FORMATION OF COAL. I93 



are struck with the gradual passage, so to speak, of one class of 

 fuel into another: first, wood or peat into lignite, and then into 

 coal. This transformation is not apparent, but real ; in fact there is 

 not a shadow of a doubt that coal, jet, and probably graphite, 

 are the products of the metamorphoses of vegetable matter. This 

 explanation is supported by microscopical investigations which 

 reveal the actual wood structure. 



The era of the coal formation is called the carboniferous, but 

 seams are met with and worked in other formations. Mr. 

 F. R. Mallet has* described a seam between the Tertiary Sand- 

 stones and schists of Sikkhim Himalayas. 



The coaliield of Brora, in Scotland, is Oolitic, and was first 

 worked in 1598. 



It is, however, chiefly to the coal of the carboniferous period 

 that 1 purpose to devote this paper. 



Countless ages ago as was that time, the sun shone then as now ; 

 and was the means of giving to coal plants the carbon with which 

 their structure is built up. This process is still going on, and takes 

 place thus : — 



Carbonic acid gas is constantly being supplied to the atmosphere 

 in many ways : it is absorbed by plants,[and when the rays of the 

 sun strike them, it is decomposed mto its constituent parts — oxygen 

 and carbon, the latter being retained to enlarge the bulk of 

 vegetation, while the former is returned to the atmosphere. In 

 this way the sun imparts power : we burn wood and coal as fuel, 

 in so doing, the carbon again unites with the oxygen from which 

 it has been separated, (in the case of coal after millions of years of 

 separation) with such force, that for every pound of carbon under- 

 going complete combustion, an amount of mechanical energy is set 

 at liberty, equal to the raising of a 1 1,000,000 pound weight one 

 foot high 



The Flora. Of what kind was the flora of the Carboniferous 



* Records of the Geological Survey of India, Vol. VII. Part 2, page 53. 



