USES OF THE FORMS OF CARBON 



111 



(Fig. 90) were probably formed from vegetable matter, 

 such as leaves, boughs, trunks, and roots, that collected 



FIG. 90. 



Parallel Seams of Coal Outcropping on a Hillside. Clay beds lie under the coal. Here the 

 other rock is sandstone ; often it is limestone as well. After Hopkins. 



under water in past ages. This material was prevented 

 from decaying by deposits of sand and mud, which kept 

 out the air (cf. 38) while the change to coal was going 

 on. In some imperfect coals the markings of the original 

 wood can still be seen. In "soft," or bituminous, coals 

 the change is usually more complete, but many carbon 

 compounds still remain; while in anthracite, or "hard," 

 coal the change of 

 vegetable matter to 

 coal is so complete 

 that very little is 

 present besides car- 

 bon. See Fig. 91. 



119. Uses of the 

 Forms of Carbon. 

 The element carbon 

 is put to a multitude 



FIG. 91. 



Coal Produced Yearly in the United States. Average 



by 10-year periods. Courtesy of Dr. 



F. W. De Wolf. 



