produced different varieties ; heat, pressure, and chemical action 

 continued for ages, produced far greater changes in the quality of 

 Coal than could be effected from the differences in the character of 

 the flora of which the varieties were originally formed, and the 

 change was in proportion to the age ; hence the recent deposits of 

 Coal are least removed from the character of the vegetation com- 

 posing it, while the deeper we go, or the farther back we go in time 

 the nearer will the Coal deposits approach the anthracitic character, 

 the intermediate variety being bituminous. 



In Ireland we have the three varieties with gradations from one 

 into the other. The Coals of Kilkenny are anthracitic ; the Coals 

 of Leitrim, Tyrone, and Ballycastle are bituminous ; and the Ter- 

 tiary Lignites of Antrim retain their woody character. 



In the varieties of Coal, then, we have a gradation from bitumi- 

 nous Coal to Anthracite, on the one side, and to peat on the other ; 

 differences depending upon the absence or presence, more or less, 

 of bitumen, which may be considered as a modification of the 

 resinous and oily parts of vegetable matter. Where the bitumen 

 is in excess the Coal is known as Cannel or Parrot Coal ; where the 

 bitumen is separated from the carbon the resultant is Anthracite. 

 The change from one variety to another occurs frequently in the 

 same field where the bitumen is driven off by volcanic agency, 

 similar to the separation of gas and tar from coke in the process 

 of making gas from Coal ; Anthracite, too, has been formed by 

 artificial means. 



Lignite differs from the other variety of Coal in being simply a 

 fossil wood more or less mineralised ; it is generally of a dull brown 

 colour, hence called Brown Coal ; showing the fibres of the wood 

 without the glistening lustre of Coal. It is found in many forma- 

 tions, but chiefly in the rocks of the Tertiary age. 



Compared with the age of Coal, Lignite is quite a recent forma- 

 tion; the relative ages of geological formations can only be 

 measured by the thickness of rocks that occur between them, and 

 in this way we find that Coal is as much older than Lignite as the 

 time it has taken to accumulate a series of rocks some 10 or 12 

 thousand feet thick that are found between them. 



