discovered in Gristhorpe Bay, Yorkshire. 313 



Several of these ferns apparently range under well known 

 genera ; and one especially is characterized as a polypodium, by 

 its lines of round seeds along the back of the leaf, parallel to 

 the central vein or mid rib ; and another, as an equisetum, by 

 the spike of cryptogamous flowers, and verticillate leaves. 



Others, again, deficient in fructification, can only be guessed 

 at by the general habit ; and of such, we seem to detect exam- 

 pies of the genera of Asplenium, Scolopendrium, Isoetes, and 

 more abundantly of the Polypodium, comprising the Aspidium, 

 Cyathea and true Polypodium. The fact is, the genera of ferns 

 are sufficiently obscure and difficult to arrange, even in a recent 

 state ; but, when fossilized, nearly impossible satisfactorily so to 

 do, as species in a state of fructification are rarely to be met 

 with, and even then the involucre, upon which so much de- 

 pends, is, and must be, indistinguishable. Some specimens ap- 

 pear of species now unknown in Europe ; and of those, many ap- 

 pear to be varieties of the tree ferns, which constitute such nu- 

 merous and splendid ornaments of tropical forests. And there 

 can be little doubt but some of the luxuriant fronds, belonging 

 to this class, when detached from the parent stem, and found 

 thus petrified, may greatly mislead an observer ; and, by being 

 Regarded as separate plants, needlessly multiply the number of 

 species. These arborescent Alices must have been very abun- 

 dant, as numberless stems, of considerable magnitude, are to be 

 seen interspersed^ with the other small plants ; sometimes in- 

 deed so compressed, as to present nothing but a mere impres- 

 sion; but, occasionally, retaining a stalky rotundity, of which 

 the interior is converted into the enclosing stony matter, while 

 the cortical part is completely carbonized. ' • 



In the superior strata, which constitute these pseudo coal de- 

 posites, we observe, with only a few scattered exceptions, the re- 

 mains of the softer or herbaceous vegetables, as the Cycadea?, 

 Filices and Gramineae ; while, at greater depths, we find a dense 

 consolidated mass of vegetable matter in the true coal-fields : 

 From what cause can such wideviathtg difference arise ? Can, 

 indeed, the latter be the trunks, — the timber of the primaeval fo- 

 rest overwhelmed under that enormous pressure; and the for- 

 mer, the surrounding herbaceous plants, principally growing in 

 loose and marshy ground along the outskirts of these woods ? 



That difference of structure in the same vegetable may be 



