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XVIII. — On the Chemical Changes attending the Formation 

 of Coal, and on the relation of these Changes to the Phikh- 

 sophy of Gas-making. By John Leigh, Esq., M.R.C.S., 

 F.C.S. 



Read March 4, 1861. 



As the rocks, above and beneath which it is imbedded, are 

 the altered relics of the pre-existent mineral structures which, 

 in countless ages past, formed the surface of this globe's 

 crust; so is coal itself the altered relic of a vegetation 

 which flourished in tropical luxuriance ere man and his 

 congeners were called into existence. Some of the most 

 glorious forms of vegetation that enrich the scenery of the 

 south and east of this time's world, had then their ana- 

 logues in this our northern clime : lofty trees reared their 

 vast heights, lived out their time and fell, to be succeeded 

 by others, till vast beds of vegetable matter accumulated, 

 and with moss and fern formed wide morasses. Then 

 peaty beds ensued, the remnants of a floral past, until 

 the crust of earth gave way on which they rested ; when 

 ocean flowed where solid land had been, and fishes played 

 and left their scales and bones upon the ocean's tangled 

 vegetable bed; and rivers brought their sand and mud into 

 the stiller deep, and covered all this up; and time rolled 

 on, and rocks were formed above it, till earthquake's might 

 projected them aloft, and laid all dry again; and thus, at 

 last, the old world's plants now yield us light, and heat, and 

 power immeasurable. Shut out from the atmosphere, but 

 still, from their very depth, subjected to a temperature far 

 above the average heat of this clime, the entombed beds of 

 vegetable matter, screened from the more rapid agency of 



