« ZurückWeiter »
time the herbage of the wheat has been infested with its parasitic fungus, the Puccinia Gräminis; a coincidence which, it is presumed, ought rather to be interpreted as pointing to certain foregone conditions of the atmosphere or soil, which promoted the growth and multiplication of the respective funguses contemporaneously, each in its own appropriate soil, the leaves or herbage of the kind of plant in and on which it flourishes. That the fungus of the leaves of berberry can grow on the herbage of wheat, or the fungus of the herbage of wheat on the leaves of berberry, is an idea which the conclusions of science wholly repudiate. The first origin of the funguses, and their appointed agency, must be deemed identical, in time and source, with those of the largest of plants. – J. D.
ARt. VIII. A Description of a Fossil Vegetable of the Family Fucoides in the Transition Rocks of North America, and some Considerations in Geology connected with it. By R. C. TAYLoR, Esq. THE accompanying drawing represents an interesting fossil which abounds in certain parts of the transition series in Pennsylvania. This plant was noticed, for the first time, in 1831, under the name of Fucoides alleghaniénsis, by Dr. Harlan, in the Journal of the Academy of Natural Sciences of Philadelphia. Dr. Harlan's description of this fossil Fúcus is so applicable to the specimen before me, that I shall take the liberty of condensing his account. “It presents one of the richest specimens of vegetable organic remains that have hitherto come under my notice. Not only is the surface of the stone crowded with the forms of this plant, but they lie upon each other three or four layers deep, as is demonstrated by a horizontal fracture. They project in bold relief from the surface, with their distal extremities disposed in every direction; they appear to have been of different ages, and vary in size, accordingly, from 2 in. to 5 in. in length, the largest being eight tenths of an inch in thickness. In breadth they vary from one to five tenths of an inch ; they are generally gently arched from the base towards the apex, and more or less recurved at top; in every instance the apex is curved downwards, and sinks into the stone. The superior surface of both the stalk and branches is cylindrical, transversely wrinkled by irregular channels, and marked by a longitudinal and depressed line. The digitations or branches are all compressed laterally as well as the stalk, and are fasciculated or closely applied side by side at the commencement, and gradually diverge towards their distal extremities. “In every case the stalks divide into two or more branches; the latter are more or less wrinkled, apparently according to age, the rugae being more or less obsolete in the largest, profoundly developed in the smaller or younger specimens. The plants are fractured in many places and in various directions; but the fractured portions do not display any evidence of organisation; nor is there any appearance of leaves, nervures, or fructification.” I believe that a fossil of this description has not been noticed in any part of the transition series in Great Britain : yet, as some traces may be discovered through the aid afforded by an accurate illustration, I am induced to transmit some further notice of this fossil plant and of its geological position. Mr. De la Beche enumerates two or three species of Fucöides in the grauwacke group of Europe. How near they may approach to the fossil which is so strikingly characteristic of a part of the same group in North America, I have no present means of ascertaining. The two species found in the transition limestone of Canada are dissimilar to the Fucóides alleghaniénsis. The aggregate thickness of the grauwacke group is enormous in Pennsylvania; its breadth being about 120 miles, and its stratification being inclined at a very high angle, and often approaching to verticality, it is not improbable that the entire mass averages forty-five degrees. I have examined a large portion of this in detail, and have constructed a transverse section of about seventy miles, from which it appears that in about half this breadth the inclination of the rocks is towards the Alleghany chain, and in the other portion it is reversed. On the details of the subordinate portions of this group it is not my intention to enlarge. It is sufficient to observe, generally, that they consist of arenaceous, slaty, and limestone rocks, subdivided into innumerable varieties of siliceous and argillaceous beds, conglomerates, shales, clays, marbles, flinty slate and flinty limestone; and include numerous coal seams, both of anthracite and of the quality which may be termed bituminous anthracite, and large deposits of iron, both argillaceous and haematitic. The surface of this region is broken into an infinite number of sandstone ridges and limestone valleys, all running parallel with the mountain chain of the Alleghany. These ridges are generally 700 or 800 feet above the valleys, and are incapable of cultivation. They are covered,
to the thickness of from 10 to 100 feet, with huge blocks of sandstone. Upon their steep sides few traces of vegetable soil exist; yet the oak, the chestnut, the pines, and several other trees, have obtained a firm footing, and have extended over the loftiest crests. Embarrassed with this accumulation of debris, the geologist seeks, almost in vain, for some exposed face, some unencumbered surface, to determine the arrangement and structure of these vast and singularly prolonged masses. He finds as much difficulty in viewing the details of their geological features, as in obtaining, from amidst the ancient forests which overshadow them, an uninterrupted view of the wide-spread landscape beneath his feet. I have observed Fucóides alleghaniénsis, at points 150 miles remote from each other, in the sandstone ridges that occur parallel with the eastern side of the Alleghany Mountains; but nothing resembling them can be detected in the intermediate limestone valleys. The subject of my sketch (sg. 6.) was
derived from the vicinity of this place [Lewistown], on the banks of the Juniata River, and in the same district from which Dr. Harlan's specimen was procured. Detached fragments, rolled from the mountains, and fallen slabs, exhibiting fine specimens of this fossil, are not unfrequently met with amidst the talus of the ridges; but it is only very recently that the beds in which it occurs in situ came under my observation. Under the conviction that these vegetable strata have hitherto escaped geological notice, I proceed to detail some circumstances relating to their position. After passing Lewistown, the Juniata flows easterly, for
about six miles, through “ the Narrows;" that is, in a deep narrow trough between the two sandstone ridges of Shade Mountain and Black Log Mountain ; having, for the most part, barely space for its channel. The great western turnpike road and the Pennsylvania Canal also pass through this ravine; being, for some distance, excavated out of the base of the northern ridge, called Shade Mountain. In consequence of these public works, many of the inferior strata are here exposed ; and although, in the aggregate, they do not comprise a thirtieth part of the entire elevation, they are highly interesting, in displaying beds of fossil Fùci in unexpected abundance.
These beds, where I first saw them extensively intersected, consist of fine-grained compact white sandstone; interstratified with greenish argillaceous seams, and some laminæ of black shale, both containing mica. Upon the upper surfaces of the argillaceous slabs are disposed innumerable groups of Fucöides. Above these layers, other courses, covered with the same fossil plants, could be traced obscurely; while masses of hard sandstone, whose figured surfaces bore rude resemblance to the Gothic tracery of ancient sculpture, had evidently fallen from much more elevated sites.
Pursuing the examination farther eastward, the beds of Fucoides were again laid bare, by the canal excavations, to the height of 50 ft. above the Juniata. Here I counted seven courses of them, comprised within the thickness of 4 ft. Among the lower beds are some of white cherty sub-crystalline sandstone, and others composed of micaceous schistose sandstone, whose upper surfaces were traversed by another species of Fucöides, distinguished by their long curving stalks ; whilst upon other argillaceous slabs a third description of fossil Fuci crossed each other in straight lines, resembling network. It may be remarked, that no casts of shells, nor, indeed, any other organic body, occur with these deposits.
At another point, three miles eastward of that where I commenced tracing the Fucus beds, numerous seams of fine white sandstone, separated, as before, by thin courses of micaceous shale and clay, are exposed. Some idea of the rapid succession of vegetable deposits will be conveyed, when it is mentioned that eight or ten were numbered within the space
of 6 ft., some of them not exceeding 1 in. thick. The surface of Shade Mountain is too much obscured, by its thick covering of coarse debris, to enable an examination of its structure to be satisfactorily pursued; but there is reason to conceive that these fossils occur at various elevations, besides those of which I have spoken. I have observed them at 100 ft., 150 ft.,
and at 500 ft. above the Juniata; and specimens have even been obtained from the summit.
The strata I have enumerated dip towards the north-west generally; but local derangements have occasioned some partial curvatures and arching of the inferior strata, so as to occasion a variation from 30° N.W. to 60° S. The valley of the Juniata is remarkable for the singular contortions, on a large scale, of the strata upon its banks.
Lower down the Narrows succeeds a variety of argillaceous beds, which furnish the flagstones for the side pavements of the town of Lewistown. The surfaces of these pavements are covered with irregular protuberances, evidently of vegetable origin, and, probably, another species of fossil A'lgæ. Beyond this point another series of strata occurs. These consist of red sandstones, interlaced with numerous veins of white quartz, and conglomerates of granulated quartz, intermixed with fragments of red micaceous slate. Even these rocks occasionally exhibit coarse impressions and casts of Fucoides. To these succeed thick deposits of black shale, having no trace of organic remains.
The strata which I have thus briefly enumerated, although they form but an insignificant fraction of this immense series, present matter for the consideration of the speculative naturalist. It has been seen that here occur many alternating beds of Fucoides, and, probably, several species of these fossil plants. Hence may be inferred the existence, at various epochs, of so many separate surfaces, on which vegetation flourished at the bottom of an ancient ocean.
We thus ascertain that, in those remote times, there were frequent successions of these remarkable submarine plants, and many renewals of the argillaceous surfaces upon which they took root. But it does not appear that the consequence of these frequent changes was the obliteration or destruction of the organic forms of the vegetation so overwhelmed. The entire series, from the lowest bed even to the highest, appear to retain their original distinctness of outline.
In the phenomena of deposition, and of recurring vegetation we may, perhaps, trace some circumstances analogous to the formation of coal beds.
The figure which illustrates this article represents a group of Fucöides, on a scale somewhat less than half their actual proportions (the drawing was about an inch too wide for our page]. An assemblage of these groups, ornamenting the surfaces of large slabs, in clear relief, forms one of the most remarkable fossil productions of this continent. Imagine beds of these Fucoides miles in extent, deposited, or rather accumu