110 



IRONSTONE.—- ORIGIN OF COAL. 



improvements ; but it is only some kinds of coal that are proper for 

 the purpose. Inattention to this circumstance has frequently led 

 landed proprietors to great unprofitable expense. Finding ironstone 

 and coal in abundance upon their estates, they have constructed fur- 

 naces and other works at a considerable cost, and have discovered 

 too late that the coal, however suitable for domestic or other uses, 

 was unfit to make iron of a marketable quality. To make good iron 

 from the best ironstone, it is necessary that the coal should be as free 

 as possible from every substance with which sulphur is combined. 

 It should possess the property of forming a hard coke or cinder ; and 

 if it have the quality of cementing or caking, it is the more valuable, 

 as the small coal can then be used for the purpose of coking, which 

 is frequently wasted where it does not possess this quality. 



Different opinions have been formed respecting the origin of coal. 

 In the primary and transition mountains, a particular species of coal 

 occurs in small quantities, as before slated, which is extremely hard 

 and splendent, and burns without smoke or flame, and is called an- 

 thracite ; it resembles and appears to pass into, the mineral called 

 plumbago or graphite. Common coal also sometimes graduates into 

 plumbago. Plumbago and anthracite are so completely mineralized 

 as to present no indications of a vegetable origin ; but the slate, in 

 which anthracite is imbedded, sometimes contains impressions of 

 ferns, and the strata over common coal, abound in vegetable impres- 

 sions : the cortical part of the vegetable is frequently seen converted 

 into mineral coal. It is not often that vegetable impressions are 

 found in the coal itself ; but some of the regular coal beds in the 

 Dudley coal-field, of which 1 have specimens of considerable size 

 and thickness, are composed of distinct layers of vegetables, convert- 

 ed into true mineral coal ; but, when separated, preserving the dis- 

 tinct cortical impressions of plants throughout the whole thickness of 

 the coal. It is reasonable to believe, that all the coal beds in the 

 same field are also formed of vegetable m^atter, though the impres- 

 sions may be effaced, I have also a specimen of common coal from 

 Derbyshire, with different cortical impressions. Granting that com- 

 mon coal is originally derived from the decomposition of vegetables, 

 it may be fairly asked,-— from whence did the vegetable tribes origin- 

 ally derive the carbon, of which their solid parts are principally com- 

 posed? Carbon either previously existed in nature, or trees and 

 plants had the power of forming it from more simple elements. 

 Neither of these opinions is improbable, nor are they at variance 

 with each other. If carbon be a compound substance, of which 

 hydrogen is a constituent part, it may be formed by the process of 

 vegetation, or it may exist also in the mineral kingdom, independent 

 of organic productions. That carbon is an original constituent ele- 

 mentary part of the globe, can scarcely be doubted, when we con- 

 sider that, united with oxygenj it is an important constituent part of 

 all limestone mouiitain.5> composirig nearly one half, by weight, of 



