258 MR. JOHN LEIGH ON THE CHEMntCAL CHANGES 



in more rapid and unequal proportion, was this diminished in 

 the forming coal. It has been shown by the products of 

 the decomposition of vegetable matter and water, when air 

 is excluded, that the elements of the decaying matter divide 

 themselves amongst each other, so to speak, under these 

 circumstances, and pass off"; one in combination with a por- 

 tion of each of the rest, the proportion of the combination, 

 as will be shown hereafter, varying with the temperature. 

 In the earlier periods of decomposition and entombment, 

 the carbonic acid evolved would be large, relatively to the 

 carburetted hydrogen and water ; but as the process went on, 

 and the oxygen became diminished in the decomposing 

 matter, these proportions would become reversed, till scarcely 

 any thing but carburetted hydrogen would be at length given 

 off by the coal, and this even would finally cease on its con- 

 version into anthracite. Let us see how far analysis w^ill 

 carry out this reasoning. There is no reason for believing, 

 however much the external form, and perhaps internal me- 

 chanical structure, of the Flora of the ancient world may 

 have differed from that of the present, that the composition 

 of the woody fibre of that remote period differed in any 

 material degree from its composition now. Prodigal as 

 nature is in shapes, and forms, and hues; unsparingly as ar- 

 rangements have been varied — the Almighty hand thatguides 

 her operations works with the simplest means, and the most 

 unchanging processes. His power displays itself in the in- 

 finite variety accomplished with the most limited materials. 

 It is reasonable to suppose, it is in accordance with all know- 

 ledge of the subject, that the same formula that represents 

 the composition of woody matter now, would exactly corre- 

 spond with, or closely approximate to, that representing its 

 composition in the vegetation of a past world. We have 

 seen before, that the general formula for woody fibre now 

 may be represented by Cgg H^j O^j. An analysis of the 

 cannel coal of Lancashire, and of the splint coal of New- 



