32 ANCIENT PLANTS 



lated in coal-forming masses, but the above four methods 

 will be found to cover the principal ways in which coal 

 has arisen. 



Coal, as we now know it, has a great variety of 

 qualities. The differences probably depend only to a 

 small extent on the varieties among the plants forming- 

 it, and are almost entirely due to the many later con- 

 ditions which have affected the coal after its original 

 formation. Some such conditions are the various up- 

 heavals and depressions to which the rocks containing 

 the coal have been subjected, the weight of the beds 

 lying over the coal seams, and the high temperatures to 

 which they may have been subjected when lying under 

 a considerable depth of later-deposited rocks. The influ- 

 ence on the coal of these and many other physical factors 

 has been enormous, but they are purely cosmical and 

 belong to the special realm of geological study, and so 

 cannot be considered in detail now. 



To return to our special subject, namely, the plants 

 themselves which are now preserved in the coal. Their 

 nature and appearance, their affinities and minute struc- 

 ture, can only be ascertained by a detailed study, to 

 which the following chapters will be devoted, though 

 in their limited space but an outline sketch of the sub- 

 ject can be drawn. 



It has been stated by some writers that in the Coal 

 Measure period plants were more numerous and luxuriant 

 than they ever were before or ever have been since. 

 This view could only have been brought forward by one 

 who was considering the geology of England alone, and 

 in any case there appears to be very little real evidence 

 for such a view. Certainly in Europe a large proportion 

 of the coal is of this age, and to supply the enormous 

 masses of vegetation it represents a great growth of 

 plants must have existed. But it is evident that just 

 at the Carboniferous period in what is now called Europe 

 the physical conditions of the land which roughly cor- 

 responded to the present Continent were such as favoured 



