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 Algæ. 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 ascer tain 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 Fucoides, 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 lated, layer over layer and growth over growth, until the mass Lewistown, Mifflin County, Pennsylvania, ART. IX. Remarks and Illustrations on the Decay of the Stems of succulent Plants. By FREDERICK C. LUKIS, Esq. THE fossil vegetables which are found in the secondary formation, designated as coeval with the consolidation of the sandstone and coal measures, present to the eye of the observer patterns of great beauty and regularity, and display figures which have been often compared with the eccentric ornaments of ancient architecture. Without entering into the general geological hypothesis, much may be done, in the study of these interesting remains, by close investigation and analogy; and, indeed, the nature of fossil vegetables must receive its principal elucidation from the careful examination of existing species analogous to them, when they can be found. The physiological botanist is well aware that plants in decay are disposed to shrivel up, each in a manner peculiar to its own class, and that this operation is governed by their internal as well as external organisation, and by the circumstances under which they may be placed. As the greater number of our fossil plants have been referred to the ferns, cactuses, and other succulent analogues, it is among these we are to look for characters of resemblance; and although many of these remains possess dimensions which baffle our conceptions, when brought in comparison with our pygmy tribes of the present economy, still the latter, insignificant as they appear, may afford us physiological types sufficiently clear to bring us near the truth. A series of observations made on the drying and decomposition of succulent plants has occupied my attention for many years, and I propose to notify some of the changes remarked in the stems and branches of the Sempervivum arboreum L., or tree houseleek, as it is called, in the course of their decay. They will suffice to show the variety of patterns which may be produced, under favourable circumstances, by a single individual of the succulent class. The result of decay in stems of this plant has been the production of exterior markings, presenting a strong analogy to those of fossil plants; and I may venture to say that, if casts had been taken from them, they would have been mistaken for real specimens of these interesting remains. The plants, when chosen for examination, were old, and of extremely luxuriant growth. The stems had acquired the size of a man's arm, and were about five feet in height. They were withdrawn from the hot-house during a sharp frost, by which they were soon killed. The leaves dropped off, leaving the rudiment more prominent and perfect than when their removal happened by natural decay. After the death of the plants, they were kept in the mould they occupied, and placed in a shaded situation, where decomposition was allowed to proceed slowly for the space of two years. During dry seasons they were occasionally watered, and the upper part of the stems was scooped out so as to admit moisture in the interior soft parts when required: thus a partial fermentation was continued until the medullary substance became dissolved. The first change observable in the appearance of the epidermis was a disposition to form regular ridges or risings in the interstices between the marks left by the leaves and subspinous nerve near them, preserving a reticulated pattern. The hardness of the ligneous centre resisted decay for a long time, and allowed the cortical covering to form its pattern with considerable exactness; and at last, by its own shrinking, and the want of farther resistance from the nerve of spine and leaf, the covering contracted in a longitudinal direction, leaving the end of the wood projecting beyond the upper part of the plant. The following drawings of the plants, taken at different stages of decay, will be better understood than a lengthened description. Fig. 7. represents the common appearance of the stem, deprived of its leaves, before decay; the tubercle and rudiment of the leaf, in quincuncial order, scarcely rising above the epidermis. Fig. 8. This figure shows the first angular depression round the tubercle and leaf, caused by the shrinking of the interior parts of the plant: the dried state of the cortex opposing the contraction of its circumference. Fig. 9. is part of the same stem, contracting more equally downwards, it having been more under the influence of moisture than the lower end. It had now commenced a wavy and rhomboidal cancellated figure, the elevated ridges preserving an almost united wavy line from top to bottom. Fig. 10. The same as the last figure, having now attained VOL. VII.- No. 37. D a more decided pattern, by the completing of the above-stated rhomboidal depressions, which had been assisted by a longitudinal cut of a knife, and the careful removal of the woody Fig. 11. Other parts of the plant produced this pattern. It appeared that the spinous processes in the interior had resisted the vertical contraction of the cortex. Here the spaces retained an oblong form, having the elevated ridges prominent, though not united throughout their diagonal direction, but breaking into distinct approximate compartments, much in the same manner as those in the Phytolithus cancellatus. (fig. 21.) Fig. 12. The most general appearance of the plants, where contraction was carried on more equally from both ends of the branch. The elevated ridges surrounding the compartments had now become dry and hard, and might be said to have arrived at the state of hay. Fig. 13. is a vertical section of a branch, to show the ligneous centre, or woody stem, in a fresh state. Fig. 14. The same after decay had commenced. The woody centre, in contracting, had produced lengthened lozengeshaped elevations, retaining the spinous processes rather prominent. Fig. 15. A longitudinal section of a branch, to show the disposition of the medulla, or pith, in the ligneous centre, where it forms transverse cells: the cortical cells or layers, running in a vertical manner, are traversed by the spinous nerve which produced the elevations in the epidermis. In Fig. 16. represents the base of the stems of old plants. The epidermis becomes hard and leather-like, and is generally ruptured by the enlargement of the subspinous elevations. the case under consideration, it formed lozenge-shaped openings round each tubercle, and retained a slight remain of the impression left by the original leaf across the tubercle. Fig. 17. In this last figure decomposition had affected the interior so as to enable the cortical covering to sink between the stiff prominent spines, which resisted decay with greater obstinacy; thus forming rhombic compartments in a reversed order to what had taken place in the younger branches, as seen in fig. 11. A greater variety of figures might have been produced, but as many were the same in character, under a few modifications, and in progress of decay, I have chosen the most decided patterns only. Some interior changes in the epidermis, cutis, and ligneous centre presented very regular markings during the progress of decomposition and desic cation. Fig. 18., taken from the inside surface of the epidermis of the largest stem, will suffice to show the various changes exhibited by a single plant: in this case the cortical parts, under the epidermis, had separated in macerating, and left it at liberty to produce this pattern, although the exterior surface was not much altered from the rest of the plant. In this figure the hollows were numerous and deeply marked. Over each a transverse, sharp, wavy, elevated line passed in regular succession; undoubtedly formed after its separation from the rest of the plant. These lines were not marked on |