ON THE FORMATION OF COAL 157 



ime which the coal-field represents would be 

 !5,000 X 240 = 6,000,000 years. As affording a 

 efinite chronology, of course such calculations as 

 hese are of no value ; but they have much use in 

 xing one's attention upon a possible minimum. 

 L man may be puzzled if he is asked how long 

 Lome took a-building ; but he is proverbially safe 

 he affirms it not to have been built in a day ; 

 rid our geological calculations are all, at present, 

 retty much on that footing. 



A second consideration which the study of the 

 3al brings prominently before the mind of any one 

 r ho is familiar with palaeontology is, that the 

 :>al Flora, viewed in relation to the enormous 

 eriod of time which it lasted, and to the still 

 aster period which has elapsed since it flourished, 

 nderwent little change while it endured, and in 

 is peculiar characters, differs strangely little from 

 iat which at present exist. 



The same species of plants are to be met with 

 iroughout the whole thickness of a coal-field, and 

 le youngest are not sensibly different from the 

 Idest. But more than this. Notwithstanding 

 aat the carboniferous period is separated from us 

 y more than the whole time represented by the 

 Bcondary and tertiary formations, the great types 

 f vegetation were as distinct then as now. The 

 Tucture of the modern club-moss furnishes a 

 Dmplete explanation of the fossil remains of the 

 ,epidodendra, and the fronds of some of the ancient 



