394 VEGETATION OF THE CARBONIFEROUS PERIOD 



identical the similar fossils in the various strata exposed in one mine ; 

 and as different the plants from remote coal-fields. From recent ob- 

 servations, it appears that subsequent movements may have isolated 

 portions of what once formed a continuous bed of coal, characterized by 

 a uniform vegetation throughout, and that hence a slight dissimilarity 

 between the plants of each portion may be attributable to a difference 

 in the conditions to which it was exposed in each. On the other 

 hand, it must be borne in mind, that at the present day a change in 

 position is almost surely accompanied by a very considerable change 

 in vegetation. The labour of identification too is not confined to the 

 comparison of specimens, but includes the determination of their names 

 when previously described. This is often all but impossible, from the 

 nature of the specimens, and the difficulty of presenting them, in an 

 available form, without plates. Hence it happens, that the labour of 

 individual observers is overlooked. It is, perhaps, impossible to employ 

 similar materials to better purpose than has the author of the " Flore 

 Fossile " those upon which he laboured ; and yet the difficulty of 

 naming the species by that work is very great, and must be so ; for the 

 specimens to be compared are, like the originals, mere fragments, and 

 the genera of Ferns adopted are far from being properly defined, though 

 as judiciously as the materials would permit. On the contrary, many 

 of these are not supported by the examination of living analogues ; 

 whilst others are unavoidably founded on isolated portions of plants, 

 whose appearances whilst living and affinities are alike unknown, whether 

 amongst their contemporaries by which the world was then inhabited, 

 or those hitherto unrecognised allies that may now surround us. 



The foregoing remarks admit of illustration, to a certain extent, 

 by particular instances. This may be useful, because indicating to the 

 student those errors into which he is most liable to fall. Since, however, 

 he may not be aware how closely the course of investigation pursued 

 in the examination of a living Flora ought to be followed in studying a 

 fossil one, it is, perhaps, well to enumerate those steps by which a know- 

 ledge of both can be obtained. 



As a field for botanical research there is none so novel as the coal 

 formation, the few yards of shaft being more than equivalent to the longest 

 voyage, in respect of the amount and kind of difference between the ve- 

 getation the naturalist is acquainted with and that he seeks to under- 

 stand. Whatever be the nature of the vegetation to which the botanist 

 is transported, he commences by observing: — 1. What are the orders, 

 genera, and species of plants characterising the Flora; their mutual 

 affinities, and their relations to those of other countries ; their numbers, 

 and the relative proportions which the natural groups under which they 

 arrange themselves, bear to each other. 2. The geographical distribu- 



