as compared ivith thai of the present day. 365 



arranging them provisionally into genera ; the word genus signify- 

 ing, not a natural group of species, but a set of organs : and being 

 synonymous in many cases with a shorter and more expressive Latin 

 word, long in use and better understood. As an example, the genera 

 Sti'obilites and Lepidostrobus may be cited, whose species are various 

 cones (strobili), in some cases of Lepidodendron, in others, possibly 

 of other plants, widely different ; even the order to which they be- 

 long being distinct from that including Lepidodendron. 



This arrangement of portions of specimens under various genera, 

 is highly detrimental to the progiess of systematic botany, but is not 

 equally disadvantageous to the geologist, whose object it is to deter- 

 mine the relationship of strata, by means of a comparison of their 

 contained species without so particular a reference to their affinities. 

 The identification of these, is always open to question, from the 

 errors into which the imperfection of the specimens necessarily leads. 

 Two specimens of one plant, the one more perfect than the other, are 

 frequently described as different ; this is eminently the case in the 

 Sigillarice, the markings upon the surface of whose bark differ from 

 those on the similar surface exposed by the removal of that bark, 

 while, in many specimens, it is exceedingly difficult to determine 

 whether the latter be present or not. The markings also vary ex- 

 tremely in different parts of the same trunk, insomuch, that frag- 

 ments which had been regarded as characteristic of six or eight sepa- 

 rate species, have been more recently found to belong to one, that 

 one presenting a surface equal to those six or eight fragments col- 

 lectively, whereon the supposed species- were founded. Again, as the 

 specific characters used in dividing this genus are drawn from what 

 are considered very unimportant features in recent plants, namely, 

 the scars left by the fallen leaves, it is evident, that several distinct 

 species may be merged into one, in the absence of other distinctions 

 beyond that solitary character which does not suffice to recognize 

 analogously-marked living vegetables. 



The last obstacle which demands a passing allusion, because tend- 

 ing to retard our knowledge of coal fossils, is, that they cannot be 

 investigated independently. Representing the earliest known flora, 

 the individuals composing it are, as might be expected, more unlike 

 those now living, than what any subsequent formation contains. The 

 succeeding beds present us with plants which occupy, in point of orga- 

 nization, as in date of creation, a middle position ; and it is in many 

 cases, through the investigation of these alone that a clue can be 

 gained to the relationship existing between the earliest known and 

 the now living vegetable forms. It is not so to an equal extent in 

 the animal kingdom. A knowledge of recent shells, for instance, can be 

 brought to bear upon those of the Silurian formation (independently of 

 any study of their allies in the more modern strata), far more effec- 

 tually than an equal acquaintance with living plants can, upon those 

 preserved in our coal-fields. Many and sufficiently obvious are the 

 VOL XLV. NO. Xt'. — OCTOBER 1848. 2 B 



