Geological Society. 303 



heat before any change is effected in the other constituents of the 

 coal. The number and appearance of these cells vary with each 

 variety of coal. In caking coal, the cells are comparatively few, and 

 those which do exist are highly elongated. Their original form the 

 author believes to have been circular j and he attributes their present 

 figure to the distention of gas confined in a somewhat yielding mate- 

 rial, subject to perpendicular pressure. In the finest portions of this 

 coal, where the crystalline structure, as indicated by the rhomboidal 

 form of its fragments, is most developed, the cells are completely 

 obliterated. In such parts the texture is uniform and compact : the 

 crystalline arrangement indicates a more perfect union of the consti- 

 tuents, and a more entire destruction of the original texture of the 

 plant. 



The slate-coal, or the third variety above mentioned, contains two 

 kinds of cells, both of which are filled with yellow bituminous matter. 

 One kind is that already noticed in caking coal; while the other kind 

 of cells constitutes groups of smaller cells of an elongated circular 

 figure. 



In those varieties which go under the name of Cannel, Parrot, and 

 Splent Coal, the crystalline structure, so conspicuous in fine caking 

 coal, is wholly wanting, the first kind of cells are rarely seen, and the 

 whole surface displays an almost uniform series of the second class 

 of cells, filled with bituminous matter, and separated from each other 

 by thin fibrous divisions. 



After describing these appearances, and illustrating them by draw- 

 ings, the author proceeds to speculate on the origin of the cells in 

 Cannel coal. He considers it highly probable that they are derived 

 from the reticular texture of the parent plant, rounded and confused 

 by the enormous pressure to which the vegetable matter has been 

 subject. 



The author next states, that though the crystalline and uncrystal- 

 line, or, in other terms, perfectly and imperfectly developed, varieties 

 of coal generally occur in distinct strata, yet it is easy to find speci- 

 mens which in the compass of a single square inch contain both va- 

 rieties. From this fact, as also from the exact similarity of position 

 which they occupy in the mine, the differences in different varieties 

 of coal are ascribed to original difference in the plants from which 

 they were derived. 



The author next adverts to the escape of inflammable gas from 

 coal, and cites various interesting facts, principally from the authority 

 of Sir H. Davy and Mr. Buddie, in proof of the existence of inflam- 

 mable gas ready formed in coal while contained in the mine ; of the 

 immense quantity which is sometimes emitted by blowers, indicating 

 a free communication between the reservoirs in which it resides ; and 

 of the great pressure to which it is there subject. He ingeniously 

 shows the probability of the gas existing within the coal in so com- 

 pressed a state as to be liquid. A consideration of these circumstances 

 induced the author, while engaged in his microscopic inquiries, to 

 search for a structure in coal capable of containing gas ; and he 

 accordingly discovered a system of cells, different from any before 



