This corresponds to the Catskill and Chemung of the New York series, and to the Upper Devonian of Europe.
The flora of this formation, which consists mostly of sandstones, is not rich. Its most distinctive species on both sides of the Atlantic seem to be the ferns of the genus Archæopteris, along with species referred to the genus Cyclopteris, but which, in so far as their barren fronds are concerned, for the most part resemble Archæopteris.
The characteristic American species are Archæopteris Jacksoni, A. Rogersi, and A. Gaspiensis. Cyclopteris obtusa and C. (Platyphyllum) Brownii are also very characteristic species. In Europe, Archæopteris Hibernica is a prevalent species.
Leptophleum rhombicum and fragments of Psilophyton are also found in the Upper Erian. There is evidence of the existence of vast numbers of Rhizocarps in this period, in the deposits of spore-cases (Sporangites Huronensis) in the shales of Kettle Point, Lake Huron; and in deposits of similar character in Ohio and elsewhere in the West.
The Upper Erian flora is thus very distinct from that of the Lower Carboniferous, and the unconformable relation of the beds in the Northeast may perhaps indicate a considerable lapse of time. Still, even in localities where there appears to be a transition from the Carboniferous into the Devonian, as in the Western States and in Ireland, the characteristic flora of each formation may be distinguished, though, as already stated, there is apparently some mixture in the South.
(2) Middle Erian Sub-Flora:
Both in Canada and the United States that part of the great Erian system which may be regarded as its middle division, the Hamilton and Marcellus shales of New York, the Cordaites shales of St. John, New Brunswick, and the middle shales and sandstones of the Gaspé series, presents conditions more favourable to the abundant growth of land-plants than either the upper or lower member. In the St. John beds, in particular, there is a rich fern flora, comparable with that of the coal-formation, and numerous stipes of ferns and trunks of tree-ferns have been found in the Hamilton and Corniferous series in the West, as well as trunks of Dadoxylon. It is, however, distinguished by a prevalence of small and delicate species, and by such forms as Hymenophyllites and the smaller Sphenopterids, and also by some peculiar ferns, as Archæopteris and Megalopteris. In addition to ferns, it has small Lepidodendra, of which L. Gaspianum is the chief. Calamiteæ occur, Archæocalamites radiatus being the dominant species. This plant, which in Europe appears to reach up into the Lower Carboniferous, is so far strictly Erian in northeast America. Sigillariæ scarcely appear, but Cordaites is abundant, and the earliest known species of Dadoxylon appear, while the Psilophyton, so characteristic of the Lower Erian, still continues, and the remarkable aquatic plants of the genus Ptilophyton are locally abundant.
(3) Lower Erian Sub-Flora:
This belongs to the Lower Devonian sandstones and shales, and is best seen in that formation at Gaspé and the Bay des Chaleurs. It is equivalent to the Oriskany sandstone, so far as its animal fossils and mineral character are concerned. It is characterised by the absence of true ferns, Calamites and Sigillariæ, and by the presence of such forms as Psilophyton, Arthrostigma, Leptophleum, and Nematophyton. Lepidodendron Gaspianum and Leptophleum already occur, though not nearly so abundant as Psilophyton.
The Lower Erian plants have an antique and generalised aspect which would lead us to infer that they are near the beginning of the land-flora, or perhaps in part belong to the close of an earlier flora still in great part unknown and few indications of land-plants have been found earlier.