GEOLOGY. 229 



increase of the eight preceding years amounted to two and three- 

 fourths millions of tons. Let us inquire, then, what will be the dura- 

 tion of our coal-fields if this more moderate rate of increase be main- 

 tained. 



u By combining the knoAvn thickness of the various workable seams of 

 coal, and computing the area of the surface under which they lie, it is 

 easy to arrive at an estimate of the total quantity comprised in our 

 coal-bearing strata. Assuming 4,000 feet as the greatest depth at 

 which it will ever be possible to carry. on mining operations, and re- 

 jecting all seams of less than two feet in thickness, the entire quan- 

 tity of available coal existing in these islands has been calculated to 

 amount to about 80,000 millions of tons, which, at the present rate of 

 consumption, would be exhausted in 930 years, but, with a continued 

 yearly increase of two and three-fourths millions of tons, would only 

 last 212 years. It is clear that long before complete exhaustion takes 

 place, England will have ceased to be a coal-producing country on an 

 extensive scale. Other nations, and especially the United States of 

 America, which possess coal-fields thirty -seven times more extensive 

 than ours, will then be working more accessible beds at a smaller cost, 

 and will be able to displace the English coal from every market. The 

 question is, not how long our coal will endure before absolute exhaust- 

 ion is effected, but how long will those particular coal-seams last which 

 yield coal of a quality and at a price to enable this country to main- 

 tain her present supremacy in manufacturing industry. So far as this 

 particular district is concerned, it is generally admitted that 200 years 

 will be sufficient to exhaust the principal seams even at the present 

 rate of working. If the production should continue to increase, as it 

 is now doing, the duration of those seams will not reach half that pe- 

 riod. How the case may stand in other coal-mining districts I have not 

 the means of ascertaining ; but as the best and most accessible coal 

 will always be worked in preference to any other, I fear the same 

 rapid exhaustion of our most valuable seams is everywhere taking 

 place. Were we reaping the full advantage of all the coal we burnt, 

 no objection could be made to the largeness of the quantity, but we 

 are using it wastefully and extravagantly in all its applications. It is 

 probable that fully one-fourth of the entire quantity of coal raised 

 from our mines is used in the production of heat for motive power ; but 

 much as we are in the habit of admiring the powers of the steam-en- 

 gine, our present knowledge of the mechanical energy of heat shows 

 that we realize in that engine only a small part of the thermic effect 

 of the fuel. That a pound of coal should, in our best engines, produce 

 an effect equal to raising a weight of a million pounds a foot high is a 

 result which bears the character of the marvellous, and seems to defy 

 all further improvement. Yet the investigations of recent years have 

 demonstrated the fact that the mechanical energy resident in a pound 

 of coal, and liberated by its combustion, is capable of raising to the 

 same height ten times that weight. But although the power of our 

 most economical steam-engines has reached, or perhaps somewhat ex- 

 ceeded, the limit of a million pounds raised a foot high per pound of 

 coal, yet, if we take the average effect obtained from steam-engines of 

 the various constructions now in usp, we shall not be justified in assum- 

 ing it at more than one-third of that amount. It follows, therefore, 



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