182 SUPPLEMENT ABY NOTES. 



VII. Coal. — The numerous fossil plants from the carboniferous strata that are figured in 

 this work, render it necessary to put the general reader in possession of a concise view of the 

 nature and mode of formation of those ancient accumulations of vegetable matter, which now 

 constitute the beds of mineral fuel termed coal. 



Although at the present time no one at all conversant with geology doubts the vegetable 

 origin of Coal, the period is not distant when many eminent philosophers were sceptical on this 

 point ; and the truth in this, as in most other questions In natural philosophy, was established 

 with difficulty. The experiments and observations of the late Dr. Macculloch mainly contributed 

 to solve the problem as to the vegetable origin of this substance; and that eminent geologist 

 successfully traced the transition of vegetable matter from peat-wood, brown coal, lignite, and jet, 

 to coal, anthracite, graphite, and plumbago. Nor must the important labours of Mr. Parkinson 

 in this field of research be forgotten. The first volume of the " Organic Remains of a former 

 World," which treats of vegetable fossils, contains much original and valuable information on the 

 transmutation of vegetable matter, by bituminous fermentation, into the various mineral substances 

 in which its original nature and structure are altogether changed and obliterated ; and that work 

 may still be consulted with advantage by the student. 



But though the vegetable origin of all coal will not admit of question, yet evidence of the 

 original structui-e of the plants or trees whence it was derived is not always attainable. The 

 most perfect coal seems to have undergone a complete liquefaction, and if any portions of the 

 vegetable tissue remain, they appear as if imbedded in a pure bituminous mass. The slaty coal 

 generally preserves traces of cellular or vascular tissue, and the spiral vessels and dotted cells of 

 coniferous trees may often be detected by the microscope. In many instances the cells are filled 

 with an amber-coloured resinous substance ; in others the organization is so well preserved, that 

 on the surface of a block of coal cracked by heat, the vascular tissue, and the dotted glands, may 

 be observed. Some beds of coal appear to be wholly composed of minute leaves or disintegrated 

 foliage ; for if a mass recently extracted from the mine be split asunder, the exposed surfaces are 

 found covered with delicate laminas of carbonized leaves and fibres matted together ; and flake 

 after flake may be peeled off through a thickness of many inches, and the same structure be 

 apparent. Rarely are any large trunks or branches observable in the beds of coal ; but the 

 general appearance of the cai'boniferous mass is that of an immense deposit of delicate foliage 

 shed and accumulated in a forest, and consohdated by great pressure while undergoing that 

 peculiar process by which vegetable matter is converted into carbon. 



The essential conditions for the transmutation of vegetable substances into coal, appear to be 

 the imbedding of large quantities of recent vegetables beneath deposits which shall exclude the 

 air, and prevent the escape of the gaseous elements when released by decomposition from their 

 organic combination ; hence, according as these conditions have been more or less perfectly 

 fulfilled, coal, jet, lignite, brown-coal, peat-wood, &c. will be the result. 



VIII. Fossil Corals. — The real nature even of recent Corals is in general so imperfectly 

 understood by the intelligent reader who has not paid especial attention to the department 

 of natural history which treats of the class of animated nature termed Zoophytes, that in 

 describing the Fossil Corals In my Wonders of Geology, I felt it necessary to devote one Lecture 

 to the consideration of Corals and Crinoldea, in order to afiord a popular exposition of the 

 structure and economy of these highly Interesting tribes of animal existence.' 



A very prevalent error regarding their nature Is, that the beautiful stony substances generally 

 ' See Wonders of Geology, vol. ii. Leet. yi. p. 588. 



