1877.] "llO [Lesquereux. 



species wliicli have been considered in Europe as characteristic of the Moun- 

 tain Limestone of i he culm, we have in the sub-carboniferous of Alabama and 

 Virginia Alethopteris nervosa, A. muricntd, and Splienoptcris Hceninrjhivisii, 

 this as common in the shale of the Helena coal as Neuropteris Smithii. 

 These three species, however, ascend in the American coal measures to 

 above the Millstone grit, which, though a kind of geological delimitation, 

 as well traced here as in Europe, is not a very definite line of demarcation 

 between the vegetable groups. For, with few exceptions, the lower carbon- 

 iferous flora has still the types of the sub-carboniferous, merely modified, 

 and represented by an increased or diminished number of species. The ly- 

 copodlaceous are still more abundant ; and we have, especially in the lower 

 veins, immediately above the Millstone grit, the largest number of species 

 of Lepi.lodendron and Ulodendron. Stlgmnria and Sigillaria have gained 

 in predominance; and in the ferns, new species o^ Neuropteridm, especially 

 some large-leaved Neuropteris and Odontopteris, are seen for the first time. 

 The wide-ranged Alethopteris Serlii, and its analogous species A. lonch- 

 itica, are there also ; the first already seen in the sub-carboniferous, 

 the second a derivation of A. Helenm, of the same lower division. A. 

 Pennsylvanica and A. Sullivantii, may be counted too in the first coal 

 above the conglomerate, as prefiguring in their more important characters 

 those of the Callipteris, which comes later in order of time. For one species 

 of this last genus only is known in the lower carboniferous, and another 

 from the Cannelton coal, already somewhat high up in the measures. As the 

 largest number of the species of plants of the coal have been obtained from 

 the lower carboniferous, it would be possible to continue the enumeration 

 of the species which are considered as proper to it or as characteristic. But 

 subsequent researches may greatly reduce the number; for as yet few strata 

 bearing remains of plants have been discovered in the upper carboniferous. 

 This division may be limited from the base or from the top of the barren 

 measures underlying the Pittsburgh coal; for indeed we know as yet noth- 

 ing of the flora of these barren strata. In ascending from the Millstone grit, 

 after passing the two first coal beds above it, the vegetation is rapidly modi- 

 fied in its characters by the gradual disappearance of the Lycopodiaceous 

 types, and the increasing predominance of the ferns. The species of Sigil- 

 laria continue in about the same proportion ; Annularia, SpJienophyllum, 

 Asterophi/Uites, become more abundant. And while some of the generic di 

 visions of the ferns, like Alethopteris and the large-leaved Pecopteris, seem 

 to pass away; the group of the Gyathem, represented by Pecopteris arbores- 

 cens, P. oreopteridia, P. polymorpha, etc., become the more numerous, 

 and especially characterize the upper carboniferous. They mostly belong 

 to tree ferns, which, besides the extreme abundance of their pinnae in the 

 highest veins of Pennsylvania, have left, petrified in the sandstone of Ohio 

 and Vii'ginia a prodigious quantity of trunks representing whole forests. 

 With these there is no trace of L'pidoden'lron ; some Sigillaria are left. 

 The vegetable work! was at that period a world of ferns, mixed with the 

 Cordaites, a race of as vet undetermined relation, it seems, half lycopodia- 



