty, or batty coal to a perfectly pure bright coal with but very slight admixture of earthy matter.
The coals are usually bituminous, that is, they still retain mingled with the carbon such a proportion of hydrogen and oxygen as would allow of bitumen being formed from them by distillation. Some of them, indeed, are cannel coal, which blazes almost like a candle, and consumes away so as to leave only a little light, white, powdery ash.
Usually, however, the coals are of the variety known as Cherry coal, (see Ronald's and Richardson's "Chemical Technology," vol. i, p. 45,) being got in large blocks, not caking, easily lighted, and burning with a clear, cheerful flame, leaving a white ash, and no very large proportion of cinders.
Ironstones.—The ironstones are all clay ironstone, occurring either in thin regular seams or in layers of nodules, balls, or concretions. The principal kinds have now been analyzed in great detail under the direction of Dr. Percy. (See "The Iron Ores of Great Britain," Part II.)
Usually in all local descriptions of the Coal-measures of South Stafford, whenever the word " stone" is used, ironstone must be understood.
Parting and pricking mean the thin layers between the more important beds; they are generally some variety of clay.
Grouping of the Measures.—The way in which the various beds of clay, shale, sandstone, coal, and ironstone are interstratified with each other, may be seen by reference to the four published sheets of Vertical Sections. Nos. 16, 17, 18, and 26. The Coal-measures of South Staffordshire, as of most other districts, are made up of a great series of alternating beds of these materials,— all of them varying in thickness and extent. As a general rule, the beds of coal are more constant in thickness, and extend over wider areas, than the beds of other materials. Next in constancy and persistency to the coals come the finest grained rocks, such as the batts, and the finer varieties of fire-clay and clunch. The sandstones and coarser grained rocks are most capricious in their occurrence, and vary most suddenly in thickness and character.
Beds of coal are not only constant in thickness over very considerable areas, but also generally in quality and character. This is so much the case, that colliers and other persons who have been long engaged in handling the coals of a district will recognize detached blocks of different coals lying loose on the pit bank, even when taken to a distance of some miles from their own pits. They will name the seam each block came from, when to
