ON COAL. 147 



structure. But this objection is forever set aside, whfin, in the third 

 place, we subject even the most structureless coal to microscopic 

 scrutiny. The distinguished American microscopist, Professor Bailey, 

 of West Point, has been able to detect the unmistakable evidences of 

 vegetable structure even in the hardest anthracite. In fact it may be 

 affirmed that there is no coal which, under careful examination, will 

 not reveal a vegetable structure. 



Again : All the stages of gradation between perfect wood and per- 

 fect coal may be traced with the greatest certainty. We find the first 

 stage of this process in the blackened semi-bituminized logs of our 

 peat bogs and deltas of the present epoch. The next stage we find in 

 the lignites or brown coal of the tertiary period ; the next the highly 

 bituminous coal of the oolite ; then the coals of the true carboniferous ; 

 and lastly, the anthracites of the same and lower strata. Thus we 

 may trace the whole embryology of coal from its immature to its most 

 perfect condition — may trace and identify all the intermediate links 

 of the chain of conditions of which wood and coal form the extreme 

 limits. But not only in external form and appearance, but also in 

 chemical composition we can trace these several stages. Wood con- 

 sists of carbon, hydrogen, and oxygen ; coal consists of the same ele- 

 ments but in different proportions. In coal the proportion of carbon 

 is greater and of oxygen and hydrogen less than in wood. Now, if 

 we compare the chemical composition of wood, peat, lignite, bitumin- 

 ous coal and anthracite, we find a progressive decrease in the propor- 

 tion of oxygen and hydrogen, until, in anthracite, we find the carbon 

 almost pure, and absolutely pure in graphite, if we acknowledge this 

 as of similar origin. This chemical evidence is, it seems to me, abso- 

 lutely demonstrative. 



Lastly, direct experiment proves that peat, which we know to be 

 of vegetable origin, may, by strong pressure, be made to assume the 

 hardness, the density, the general appearance, and all the useful pro- 

 perties of coal. 



Assuming, then, the vegetable origin of coal as a basis of argu- 

 ment, we will proceed to speak of, and to account for, the principal 

 varieties of coal. 



All coal consists of two parts, the one combustible the other in- 

 combustible. It is easy to separate these from one another. If a 

 piece of coal is thrown into the fire the combustible portion passes 

 away in the form of gases, the incombustible remains behind in the 

 form of ash. Now, the relative proportion of these two vary infi- 

 nitely in different coals. We have every stage of gradation between 

 pure shale and pure coal, between pure incombustible and almost as 

 pure combustible. In the purest coal the amount of ash is only 1 to 

 2 per cent.; others, more impure, contain 5, 10, 20, 50 per cent, of 

 ash. At this point coal loses the property of ready combustion, and 

 with it loses also the name of coal in popular language. Bat the 

 geologist recognizes no remarkable change at this particular point — 

 no scientific reason why the name should change from coal to shale, 

 as there is no corresponding change of nature. From this point, 

 under the name of shaly coal, black slate, &c., the amount of ash. 

 may continue to increase and the amount of combustible matter to 



