ART. XXXIII.-On some Questions concerning the Coal Formations of North America; by LEO LESQUEREUX.

(Continued from page 74.)

Stratigraphical distribution of the Coal-flora.

DETAILS concerning the stratigraphical distribution of the coalflora of North America, to be intelligible, ought to be prefaced by a few remarks on the order of superposition of the strata of the coal-measures.

A general section, showing the order of stratification in the whole extent of our coal-fields, would appear perhaps merely hypothetical. Such is, nevertheless, the uniformity of the distribution of the strata of our coal-basins, that a section made in Western Illinois or Western Kentucky or in any part of the coalfields of these States, will prove comparatively similar, (that is with some difference in the thickness of the strata,) to any section made in the coal-fields of Pennsylvania or of Ohio. This analogy of stratification has been fully established by a series of comparative sections, reported for the 4th vol. of the State Geological Survey of Kentucky. Such a comparison of sections had been attempted before, for the State of Pennsylvania, by my friend J. P. Lesley, in his excellent Manual of Coal. But it was not based on palæontological evidence and thus the contemporaneousness of the juxtaposed strata was necessarily problematical. On the contrary, by admitting the similarity of the flora of the coal-strata as a coeval mark and as a basis for juxtaposition of the strata, the result of the comparison of sections gives evidence remarkable in a double point of view. First it shows, by juxtaposition of the coal strata of which the shales contain the same species of fossil plants, the uniformity of stratification in the whole area of the coal-fields of the United States; and secondly it proves that the distribution of the coal plants has followed the same developement, the same successive modification in the whole extent of the same coal-field.

Though plants of carboniferous genera are found below the bed of the Archimedes or mountain limestone, as, apparupper ently, no coal has been formed at this low station, I take as the base of the true coal measures this Archimedes limestone, replaced in Eastern Pennsylvania and Northern Virginia by the red shales of the old red sandstone. From the top of the mountain limestone, to the top of the millstone-grit series, including some beds of coal at its base, the average thickness is from three to four hundred feet. The upper part of the millstone-grit series, sometimes its whole thickness, is a compound of coarse sandstone, shales and especially conglomerate, the last predominat

ing. The conglomerate formation thickens wonderfully at some places, generally increasing westward. Its greatest thickness, in the sharp Mountain near Pottsville, Penn., is 1100 feet.*

To elucidate the details of this general section, we can admit the numbered division of the coal strata, as it has been most satisfactorily established by Dr. D. Dale Owen for the State Geological Survey of Kentucky, vol. iii, p. 18. From the top of the millstone-grit to the base of another great sandstone formation, the Mahoning sandstone, there are generally five workable beds of coal. The lowest is No. 1A; then No. 1B to No. 4 inclusively. No. 1B coal is the Big, or Mammoth coal of the East. Like the conglomerate, it increases in thickness progressively westward. The fourth bed of coal is the Pomeroy coal of Ohio. The Mahoning standstone overlying No. 4 bed of coal, like the millstone-grit is generally conglomerate at its upper part. Its thickness averages from one hundred to one hundred and fifty feet. It might, as well as the true conglomerate, be considered as the basis of a new coal epoch; even more so, perhaps, since the vegetation at its base and at its top shows a greater difference than in the coal strata above and below the millstone-grit. From the Mahoning sandstone upward, the marine influence predominates more and more and the shales of the coal strata more generally contain remains of fishes and of marine shells than of terrestrial plants. This Mahoning sandstone is separated by about 500 feet of strata from another great sandstone formation still resembling in its composition and thickness the Millstone-grit or conglomerate. It is the Anvil-rock sandstone of the State Geological Survey of Kentucky. The 500 feet of measures between it and the Mahoning, are sometimes barren of coal. But westward they contain from Coal No. 6 to No. 12, five workable beds of coal and two, scarcely if ever, of a workable thickness.† The highest coal strata of this section, Nos. 11 and 12 united together, form the great Pittsburg coal bed of Pennsylvania.

Above the Anvil-rock sandstone, there are still 500 to 700 feet of coal measures, in which some thin beds of coal are formed. But this examination of the flora of the coal measures can not be extended higher than the Anvil-rock. The upper division has been locally washed away by erosion and where it is still present, its coal beds are too thin for working and thus their unexposed shales can not be satisfactorily examined. Near Shawneetown, Illinois, the first coal above the Anvil-rock

* H. D. Rogers's final report of the State Geol. Survey of Pennsylvania, vol. i,

p. 109.

+ In those coal regions of the United States where coal is abundant, a bed of bituminous coal is not remunerative, when under a thickness of three and a half feet. In the Anthracite basin, the working becomes unprofitable for a bed of less than two and a half feet.

sandstone has a roof of laminated sandstone, blackened by broken and undeterminable leaves and small stems of ferns. The second bed at the same place contains only fossil shells and remains of fishes.

The first trace of a terrestrial vegetation in the Paleozoic strata of North America appears in the Marcellus shales or middle Devonian, in a species of Lepidodendron named L. primævis by Prof. H. D. Rogers. It has not been described, but only obscurely figured by a wood-cut; and as I have not seen the specimen and could detect at the place where it has been found, near Huntingdon, only detached leaves of this species, its relation or its specific value is unknown to me. In the Devonian black shales of Ohio, and perhaps of Illinois,† large silicified trunks of trees have also been found, always very rare and at far distant localities.

Ascending higher, we find species of Lepidodendron, of Sigillaria, and especially of Calamites and stems (Bornia Sternb. and Stemmatopteris Göpp.) in the transition series of the Old Red sandstone of Pennsylvania, and especially in the Mountain limestone by which it is represented in the Western States. Leaves are very rare in this formation and of a different type from those of the coal measures. Heretofore, all those which have been found belong to the genus Noeggerathia (Sternb.), of which I have never seen a single specimen in the true coal measures. Below the 3d or upper Archimedes limestone, there is in Illinois and in Arkansas a bed of schistose sandstone which, with peculiar species, already contains some others of the true coal measures. In the Cabinet of the State Geological Survey of Illinois, I have seen from this subcarboniferous sandstone, specimens of Stigmaria anabathra (Corda), and Göppert's varieties: minor, and undulata, reticulata, stellata; of Lepidodendron Veltheimianum Sternb., a species peculiar to the transition series, both in Europe and America; of Lepidodendron Worthianum Lsqx., a beautiful species related to L. Volkmannianum Sternb.; one Lepidodendron sp. nov.; one Caulopteris, one Megaphytum, all three new and undescribed species; Calamites Suckowii Brgt.; one Bornia Sternb.; * Final report of the State Geol. Survey of Penn., vol. ii, p. 828.

Mr. A. H. Worthen, State Geologist of Illinois has in his cabinet this Devonian silicified wood without label of locality. It is also in the cabinet of Dr. D. Dale Owen at New Harmony, also without label, All my specimens have been cut from a large tree protruding from Devonian strata near Delaware, Ohio, and discovered by Dr. Mann, who kindly communicated them to me. It is by all appearance the wood of a Lepidodendron, and it will be figured and described with the silicified Psaronius of the coal measures.

Dr. Newberry mentions in his catalogue two species of Noeggerathia found in the coal above the conglomerate. One is Noeggerathia Beinertiana Göpp., a species evidently referable to Cordaites Ung, and probably only a small form of Cordaites borassifolia Ung. The other is Noeggerathia microphylla Newb., undescribed and consequently unknown to me.

AM. JOUR. SCI.—SECOND SERIES, VOL. XXX, No. 90.--NOV., 1860.

Cordaites borassifolia Ung., Knorria imbricata Sternb., and some undeterminable stems. From these plants, six have been found also above the conglomerate series, ascending to coal No. 1B, or even higher. They are Stigmaria anabathra, var. undulata Göpp., and var. minor Göpp., Lepidodendron Worthianum Lsqx., Knorria imbricata Sternb., Calamites Suckowii Brgt. and Cordaites borassifolia Ung. These two last species are present in the whole thickness of the coal measures, as high at least as the 12th coal.

As I have said before, no coal has been seen as yet formed below the 3d Archimedes limestone. But just overlying it, a bed of coal is generally present over the whole extent of the Western coal-fields. In Arkansas, this is the only workable bed of coal, its thickness varying from 18 inches to 4 feet. In the western part of the Eastern coal-basin of Kentucky, and also in Virginia, two, even three beds of good coal have been formed below the millstone grit. All the species of fossil plants of the shales of these coal strata have been found also in Arkansas. At Pottsville and Mauch Chunk, near the eastern margins of the coalfields, the coal is formed between strata of conglomerate, and even at the base of this formation.

The shales of the subconglomerate coal contain not only remains of trees of large size, like the subcarboniferous sandstone, but thus early and simultaneously many of the species of ferns which become more and more abundant above the conglomerate series. Thus Pecopteris velutina Lsqx., Neuropteris flexuosa Brgt., N. hirsuta Lsqx., Sphenophyllum Schlotheimii Sternb., Pecopteris nervosa Brgt., Annularia sphenophylloides Ung., Odontopteris crenulata Brgt., Cordaites borassifolia Ung., Hymenophyllites furcatus Brgt.: and Sphenopteris latifolia Brgt., all found there in connection with it, ascend to coal No. 1B or higher. Among the trees seen in this coal, and ranging still higher in the measures, there are six species of Lepidodendron, two of Sigillaria, two Calamites, Stigmaria and its varieties, and a few species of Carpolithes and of Cardiocarpon. Though this subconglomerate coal has not been yet explored over a large area, it shows already more than twenty species, representing all the essential genera of our coal-plants, which have a wider range of distribution, and appear still in the coal strata above the conglomerate. It is therefore evident that a separation of the subconglomerate coal, as a peculiar formation and under a peculiar name, is contrary to paleontological evidence. Like every other coal bed the subconglomerate coal has species peculiar to it. Two species of Lepidodendron, two of Sigillaria, one of Sphenophyllum, two species of Trigonocarpum, one very large Cardiocarpum, one Stigmaria, one Alethopteris, and three or four Sphenopterideæ. In the shales of this lowest bed of coal, near Frog

* All the new species of this coal, or at least most of them, belong to the State Geological survey of Arkansas, and are reserved for publication in the second volume of that Report.

Bayou, Arkansas, I have found for the first time in America one of those beautiful wings of insects, referred by M. Germar to the genus Blattina. Though related to Blattina didyma Germ., our American species is new.

The first bed of coal above the conglomerate, our No. 1A, is generally thin (two feet to four feet thick at the most), and overlaid by a stratum of coarse sandstone or of black very bituminous shales. In the shales, I have never found any other remains of plants, than leaves and cones of Lepidodendron, six species of Lepidostrobus and Lepidophyllum. The shales are too bituminous for good preservation of specimens. With the remains of plants, the shales generally contain a few specimens of Lingula umbonata Cox, a shell extremely abundant in the shales of No. 1B, and rarely represented by a very few individuals in the coal No. 2. Sometimes coal No. 1A and No. 1B become united together, being separated only by a thin parting of shales, but more generally there is between them a stratum of coarse sandstone, marked with numerous prints or casts of great vegetables of the coal, especially of Lepidodendron obovatum Sternb., L. rimosum Sternb., L. rugosum Sternb., L. aculeatum Sternb., Sigillaria alternans Ll. and Hutt., S. reniformis Brgt., S. Brardii Brgt., S. laevigata Brgt., Sirigodendron pachyderma Brgt., and some fruits, Carpolithes and Trigonocarpon. Other species, one Caulopteris, one Megaphytum, some Calamites, all rendered undeterminable by the coarse compound of the sandstone, have been seen in this stratum.

Coal 1B. Its horizon appears to mark the epoch of the highest development of the vegetation of the coal formation. Not only is this coal bed the most reliable of all, and consequently the most extensively worked, not only does it attain locally an enormous thickness, justly meriting the name which it bears in some parts of Pennsylvania, viz., the Big Coal, the Mammoth vein, &c.; but the shales which cover it and sometimes divide it into two, three, or more members, afford to the explorer the greatest amount of species, distributed among nearly all the genera of plants which belong to the coal formation.

The vegetation of coal No. 1B may be characterized: First, by the great number of fruits, found in the strata connected with it, either in the shale above or in the sandstone below. Indeed, nearly all the species of Trigoncarpum, Cardiocarpum, Rhabdocarpos and Carpolithes belong to it. Its second characteristic, is the great abundance of species of Lepidodendron. Eighteen species of this genus have been found in this bed of coal, and no new species have been, as yet, seen above it. A third character is the constant presence in the shales of our No. 1B of Alethopteris Lonchitidis Brgt. which apparently belongs exclusively to it. Generally speaking, the coal has the great forms of the section of the Pecopterideæ, viz. Alethopteris and Callipteris, and is mostly