a portion of clay considerably above the shells. Other plants are a new species of Podozamites (P. proximans Conrad, described below), nearly related to P. lanceolatus Emmons; a Cyclopteris which is probably identical with Emmons's species, figured in the geology of North Carolina, vol. i, p. 4, fig. 10. This is extremely abundant in the lower part of the bluff, in the light colored clay which rests on plicated sand. The latter no doubt is part of the same formation, and overlies the Red Sandstone of New Brunswick, and although the point of junction is unknown, the Raritan clay and the red sandstone may be traced within two miles of each other. Impressions of the leaves of this Cyclopteris are extremely numerous, whilst the stems are also abundant, generally in a vertical position, or so inclined and disturbed as to suggest an agitation from wind or eddies placing them in a position in which the sediment preserved them. Description of a new Cycadaceous plant from the Raritan Clay. PODOZAMITES. Podozamites proximans Conrad. Lanceolate, gradually tapering at base. Locality, near Washington, on South river, N. J. These plants go far to prove the Raritan clay to be of Triassic age, but I have further evidence in the shells to convince me that it is the equivalent of the Muschelkalk of Upper Silesia. Dunker in "Paleontographica," describes and figures some bivalves of the Muschelkalk of Silesia, which if not identical with the shells of the Raritan clay, must be nearly allied species, if external form is of any value for comparison. Dunker's shells are very perfect, and the hinge character well represented. They constitute a group in the genus Astarte, wholly unlike any that existed before or after the Triassic period, and one species at least I cannot distinguish from one in the Raritan clay. This genus Astarte of Sowerby originated in the Triassic period, and culminated in the Jurassic. In the first the species are few, plain and small. In the latter they are large, with great variety of form, and the generic character greatly developed. I am not sure whether A. concinna of the lower green-sand is a true Astarte, but if it should be, I believe that this formation holds the last of the genus. I find none in the chalk or its representatives. Crassina Lam., with which Astarte is usually confounded, originated in the Miocene period, and appears to have culminated in the North AM. JOUR. SCI.-SECOND SERIES, VOL. XLVII, No. 141.-MAY, 1869. American seas of this age, for we know eighteen species, while there is but one recent on the coasts of the Middle States, and four on those of the Eastern. A singular cast in the Muschelkalk of Silesia is figured in "Paleontographica," vol. 1, tab. xxxii, fig. 33. Dunker remarks that it has some resemblance to a valve of a bivalve shell, but I have the best authority for pronouncing it a form of Entomostraca, though differing from any recent genus. I found a cast of the same genus in the Raritan clay, of a shorter outline than Dunker's, and with only three tubercles. The latter has five or six equal tubercles, situated like the Raritan species on the lower submargin. I propose to name this Triassic genus Paleocypris; the American form P. trinodiferus and the European P. triassina. The former is distinctly visible with a lens. In a small mass of ash colored clay taken from the lowest stratum, a few fern roots are well represented in pyrites, of an upright habit, and not creeping like the rhizomes of existing ferns. The secondary roots are numerous, some of the laterals as fine as hairs, and from the base of the main root large branches run downward. This must have been a bed of ferns growing in a sandy, slightly micaceous clay, and yet in this indifferent soil grew long, stout, flexible stalks strongly striated longitudinally. The foliage is yet unknown, for the stalks are cut off as it were by a black clay above, in which the traces of vegetation are obliterated, although the dark color of the clay is derived from carbonized leaves. Above this four feet of a black stratum, there is a thick mass of ash colored clay, in the lower part of which are innumerable impressions of a Cyclopteris, the leaves of which are of a peltate form, and the stalk differs in its character from those of the lower bed. It is not longitudinally striated, but irregularly plicated. There are probably two or more species, but the imperfect specimens do not indicate the difference. F. A. Roemer has figured a fossil which he named Cyclopteris peltata, but the nervation is wholly unlike that of the Raritan species if his figure is correct, the nerves in which are not branched. One of our species resembles the leaf figured by Emmons, which is too imperfect in outline for comparison, but the nerve character is similar. There are two European species described with peltate leaves, and both by the same name, C. peltata Göppert, of the Lias, having priority over Roemer's name of peltata. The former also differs from the New Jersey species in a simpler or less branched form of the nerves. One of the fragments of a Cyclopteris in the Raritan clay has a deeply sinuous margin, and when entire, was over two inches in length. In this bed, just over the black clay beneath, a patient search revealed the presence of fresh water shells, two or three species of Pisidium, and one apparently of Cyrena, which would indicate this line of the high lands on the south side of the Raritan to have been a wide estuary, although no other trace of the rivers on land of this period is known. About a quarter of a mile east of this bluff in the suburbs of Washington, I observed similar clays at about the same level, and in the black stratum, leaves as abundant as it would be possible to press them. Lignite is plentiful, and large fragments of the trunks of trees. The clays around Baltimore are supposed, with reason, to be synchronous with the Raritan clays, and therefore it is highly probable that the fossil forest at the mouth of the Patapsco, described by Durand, may be of the same geological age. EOCENE AND MIOCENE OF SHARK RIVER, N. J. The village of Trap on Shark river shows a good section of Eocene greensand, overlaid by about six feet of Miocene marl. This Eocene is known by the name of Squankum marl, and contains few organic remains. Prof. Cope has described two species of Paleophis; and a Calorhynchus also occurs in it. I have no doubt that Leidy's Anchippodus riparius was obtained from it, and that it was an Eocene pachyderm. Equally certain am I that the peccary tooth described by Leidy, found at Shark river, was a Miocene species. It was picked up by Dr. Kneiskern at my feet while walking with him over a bed of Miocene marl, replete with shark's teeth, and at some distance from the bluff from which it came. The color, mineralization, and degree of corrosion, all agree with the shark's teeth, and with a cast of Volutilithes found on the same spot, and which latter fossil is composed of a light ochreous impure limestone. Prof. Leidy would refer this specimen to his Dicotyles nasutus if it had been found in the same bed. This species was obtained in digging a well in Indiana, at a depth of 30 or 40 feet, and referred to the Post Pliocene period, without any evidence that the deposit belongs to that period. On the contrary, there is reason to believe that the animal lived at the same time with the fossil Unionidæ near Marietta, Ohio, both the peccary and the shells being found at a depth of about 40 feet, and that the same quadruped lived at that time in New Jersey. This will give some idea of the extent of land in the Miocene era, and the only reason why we have so few traces of the Miocene continent west of the mountains is because it is buried below the surface, and only made known to us in digging wells. On the contrary the Post Pliocene beds are often seen in the river banks and contain shells of existing species, while a more trenchant line of demarkation is nowhere seen than between these periods, as we might expect to be the case where the long interval of the Pliocenes has passed between them. The Miocene line at Shark river is distinguished by a thin layer of calcareous earth replete with the teeth of several species of shark, of a pale ochreous color, whilst those of the Eocene are black; over the layer above mentioned is about six feet of dark Miocene marl, nearly or quite destitute of organic remains. The upper part of the Eocene is a hard gray rock, about four feet thick, abounding in large green grains, and holding numerous fossil remains, among which Aturia is most characteristic of the geological age of the formation; below this of unknown depth is the loose green-sand with a few Eocene species of reptiles, mammals, fishes and plants. ART. XXXV.-On certain Phenomena of Transmitted and Diffused Light; by M. CAREY LEA, Philadelphia. WHEN a beam of sunlight is thrown upon a white screen at the distance of fifteen or twenty feet and a plate of finely ground glass is interposed in its path, the white light by passing through the colorless glass acquires a deep orange yellow coloration. A greenish or bluish tinge in the glass does not interfere with the experiment, but it is necessary that the grinding of the glass be exceedingly fine, the surface must be scarcely removed, and with the finest emery. This experiment, which admits of some very interesting variations that will be mentioned farther on, is, I believe, new. Those upon record which approach most nearly to it, relate to certain properties of milk and of magnesia respectively, which when diffused through water produce a reddish diffuse transmitted light, and a bluish diffuse reflected light. My own experiment just mentioned, differed from these in two points; first, that the red transmitted light was direct, and not diffuse; and secondly, that the blue diffuse light was wholly wanting. Nevertheless, a study of the phenomena led me to the conclusion that these several experiments as well as many other new ones, depended upon the same cause, and that consequently the explanation given for the few cases that have been up to this time observed and described, is insufficient. Becquerel in speaking of the two cases just mentioned, viz: magnesia and milk, observes in his very valuable work on Light: "La diffusion qui est tres-forte pour les rayons très-réfrangibles fait paraitre ces corps blancs et même bleuatres par reflexion, et jaunatres par transmission. En effet la lumière transmise comprend celle qui échappe à la diffusion par reflexion ainsi qu'à l'absorption; plus cette diffusion est grande, plus la partie est faible à égalité d'absorption, et vice versa; en outre la couleur des rayons diffusès est complémentaire de celle des rayons transmis.”* This indeed can scarcely be called an explanation, it is rather a re-statement of the facts in a more general form and simply affirms that the red rays have a greater tendency to be transmitted and the blue to be diffused. Nor does this seem to have been deduced from any observed properties of light, but appears to have been adopted from an analogy real or supposed, with properties of heat. It will be necessary therefore to glance for a moment at these properties of heat. In 1840, Melloni showed the necessity of admitting the existence of a diffusive power in heat, from overlooking which, a large portion of the experiments recorded up to that time, were rendered inconclusive, especially those of Leslie, some of which till then, had been looked upon as fundamental in establishing the laws of heat. Up to that time, when heat fell upon any surface, it was held to undergo specular reflection, transmission and absorption. Melloni added to these, diffusion. To enter at large into his experiments would take up too much space here. The essential point is, that, taking rays of heat, chiefly of high refrangibility, issuing from a lamp, he sifted out from these the rays of less refrangibility by causing them to pass through a lens, which at the same time, rendered them nearly parallel. These rays were then allowed to fall upon a disc of pasteboard covered with white lead. A thermoscope placed so as not to receive rays specularly reflected, was nevertheless powerfully deflected. To ascertain whether or not this deflection was produced by radiated heat, he interposed a screen of glass between the disc and the thermoscope; scarcely any diminution of the deflection followed. Had the rays been absorbed and radiated, they would have been of low refrangibility and would have been to a large extent, stopped by the glass screen. As they were not so stopped they were evidently rays of high refrangibility issuing from the lamp. The thermoscope being carried around the disc at the same distance and angle indicated an unvarying deviation. This showed that the effect observed could not arise from specular reflection. It therefore followed that the deviation of the thermoscope was due to a function of heat different from any previously recognized, distinguished from specular reflection by the fact * Becquerel, La Lumiere, ii, 10. |