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 

 gradation 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 Coniferse 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 tlwough 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 



