COAL 27 



shells, sponges have siliceous spicules, molluscs hard 

 shells, and the higher animals bones and teeth. These 

 things are of a very permanent nature, and would cer- 

 tainly be found in quantities in the coal had animals 

 formed it. Further, the peat of to-day, which collects 

 in thick compact masses of vegetable, shows how plants 

 may form a material consisting of carbonized remains. 



Fig. 15. — Part of a Coal Ball, showing the concentric bandings in it which are 

 characteristic of concretions 



By certain experiments in which peat was subjected to 

 pressure and heat, practically normal coal was made 

 from it. 



Still a further witness may be found in the structure 

 of the "coal balls " described in the last chapter. These 

 stony masses, lying in the pure coal, might well be con- 

 sidered as apart from it and bearing no relation to its 

 structure; but recent work has shown that they were 

 actually formed at the same time as the coal, developing 

 in its mass as mineral concretions round some of the 

 plants in the soft, saturated, peaty mass which was to be 

 hardened into coal later on.^ All "coal balls" do not 



' See note on p. 28. 



