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The question now comes what kind of vegetation formed coal. 
The popular belief has always been that coal is formed from 
large trees: let us consider on what this belief is based. There 
is, under each seam of coal, a bed of clay termed the underclay ; 
in this Stigmariz are found, it is therefore argued that they 
were the roots of the trees which formed the coal, and that the 
underclay represents the old land surface. 
Secondly, it is argued that we find fossil trees and other kinds 
of vegetation in the roof, which must be the same kind as 
formed the seam below. 
Again, pieces of the film which attached to these trees, have 
been prepared and examined under the microscope and called 
sections of coal. 
With regard to the first, the occurrence of Stigmaria in the 
underclay, there are other roots in this clay more numerous 
than Stigmaria, and we have found the latter as often in the roof 
as the floor, a foot or so over the coal, and some distance away from 
anything approaching coal above; a specimen so formed is in 
the Bristol Museum surrounded with Cordaites. We have seen 
in the case of the fireclays of the Red-ash house and gas coals 
of the lower series, that they contained Stigmaria, but there 
was no seam of coal above, not even a shale in some instances. 
With regard to the occurrence of trees over the coal. By 
referring to the section of the Two Foot Seam, it will be 
observed that the coal is followed by 6 inches of black Duns 
containing Cordaites, then 8 inches of shale with Cordaites, but 
still no large tree fossils, then comes eight feet of fine Duns in 
which we find Ulodendron Lindleyanwm, Lepidodendron Stern- 
bergu, Calamites ramosus, and Oordaites. The argument based 
on the fossils in the roof then, so far as the large trees are con- 
cerned, falls to the ground, because if the trees in the roof were 
such as formed the coal below, one would expect to find them 
immediately over, they should be, so to speak, contemporaneous: 
but this, as before remarked, never is so; the black Duns and 
shale must have occupied a considerable time in deposition 
and represent a considerable lapse of time between the actual 
coal vegetation and the deposition of the trees in the fine 
