90 PEOF. T. KTJPEET JONES — ON COiJ,. 



lime. Then again there are flakes and slabs of stone, which 

 is commonly called " slate," but is not slate; it is hard mud-stone 

 or shale, either in the coal itself, or from the strata close to it. 

 Coal that has much mud in it is sometimes passed off as smokeless 

 coal. Of course there is not so much smoke, because there is not 

 so much coal in it to give off smoke. There are, however, other 

 real smokeless coals. 



When coal is burned, ashes remain — not merely cinders, which, 

 like coke, are mostly the carbon of partially consumed coal ; and if 

 the ash, whether white or red, be examined under the microscope, 

 some of it shows the siliceous tissue of plants, and the other part 

 consists of atoms of mud and sand. 



Very much of the substance of some coal-beds consists of minute 

 spores that have been traced to the great Lycopods, Lepidodendron 

 and SigiUaria, which are allied to the Club-mosses, Isoetes and 

 Selaginella, and these spores were probably shed periodically in 

 enormous quantities. 



Great advances have been made by Dr. "W. C. Williamson in the 

 knowledge of the Lycopodiaceous trees of the coal, which he shows 

 to have partaken of the Exogenous structure of modern trees. The 

 well-known ribbed and jointed Calamites of the coal, represented 

 in the living world by the lowly JEquisetum, supplied their stems, 

 leaves, and spore-cases to the material of the coal. 



Sir William Dawson thinks that the tuberin of cork, of epidermis 

 in general, and of spore -cases in particular, is a substance so rich 

 in carbon that it is very near to coal, and so indestructible and 

 impermeable to water that it has contributed more largely than 

 anything else to the mineral. Prof. Prestwich refers to these, and 

 especially to gums and resins, as main constituents of the coal ; 

 and argues that, at the time of its formation, the climate was 

 warm and moist, with a larger percentage of carbonic acid than 

 exists at the present day, and a more rapid plant- growth.* 



In the accumulated deposits of sandstones, shales, and clays 

 interstratificd with the coal-seams, the fossils are such as the local 

 conditions would account for. Large Coniferous trees (like the 

 well-known examples found in Cragleith and other quarries) must 

 have been floated down by the rivers from the high gi'ounds of the 

 neighbouring regions. The numerous fronds of Ferns in the shales 

 were flooded off from lower heights and flats near by, together 

 with trunks and fragments of the Lycopodiaceous trees. Some of 

 this debris sank, waterlogged, in the lagoons and shallow land- 

 locked sea-water ; and the resulting black, stinking, carbonaceous 

 mud was the burial place of Molluscs, such as Anthracosia 

 and Anthracomya, of numerous Fishes, often of large size, as 

 MegaUchthys and Bhizodus, and Batrachian or Salamandroid 

 animals, as Anthracosaurus and Loxomma, with Annelids, Insects, 

 Scorpions, Water-spiders, King-crabs, etc., often enveloped in 

 special nodules, and other animals [JPtipa, Dendrepeton, etc.) 

 entrapped in hollow trunks of trees. 



* 'Geology,' vol. ii, 1888, pp. 117-120. 



