(2) Coal-formation Sub-Flora:
The Middle or Productive Coal-formation, containing all the beds of coal which are mined in Nova Scotia and Cape Breton, is the headquarters of the Carboniferous flora. From this formation I have catalogued[FM] one hundred and thirty-five species of plants; but, as several of these are founded on imperfect specimens, the number of actual species may be estimated at one hundred and twenty. Of these more than one half are species common to Europe and America. No less than nineteen species are Sigillariæ, and about the same number are Lepidodendra. About fifty are ferns and thirteen are Calamites, Asterophyllites, and Sphenophylla. The great abundance and number of species of Sigillariæ, Lepidodendra, and ferns are characteristic of this sub-flora; and among the ferns certain species of Neuropteris, Pecopteris, Alethopteris, and Sphenopteris greatly preponderate.
[FM] “Acadian Geology,” and “Report on Flora of Lower Carboniferous,” 1873.
These beds are the equivalents of the Middle Coal-measures, or Productive Coal-measures of Pennsylvania, Ohio, &c., and of the coal-formation proper of various European countries. Very many of the species are common to Nova Scotia and Pennsylvania; but in proceeding westward the number of identical species seems to diminish.
(3) The Millstone Grit Sub-Flora:
In this formation the abundance of plants and the number of species are greatly diminished.[FN] Trunks of coniferous trees of the species Dadoxylon Acadianum, having wide wood-cells with three or more series of discs and complex medullary rays, become characteristic. Calamites undulatum is abundant and seems to replace C. Suckovii, though C. cannæformis and C. cistii continue. Sigillariæ become very rare, and the species of Lepidodendron are few, and mostly those with large leaf-bases. Lepidophloios still continues, and Cordaites abounds in some beds. The ferns are greatly reduced, though a few characteristic coal-formation species occur, and the genus Cardiopteris appears. Beds of coal are rare in this formation; but where they occur there is in connection with them a remarkable anticipation of the rich coal-formation flora, which would thus seem to have existed locally in the Millstone Grit period, but to have found itself limited by generally unfavorable conditions. In America, as in Europe, it is in the north that this earlier development of the coal-flora occurs, while in the south there is a lingering of old forms in the newer beds. In Newfoundland and Cape Breton, for instance, as well as in Scotland, productive coal-beds and a greater variety of species of plants occur in this formation.
[FN] “Report on Fossil Plants of the Lower Carboniferous and Millstone Grit of Canada,” 1873.
The following would appear to be the equivalents of this formation, in flora and geological position:
1. The Seral Conglomerate of Rogers in Pennsylvania, &c.