OF COAL. 455 
the cinders beneath our grates, traces of fossil 
plants, whose cavities, having been filled vrith 
silt, at the time of their deposition in the vege- 
table mass, that gave origin to the Coal, have 
left the impression of their forms upon clay and 
sand enclosed within them, sharp as those re- 
ceived by a cast from the interior of a mould. 
A still more decisive proof of the vegetable 
origin, even of the most perfect bituminous Coal 
has recently been discovered by Mr. Hutton ; 
he has ascertained that if any of the three va- 
rieties of Coal found near Newcastle be cut into 
very thin slices and submitted to the microscope, 
more or less of vegetable structure can be recog- 
nized.* 
* "In these varieties of coal," says Mr.- Hutton, '* even in 
samples taken indiscriminately, more or less of Vegetable Texture 
could always be discovered, thus affording the fullest evidence, if 
any such proof were wanting, of the Vegetable Origin of Coal. 
" Each of these three kinds of coal, besides the fine distinct 
reticulation of the original vegetable texture, exhibits other cells, 
which are filled with a light wine-yellow-coloured matter, appa- 
rently of a bituminous nature, and which is so volatile as to be 
entirely expelled by heat, before any change is effected in the 
other constituents of the coal. The number and appearance of 
these cells vary with each variety of coal. In caking coal, the 
cells are comparatively few, and are highly elongated. — In the 
finest portions of this coal, where the crystalline structure, as in- 
dicated by the rhomboidal form of its fragments, is most deve- 
loped, the cells are completely obliterated. 
" The slate-coal, contains two kinds of cells, both of which are 
filled with yellow bituminous matter. One kind is that already 
noticed in caking coal ; while the other kind of cells constitutes 
groups of smaller cells, of an elongated circular figure. 
