82 THE MEDALS OF CREATION. Cuap. V. 
arises, not from the absence of trees, but from their exter- — 
nal forms having been obliterated. 
3. The Roof, or upper bed. This generally consists of 
slaty clay, abounding in leaves, trunks, stems, branches, and 
fruits, and contains layers and nodules of ironstone, inclos- 
ing leaves, insects, crustaceans, Wc. 
In some localities beds of fresh-water mussels, and in others 
of marine shells, are intercalated ; layers of shale, finely lami- 
nated clay, micaceous sand and grit, and pebbles of limestone, 
granite, sandstone, and other rocks, are often present. The 
most illustrative examples of the foliage of the carboni- 
ferous flora are found in this deposit, which appears to be an 
accumulation of drifted materials derived from other rocks, 
and promiscuously intermingled with the dense foliage and 
stems of a prostrate forest ; the whole having been trans- 
ported from a distance by a powerful current or flood. 
Thus we have, in the first place, spread uniformly over 
the bottom, and constituting the bed on which the coal 
reposes, a stratum of clay (Under-clay), composed of fine 
pulverulent materials, which may have once constituted the 
soil of a vast plain or savannah; the only remains found in 
it are the roots of gigantic trees (see Lign. 36); for such 
the stigmarize are now proved to have been, and not aquatic 
plants, as was formerly supposed (4d. p. 476). 
Secondly, a bituminous mass (Coal), composed of coni- 
ferous wood, gigantic ferns, club-mosses, &c.; occasionally 
with trunks of trees penetrating vertically through it. 
Thirdly, a deposit of drift or water-worn materials (the 
Roof), mixed with the foliage and stems of numerous species 
of terrestrial plants; the whole appearing to have been 
subjected to the action of currents. The first, or Under- 
clay, raay have been the natural soil, in which the stigmariz 
erew; the next,—the Coal,—the carbonized stems, and 
other remains of the trees to which the roots belonged: and 
the last, or uppermost, forming the roof of the coal, may 
