90 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



castle. These are, i, Rich caking coal, which is the most abundant 

 and the best in quality; 2, Cannel or Parrott or Splint; 3, Slate coal, 

 consisting of the others in alternating layers so as to give a slaty 

 structure. Vegetable structures can be recognized in all ; but be- 

 sides this, all show cells filled with wine-colored material, so volatile 

 that it can be expelled by heat before any change takes place in the 

 other constituents. The caking coal contains very few and those are 

 elongated ; he supposed that originally they were circular and that 

 the changed form was due to pressure. The finest portions of the 

 coal, in which *' crystalline " structure is best developed, show no 

 cells ; the crystalline structure indicates a more nearly perfect union 

 of the constituents, a more nearly complete destruction of the original 

 plant texture. The Slate coal contains two kinds of cells, both filled 

 with bituminous material ; one kind is that seen in the caking coal, 

 but the other is in groups of smaller cells, elongate circular in form. 

 The first type occurs rarely in cannels and related coals, where the 

 whole surface of the section is covered with an almost uniform 

 series of cells of the second type, filled with the bituminous matter 

 and separated by thin fibrous divisions. He was led by these fea- 

 tures to believe that difference in coals is due to difference in the 

 original plants. Another type of cells, empty, seem to have contained 

 gas. It is clear that Hutton recognized a structureless portion of the 

 coal containing plant fragments, of which the texture is still recog- 

 nizable. He made no effort to explain the origin of the bituminous 

 material. 



Link"" found vegetable structures in all coals and recognized 

 that coal is made up of woody matter, usually much comminuted; 

 but in some the structure is loose like that of modern peats, while 

 others are dense like some denser peats of modern origin. Bailey in 

 1846 and Goeppert in 1848 described vegetable structures in coal. 

 Dawson's''^ first important publication bearing upon the subject was 

 in 1846 but his studies were continued for many years thereafter. 



^ H. Link, " Ueber den Ursprung der Steinkohlen und Braunkohlen 

 nach mikroscopischen Untersuchungen," Abh. k. Akad. Wiss., 1838, pp. 33-44. 



*^ J. W. Dawson, " Notices of some Fossils found in the Coal Formation 

 of Nova Scotia," Quart. Jouni. Geol. Soc, Vol. Ill, 1846, pp. 132-136; 

 " Acadian Geology," 2d ed., 1878, pp. 393. 



