114 FLORA OF SOUTHERN NEW YORK AND NEW ENGLAND. 



Their external characters are well defined and for this reason they will always be of 

 stratigraphic value wherever found, but the problem of their exact biologic affini- 

 ties remains to be solved. 



Finally, a word should be said in regard to the determinations of the coniferous 

 remains, all of which have been referred to well-known fossil or living genera and 

 most of them to well-known Cretaceous species, solely upon their external characters. 

 These remains consist of leaves, twigs, cones, and cone scales, often completely 

 dissociated one from the other and yet in many instances apparently belonging to 

 the same genus or species. The actual relationship between specimens, as implied 

 in the names, may therefore be not always correct, and on the other hand speci- 

 mens to which different generic or specific names have been applied may belong to 

 the same species, and in this connection a wide and interesting field for future 

 investigation is open, in the examination of the internal, structure of the specimens, 

 when these are sufficiently well preserved to be sectioned and studied under the 

 microscope. The lignites, which occur in great abundance at many horizons, also 

 offer unlimited material for the future investigator, and their identification would 

 undoubtedly throw a flood of light upon the genera which are represented in the 

 flora, and in many instances would undoubtedly assist in correctly identifying and 

 associating dismembered parts of species. 



It may also be remarked in connection with the gymnosperms that the number 

 of species described does not give a correct idea of the actual proportion of this class 

 of plants to the entire flora. It is probable that this proportion was considerably 

 greater than the number of species would imply, as quantities of unidentified mate- 

 rial are undoubtedly gymnospermous. A superficial examination of the lignites 

 alone proves this to be the case, and much of the macerated material which forms 

 layers in the clays, especially at Kreischerville, also belongs in the same class. 



In the following table is given the number of species in the insular flora opposite 

 each subdivision of the vegetable kingdom in which they belong: 



Systematic tabulation of the insular flora, showing number of species. 



Subdivisions. 



Pteridophy ta 



Filicales 



Gleicheniaceae 



Gleichenia . . . 



Cyatheacese 



Thyrsopteris 



Polypodiacese 



Onoclea.. 



Salviniales 



Marsiliacese 



Marsilea 



Sagenopteris 



Spermatophy ta 



Gymnospermse 



Cycadales 



Cycadacese 



Podozamites 



Number 



of 

 species. 



6 

 4 

 2 

 2 

 1 

 1 

 1 

 1 

 2 

 2 

 1 

 1 

 216 

 27 

 2 

 2 

 2 



Spermatophy ta— Continued. 

 Gymnospermse— Continued. 



Conif erales 



Gingkoaceae 



Czekanowskia 



Baiera 



Protophyllocladus 

 Pinaceae 



Dammara 



Pinus 



Cunninghamites . . 



Sequoia 



Brachyphyllum . . 



Widdringtonites. . 



Frenelopsis 



Moriconia 



Cyparissidium 



25 

 3 

 1 

 1 

 1 



22 

 3 

 1 

 1 

 8 

 1 

 3 

 1 

 1 

 1 



