192 
then existing, however large or small, might undergo, by 
natural gravity, the changes that, as I have before said, 
preserve whole forests in the different forms of coals for 
the use of future ages. Thus the vegetable, in this instance, 
could but allow of certain of its most volatile parts, which 
gave it bulk when living, to pass into the clay, at the same 
time admitting of others to help the change. In general, 
Carbon and Bitumen are the ingredients of the remains, 
though sometimes it is nearly the same with that of a 
common brown dead leaf. The process of carbonization 1s 
occasionally carried on above ground, as in some Fungi— 
see Agaricus Elephantinus, tab. 36, and aurantius, tab. 381, 
Eng. Fungi. Dead leaves often become carbonized aboye 
ground; but the most frequent form of Carbon above 
ground is organic, as in Spherie—see Eng. Fungi, tab. 
372, 373, and 374, &c. 
The observation that both sides of the impressions exhibit 
the same side of the leaf, is nearly correct. It seems that 
the front of the leaf is least liable to decomposition, and 
that the impression is opposite to it; the substance of the 
leaf, chiefly the front, remaining on the other half when 
it is detached. Only the inner side of the cortex, appa-. 
rently, is seen, and I do not know that any signs of the 
fructification, which should be on the edge or other part 
of the back, have ever been detected, either in the impres- 
sion or otherwise. The two upper figures seem to have 
been a Pteris, if we can guess by what remains. The right 
hand one is the concave impression, and the other the 
convex one that fitted it. The lower figure is a lobated fern, 
and is also, perhaps, a Péeris. It is lodged in rather irony 
clay, and has a coaly film in some parts, and small frag- 
ments of coal are among the squame. Some have much 
More coal on the leafy surface. Indeed the edges of some 
of my specimens have little hollows, and a margin of Car- 
bonate of Lime and Pyrites, where the fruit may perhaps’ 
haye been. 
