190 PROFESSOR BALFOUR ON CERTAIN VEGETABLE ORGANISMS 
to be the ends of woody coniferous tubes, are not so, but simply sections across 
cavities or spaces containing orange or yellow matter;—the depth of colour de- 
pending on the thickness of the section. In many instances where yellow matter 
exists in coal, we find it formed in cavities of different sizes, and in the centre it 
is common to meet with dark-coloured carbonaceous matter. On a section, such 
cavities in many instances exhibit a rounded contour, with a dark spot in 
the centre. Rounded or elliptical bodies, having a cellular or spore-like aspect, 
and containing yellow matter, occur more or less in all illuminating coals, whether 
splint, cherry, or cannel. 
The quantity of yellow matter in coals varies much. It abounds in many 
good gas-giving coals, such as Boghead, Methil, and Capeldrae. Coal must be 
regarded as a rock, varying in its composition in different localities. There is a 
eradation in its structure and constitution in passing from anthracite to house- 
hold and parrot coals; and the limit between coal and what is called bituminous 
shale is by no means definite. Judging by microscopical and other characters, 
as well as by chemical analysis, there seems no reason for separating Boghead or 
Torbane, Capeldrae, Methil, and other brown parrot coals from the category of 
true coals. Careful analyses show that the products of all are the same, viz., ammo- 
niacal liquor, tar, naphtha, benzole, napthaline, grease-oil, paraffine, and pitch. 
Bitumen, or a matter soluble in naphtha, exists in very small quantity in coals, and 
is more abundant in English caking coals than in cannel coals. The quantity 
of inflammable matter, or rather of hydrogen, in coals seems to determine the 
quantity of fixed carbon. In such coals as Boghead the quantity of hydrogen 
is very large, and hence the complete nature of the combustion. 
In reviewing the plants which are concerned in the formation of coal, J. D. 
Hooker, in his paper, published in the Reports of the Geological Survey of Great 
Britain, remarks, that Coniferze are chiefly found in the sandstone; and their 
remains being exceedingly rare in the clays, shales, and ironstones, it may be con- 
cluded that they were never associated with the Sigillarias and other plants which 
abound in the coal seams, but that they flourished in the neighbourhood, and were 
at times transported to these localities. 
Mr Binney of Manchester gives an instance of an erect fossil conifer passing 
from the roof of one coal seam ¢hrough another one, and having deposited round 
it many feet of sandstone, followed by underclay, a bed of coal, shale, and other 
successive deposits. This is looked upon by some as a proof of the rapidity with 
which the coal-beds were formed, of the rapid decomposition of those plants which 
constituted the coal, in comparison with the coniferous wood, and of the probable 
soft-tissued nature of the plants which formed that deposit. 
In coal from Newbattle, I have seen a remarkable cellular structure contain- 
ing yellow matter, associated with the ordinary dense carbonaceous matter form- 
ing the darker portion of the coal. The specimen seems to show, that different 
