THEORY OF COAL FORMATION. 5 



(Figure 11 is after the classification of Reward, Figs. 7 

 and 9 after Mitchell, the plants after Feistmantel, and the rest 

 after I)e Koninck). 



The two chief theories as to the formation of coal are : 

 (1) That the vegetable matter which went to form the coal 

 grew where it is now found. (2) That the vegetable matter 

 drifted to its present position. We must remember two im- 

 portant points when considering the formation of earlier coal 

 seams: (1) That the climatic conditions and configuration of 

 the earth's surface were different then to what they are now; 

 and (2) that vegetation had not reached the same high state of 

 organism that we have now-a-days. It is admitted that in some 

 cases coal has been formed by drift material, such as might be 

 floated down some gigantic river, but drift packs are of com- 

 paratively rare occurrence, and coal formed by them would 

 lireak up more readily than when compacted in situ. 



Fig. 6. Product us 

 brachvthaerus. 



Fig. 8. Chsenomya etheridgei. 



Observed facts fit in better with the idea that coal was 

 formed where the vegetation grew. We find roots of trees 

 firmly embedded in the under-clays of coal seams, and it is 

 easier to understand how thick seams were added to by growth, 

 rather than by accumulations of shifting rivers. Near Cathe- 

 rine Hill Bay jetty, the forms of stumps of large trees are to 

 be seen in situ oil the top of the 14ft. seam, the stems of which 

 pass a few inches into the conglomerate roof. Similar growths 

 are to be seen in other places where that portion found in the 

 seam has been absorbed into the coal, Avhile that in the roof 

 has been partly converted into chalcedony. The various 

 layers of coal and rock show that the coal basins became sub- 

 merged at intervals. We would expect to find coal due to drift- 

 wood more impure with sand and mud, than if it were formed in 

 situ, and the dimensions of the seams to be more irregular. 

 The margins of forest-covered swamps in the valley and 



