|SECOND GEOLOGICAL SURVEY OF PENNSYLVANIA - REPORT OF PROGRESS
P. DESCRIPTION OF THE COAL FLORA OF PENNSYLVANIA
AND OF THE
CARBONIFEROUS FORMATION THROUGHOUT THE UNITED STATES
BY LEO LESQUEREUX; ©1879
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©George Langford III, 2011
|On the origin, succession, and modifications of the vegetable types, from the base of the Coal Measures upwards.
57. Though the evidence is not admitted by all the
phytopalaeontologists as entirely satisfactory, it seems. proved that
the types of the primary divisions of the coal flora are represented
already in the upper, even from the middle of the Silurian.|
Remains of Calamariae have been described as Sphenophyllum primaevum,*
As yet, no remains of Ferns are known from the Silurian of this Continent; but Saporta has described and figured under the name of Eopteris Morieri,
Of the Lycopodiaceae, Prof. Dawson has found remains of Psilophyton and Selaginites in the Upper Silurian of Canada §
Of the Sigillarice, fragments of a stem is described and figured as Protostigma Sigillarioides from the Cincinnati group.*
Of the Cordaites, remains of Cordaites angustifolius are represented with descriptions by Prof. Dawson,*
In ascending the Series of the formations, the remains of land plants, all referable to the same divisions of the vegetable reign, become more numerous, also better preserved and more positively determined, so that, from the middle Devonian, Prof. Dawson already describes two species of Calamites, a Cyclopteris incerta, which, from the branch representing the fructification, is like a species of Archaeopteris; a Psilophiton, two species of Lepidodendron, a Sigillaria, a Didymophyllum, and three Cordaites.*
In the Catskill and the Chemung above, with species of Lepidodendron, Sigillaria, Calamites, and Cordaites, the Ferns are more abundantly represented by Archaeopteris species, a peculiar and distinct type which pass to Adiantites and Sphenopteris, soon losing its identity. For the last traces of Archaeopteris are seen in the middle of the Sub-conglomerate, or at the horizon of the Chester limestone.
It is at this horizon, or in the middle of the Sub-conglomerate, that appear two essential and more predominant and persistent types of the Neuropteris; the first in Neuropteris tenuifolia, Neuropteris Loschi; the second in Neuropteris hirsuta, which, both continued by identity and derivation, are abundantly distributed in the whole thickness of the Carboniferous, and higher up to the Permian.
Here also we find in their admirable luxuriance the Megalopteris, an isolated and peculiar type of Ferns, whose species, by the forking of the medial nerve of their leaves and by their venation, have left trace of their existence only in the more recent Neuropteris fasciculata. The type does not appear to be derived from a more ancient one. A species is quoted by Prof. Dawson in the Devonian of Canada; all those described in this flora are from the horizon mentioned above, that of the Chester limestone or the upper part of the Waverly group.
I have remarked already that it may be a representative of the land flora of the Carboniferous age. We have, indeed with it, plants which, without anteceding relatives are also limited in their distribution to the same formation: Lesleya grandis, one species of Orthogoniopteris, Danaeites macrophyllus, Protoblechnum Holdeni, Eremopteris marginata, Hymenophyllites Balantini, and a true Polypodium, not described by Prof. Andrews, but which, from the specimens examined (fragments of fruiting linear narrow leaves) could be admitted as representing one of the numerous varieties of the living Polypodium angustifolium Sw. of Cuba.
§ 58. The order of the Equisetaceae (quite as distinct at the beginning of the coal period as it is at our time) is limited to four types of characters very difficult to fix, and scarcely modifiable. Of the Equisetites the U.S. Coal flora has merely a few sheaths. Of the Calamariae, the Calamites are present in the lower Devonian as well as their branches, the Asterophyllites, and are distributed through the whole thickness of the coal measures ascending to the Permian. The same remark applies to Annularia. Sphenophyllum, more distinctly characterized, not merely as a genus, but in its different species, has a wide distribution. Present in the Silurian and the Devonian, it is in the Sub-carboniferous in three species, and after, by an abundance of its remains, it shows its passage through all the strata of the Coal-measures to the Permo-carboniferous, where it disappears entirely.
Bornia and Calamodendron are known as yet by mere fragments, their relation to the Calamariae, or to a higher order of plants is still unascertained.
§ 59. In the Ferns, the genus Neuropteris is the more remarkable by the elegance and size of its fronds and leaves. The type may be derived, as well as that of the Megalopteris and of the Archeopteris from the silurian Eopteris; but the genus itself is limited in its characters, which though variable, are always distinct. The group of the Cyclopterids and that of the Neuropteris proper are represented in the Devonian from which Prof. Dawson has described Cyclopteris varia and Neuropteris polymorpha allied to Neuropteris angustifolia. This last type especially has numerous representatives through the whole thickness of the coal measures in Neuropteris hirsuta, Neuropteris cordata, Neuropteris Loschii, Neuropteris tenuifolia, all species present in the Sub-conglomerate, most abundant in the upper Carboniferous, passing higher to the Permian. Neuropteris hirsuta and Neuropteris Loschii fill whole strata of soft sandstone or black shale at the horizon of the Pittsburgh and the Pomeroy coal. Neuropteris fimbriata and Neuropteris inflata have the same distribution from the Sub-conglomerate, but as yet have not been seen above the Carboniferous.
The species mentioned above represent the section of the thin veined Neuropteris; a sub-division of the same group, that of the coarse veined species, includes Neuropteris Clarksoni, Neuropteris Desorii, Neuropteris rarinervis, Neuropteris vermicularis, all commonly represented in the true Carboniferous. The first of these species, only, is found in the Sub-conglomerate measures.
The genus Odontopteris is mixed in its characters and its distribution. It is derived for some of its species from Neuropteris, and allied by others to Sphenopteris. Its distribution is from the Sub-conglomerate to the Permo-carboniferous and the Permian. No species of Odontopteris are described from the Devonian of Canada.
Dictyopteris is nearly identical in its characters with Neuropteris. Of the two species described, one, from the lower Carboniferous, represents the section of the Nephropterids; the other, related to the Neuropterids proper, especially to Neuropterids Loschii, is, like this species, distributed through all the stages of the coal measures, from the Sub-conglomerate to the Permo-carboniferous.
From the Neuropterids we pass to the Alethopterids by Lescuropteris and Callipteridium. These two genera are allied to the Neuropteris by the venation, and to Alethopteris by the ramification, the mode of division of the fronds and the shape of the leaflets. The fructifications of Callipteridium are scarcely known, for the only fructified fragment referred to the genus, that of Callipteridium inflatum, is too small to allow a deduction on the characters of the fructifications of the group. Species of this genus have been referred by authors to Neuropteris, Alethopteris or Callipteris. The two species of Lescuropteris are limited to the upper Carboniferous; of Callipteridium, three species are in the Sub-conglomerate, the habitat of the others (except one) is limited to the lower Carboniferous A, B,. C.
Alethopteris has in Canada one devonian species; four are exclusively sub-conglomerate in the United States coal measures; of the others four ascend to the upper Carboniferous. The genus is represented also in the Permo-carboniferous and the Permian.
The type is not sufficiently allied to the Neuropterids to indicate a distinct derivation through the genus Callipteridium. It rather seems to be an original one, anteceding and foreboding the great division of the Pecopterids. Its fructifications as far as known by Alethopteris Gibsoni are marginal like those of the living Pteris aquilina to which Brongniart compares the genus.
For Alethopteris, as for some other groups of plants of the Carboniferous, the original species or those nearer to the point of origin are the largest, more fully developed than the descendants. Thus we pass from the large-leafed Alethopteris discrepans of the Devonian, Alethopteris maxima and Alethopteris grandifolia of the Sub-carboniferous to Alethopteris Serlii, Alethopteris lonchitica of Coal A, B, C, then to Alethopteris ambigua reduced in size, ascending to the upper coal and then to Pecopteris. The same decline is marked from the Megalopteris to the Neuropteris, Dyctyopteris, etc.
The genus Pseudopecopteris, composed of species closely allied together, distantly related to Alethopteris and Sphenopteris, is altogether a peculiar group, not less distinct in its characters than in its distribution. All the species, except three, indifferently referred to the genus, inhabit the Sub-conglomerate and the lower Carboniferous.
The genus Pecopteris has in the U.S. Coal measures a single representative below the Conglomerate, Pecopteris angustissima, a rare form here as in Europe. A few species of the genus, some of the division of the Goniopteris, and most of those of the Crestate and Villous groups, have their habitat limited to coal A. But generally the genus Pecopteris is more abundantly distributed and more diversified in the upper Coal measures. The common species, Pecopteris arguta, Pecopteris oreopteridis, Pecopteris platyrachis, Pecopteris dentata, Pecopteris elliptica, Pecopteris Miltoni, pass upwards to the Permo-carboniferous, even to the Permian. The two last species, with Pecopteris arborescens and Pecopteris nodosa are not found lower than the middle coal E.
The Sphenopterids are Sub-conglomerate or lower Carboniferous; very few of them pass above the middle coal E. A peculiar group of this genus allied to Pecopteris appears in the Permo-carboniferous and is limited to that horizon.
The genus is diversified in its types; some of them appear to be original. Sphenopteris Hoeninghausii Brgt., one of the more abundant species of the Sub-conglomerate, already present in the Devonian of Canada, is represented here as in the Culm of Europe by a number of closely allied forms, mostly composing the group of the Hymenophyllites. Eremopteris and Triphyllopteris, separated by Schimper from Sphenopteris, are evidently derived from Archaeopteris, having also the same distribution, all in the Sub-conglomerate or still lower.
The trunks of Fern trees, Stemmatopteris, Caulopteris, Psaronius, Megaphytum, rare in Europe, are in the U.S. Coal-measures, if not abundant, at least often found in the lower and middle Carboniferous. Three species are mentioned in the Devonian of Maine, none from the U.S. Sub-conglomerate.
Silicified remains of Psaronius and of other Fern trees abound at the horizon of the Pomeroy coal of Ohio.
§ 60. The Lycopodiaceae of the coal, known mostly in their fossil state by remains of trunks and branches, compose an original group which, though very distinct, is much diversified in its character.
The oldest plants of this order traced in the Silurian belong to Lepidodendron and to Psilophiton. The distribution of this last genus seems limited to the Lower Devonian. A few fragments of Psilophiton princeps have been found in the Devonian of Maine; none have been seen in the U.S. Coal measures. The characters of the genus are not yet fully defined.
All the Lycopodiaceae have the same essential characters and therefore appear derived from a same stock. From the Devonian, where, in the U.S., seven species have been found already, they rapidly increase in the number of their representatives, becoming most predominant at the horizon of the Conglomerate, where the coal strata under and above this formation are mostly composed of their remains. From the third Coal C upwards they follow a contrary and quite as rapid movement of decadence, so that very few Lycopodiaceae are recorded from the middle Carboniferous. One species only is referable to the upper strata. It is a branch of a peculiar Lycopodites, Lycopodites strictus, found near New Harmony, Indiana, in the shale of a coal bed whose horizon is not positively ascertained.
§ 61. The Sigillariae, known like the Lycopodiaceae, merely by remains of trunks, and characterized by the scars left upon the bark at the points of attachment of the leaves, constitute also a well-defined group, whose relation, however, to plants living at the present epoch is far from being ascertained. They are also evidently derived from a single ancestral stock, already recognized in the Silurian. A few species have been discovered in the Devonian of this Continent; three of them are described by Prof. Dawson, from-this formation in Maine and New York State. We have in the flora six Sub-conglomerate species. In the Lower Carboniferous, the number is greatly increased, but they are there in a far less proportion than Lepidodendron, which Sigillaria gradually replaces, becoming mostly predominant in the middle Carboniferous, and continuing in a limited degree into the Permo-carboniferous and the Permian.
Stigmaria has a far more general distribution than Sigillaria. Its remains abound everywhere as well in the Sub-conglomerate as in the true Carboniferous. They are of less frequent occurrence in the Permian.
§ 62. The Cordaiteae are also an original group distinctly limited in its characters and generally distributed from the Devonian to the Permian, most abundant at some peculiar localities, but without distinct predominance in regard to stratigraphical distribution. Their relation to plants of our time is, like that of the Sigillariae, still uncertain. They belong, evidenly, to the Gymnosperms, and, as remarked in the description of the order, are considered by Renault as related essentially to the Cycadeae.
Accepting this conclusion, I may repeat now with entire confidence an assertion somewhat hypothetically expressed years ago: that until now no trace of the Conifers have been seen in the U.S. Coal-measures. The first and only coal plants which may be referred to Conifers are the Salisburiae (the Ginkgo). Whittleseya seems more distinctly related to Cordaites, but may be an intermediate type; while, evidently, Saportea and Baiera of the Permo-Carboniferous*
§ 63. The reference of the numerous fruits and seeds described in the Flora is not positively ascertained. A number of them are evidently mere capsules or sporanges, containing seeds of Lycopodiaceae. Others are recognized as pertaining to the Cordaites; authors ascribe a number of them to Sigillaria. In their distribution they essentially range like the Lycopodiaceae from the Sub-conglomerate to the middle Coal E, mostly under, within, and immediately above the Conglomerate measures.