Miscellaneous. 



435 



present in the whole extent of the atmosphere. And when we con- 

 sider that this is but a portion of the carbonic acid removed, we may 

 reasonably conclude that the atmosphere contained, at the commence- 

 ment of the great carboniferous epoch, more than double the quantity 

 of carbonic acid which it does now. 



We have no grounds for affirming that there is a less vegetation 

 now than in early times. On the contrary, it is highly probable 

 that the vegetation now is much greater than that of former 

 periods ; but it is no less certain that the vegetation of former times 

 was vastly more luxuriant at given places. For the continents being 

 of smaller dimensions, more carbonic acid could be spared to sup- 

 port a luxuriant vegetation in a confined area. It is owing to this 

 great luxuriance of vegetation, within a limited district, that vegetable 

 remains were accumulated in such quantity as to defy even a remote 

 analogy at the present day. 



Without reference to geological epochs, I may here state in what 

 manner coal and lignites are produced. The two principal kinds of 

 coal are, the wood, or brown coal of Germany, and the stone, or mi- 

 neral coal so abundantly found in our own country. 



The wood coal, from its composition, has evidently been formed by 

 a regular decay of plants with limited access of air. Hence the hy- 

 drogen is still present, whilst the oxygen has disappeared along with 

 carbonic acid. Mineral coal, on the other hand, is distinguished from 

 wood coal by containing a very small portion of hydrogen. Wood 

 coal has been formed by the evolution of carbonic acid from the sub- 

 stance of the plants composing it; whilst mineral coal has been 

 formed from the expulsion of part of its elements in the form of 

 combustible oils. These oils may often be procured from the. coal 

 by distillation. Heat appears to have been the cause of the expul- 

 sion of these oils. A remarkable example occurs in a quarry within 

 a few miles of St. Andrews, between that town and Cupar. A ba- 

 saltic rock which, has penetrated through the carboniferous strata, 

 forms a hill in the locality alluded to ; this rock is thoroughly im- 

 pregnated with coal naphtha. At whatever part a fragment may be 

 broken off, the fresh surfaces are quite humid with an imprisoned 



That is, Manchester would consume the total amount we have supposed to exist in 1,391,304 

 years. Or supposing that there were in the world about 65,000 places consuming the same 

 amount of fuel as Manchester, the total amount of coal in the great carboniferous deposits 

 would be consumed in about twenty-one years. But this is obviously absurd, for we know 

 that there is a much greater supply than this. Hence our original empirical number, instead 

 of being above, must be much under the truth. 



