626 EEPOiiT— 1891. 



up hj water (a few inches may. have been enough) to undergo the advanced 

 chemical change causing a proportional increase of b^-drogen. The dead sticks and 

 stems projecting out of and above the water-covered peaty mass below would natu- 

 rally supply the decaying touchwood and charcoal now lying as described above. 



"Doubtless a progressive change in the elaboration of hydrocarbon soon took 

 place to some extent, even as it does in peat ; but probably it was not completed 

 in the compact coal until many layers of both vegetable and earthy matters had 

 been accumulated (the former in place, and the latter from inundations), and caused 

 some amount of pressure and consequent heat. 



As, under favourable circumstances, the bright coal can be seen to have been 

 made up of spores, leaves, branches, and stems of special trees and other plants, 

 the place of growth must have been a swampy forest or jungle, of enormous 

 extent, probably in a warm (perhaps sub-tropical') climate, to account for the 

 hundreds of square miles of continuous coal-seams. 



Much has been learnt from the broken and rotting ruins of a forest, standing 

 on an area of the coal-growth, having been here and there sealed up and preserved 

 in that original state, before hydrocarbonisation had proceeded far ; whilst the 

 rest of the fallen timber and accumulated relics passed into the state of bright 

 coal, and became almost indistinguishable as to its structure except under the 

 microscope after special manipulation. The ' coal-balls ' of Oldham, in Lancashire, 

 and the 'bullions' at South Owram, in Yorkshire, are calcareo-carbonaceous 

 nodules, having been formed by the infiltration of water carrying carbonate of 

 lime from the shells in an overlying shale down into the bed of woody fragments 

 and other bits of dead plants. The carbonate of lime there segregated from the 

 mass to certain centres, and preserved, in round nodules, the vegetable structures, 

 before they were quite decomposed, more or less distinct as they had fallen on the 

 forest floor. Hooker,. Binuey,AVilliamson, and others have elucidated much of the 

 botany of the coal from this source. 



In the Lower Carboniferous series at Pettycur Bay, Burntisland, in the Firth 

 of Forth, are some well-preserved relics of the materials which would otherwise 

 have been used to form a coal-seam (referred to )}y Williamson and Binney). In 

 this case volcanic material has been ejected into or through a peaty mass, and, 

 having removed by force some of the soft wet material, has been mixed up with it 

 and settled down as a hard stratum, with well-preserved fragments of wood and 

 other tissues, into which carbonate of lime was subsequently intiltered. (Oarruthers.) 



A third instance was discovered by Mr. Wiinsch, in 1865, in the Lower Car- 

 boniferous series on the north-eastern shore of the Isle of Arran, where numerous 

 plant-remains are well preserved in and under volcanic ashes. The strata are 

 alternate sandy shales, thin coal-seams, and peperino-like tuff. Numerous truncated 

 trees remain upright, rooted in the shale. Sigillaria, Lejndodendron, Lepidophloios, 

 and Halonia, besides Sphenopteris and other ferns, are present.^ 



Cannel, Sj-c. — Lender the name of 'cannel' are known some important varieties 

 of coal, useful for distillation and gas-making ; and certainly they differed in their 

 method of deposition both from ordinary coal and in some particulars among 

 themselves. They all appear to have been formed of vegetable matter that, having 

 been soaked and macerated to a black pulp, like the most rotten and semi-fluid 

 peat, in lakes, lagoons, or other limited water-areas, became homogeneous masses 

 of hydrocarbon,"with much still discernible vegetable tissue, and occasionally 

 with bones, teeth, and scales of fishes, and the low kind of reptiles called Amphibia. 

 Earthy matter was sometimes mixed with the cannel ; and occasionally so much 

 accumulated that the black mud graduated into carbonaceous shale. Light sub- 

 stances would also have been blown into the water by wind. According to the 

 relative abundance of yellow-reddish hydrocarbons and macrospores, or of amor- 

 phous black substance (carbon) and microspores, is the diflerence between black and 

 brown cannel. (Carpenter.) 



Elsewhere the condition and place of the cannel are such as to suggest that, 



' A great predominance of ferns and lycopods indicates moisture, equability of 

 temperature, and freedom from frost, rather than intense heat. (Lyell.) 

 * GeoL Maj., 1865, and Trans. Geol. Soc, Glasgow, 1882. 



