v.] ON THE FORMATION OF COAL. 107 



actual coal is there any reason why we should believe 

 it may not have taken 240 times as long to form ? I 

 know of none. But, in this case, the time which the_ 

 coal-field represents would be 25,000 x 240 6,000,000^ 

 years. As affording a definite chronology, of course such 

 calculations as these are of no value ; but they have much 

 use in fixing one's attention upon a possible minimum. 

 A man may be puzzled if he is asked how long Rome 

 took a-building ; but he is proverbially safe if he affirms 

 it not to have been built in a day ; and our geological 

 calculations are all, at present, pretty much on that 

 footing. 



A second consideration which the study of the coal 

 brings prominently before the mind of anyone who is 

 familiar with palaeontology is, that the coal Flora, viewed 

 in relation to the enormous period of time which it lasted, 

 and to the still vaster period which has elapsed since it 

 flourished, underwent little change while it endured, and 

 in its peculiar characters, differs strangely little from that 

 which at present exists. 



The same species of plants are to be met with through- 

 out the whole thickness of a coal-field, and the youngest 

 are not sensibly different from the oldest. But more than 

 this. Notwithstanding that the carboniferous period is 

 separated from us by more than the whole time repre- 

 sented by the secondary and tertiary formations, the 

 great types of vegetation were as distinct then as now. 

 The structure of the modern club-moss furnishes a com- 

 plete explanation of the fossil remains of the Lepido- 

 dendra, and the fronds of some of the ancient ferns are 

 hard to distinguish from existing ones. At the same 

 time, it must be remembered, that there is nowhere in 

 the world, at present, any forest which bears more than a 

 rough analogy with a coal-forest. The types may remain, 

 but the details of their form, their relative proportions, 



