and in sand a quantity of this material is thrown out behind, which in a cast would have left two hollows, not present in the fossils; but should a Limulus burrow in fine mud, which would become diffused or washed away as thrown out, then the appearance would be not unlike that of these fossils. The front of the carapace would give the rounded, anterior end; the two rows of walking and swimming feet would form the depressions with transverse striæ; and the only addition would be the mark of the caudal spine of Limulus, of which there is no trace in the fossils. The animal required would therefore be a crustacean, having feet and habits of life generally resembling those of Limulus, but without a caudal spine. The only known animals of the period that could have fulfilled these conditions are the Trilobites; and since the interesting discovery, by Mr. Billings, of the feet, or bases of the feet, of Asaphus, the objection to this view which might have been taken from our ignorance of the feet of these animals, no longer exists. The feet of Asaphus, in short, appear to constitute just such a double series of laminæ as would necessarily produce markings like those referred to.

From the great depth of these burrows, and the indications of shallow water in the vicinity of a shore presented by the shrinkage-cracks, I would further consider it probable that these holes were places of incubation; and that the Trilobites carried their spawn attached to their swimming-feet, and were in the habit of resorting to shallow water for the purpose of incubation.

The above remarks apply more especially to R. Grenvillensis. I can speak with less confidence of Professor Hall's species; but the only specimen which I possess of the R. bilobatus of New York, differs from the Grenville specimens only in the proportions of length and breadth; as might be expected, if, as is probably the case, it is the track of a different species. My bilobate impressions from Nova Scotia have been produced by a small animal; perhaps the little species of Phillipsia which occurs in the same formation. Mr. Salter's Arenicola from the Longmynd wants the transverse markings, and the impressions are somewhat separate, so that they may be of a different character from the others. I think it quite likely, however, that the more elongated species of Rusophycus, in the Clinton of New York, may be casts of tracks of Trilobites, and I have long believed that a similar explanation will apply to some at least of the supposed fucoids known as Arthrophycus.

Taking this view of the origin of these singular objects, I would suggest to change the generic name of the Grenville fossil to Rusichnites. In such impressions it is scarcely to be expected that good specific characters can exist. I think it probable, however, that the Grenville specimens may indicate the presence of three species of Trilobites. Some of the smaller specimens are more elongated than the others, and have more numerous furrows. Other and larger ones are shorter and with fewer and more obtuse transverse furrows. A third variety is that referred to by Mr. Billings in his description, as having traces of lateral longitudinal furrows. These may in the meantime be included under R. Grenvillensis, Billings, as varieties (a), (b), and (c). (Figs. 1 and 2). My Nova Scotia specimens, though small, show little difference of character, but I would regard them as constituting a distinct species, under the name R. carbonarius. (Fig. 3).

A third species of Rusichnites has recently come into my possession, in a collection of fossils from the coal formation of Sydney, Cape Breton, sent to me by my friend Richard Brown, Esq. These impressions are, like the others, casts in relief, on a slab of sandstone. Each impression consists of the casts of contiguous rounded furrows, each about one-eighth of an inch in breadth, and crossed by curved undulations and striæ, in such a manner as to give the appearance of a pinnate leaf carved in high relief. At each side of these impressions, and about a tenth of an inch distant from them, are interrupted lines, in relief in the casts, and running parallel with the casts of the furrows. The whole has exactly the appearance of the track of the swimming feet and edges of the carapace of a small Limulus, about half an inch wide. The tracks have also the same tortuous character with those of the modern Limulus. Limuli have not yet occurred in the coal formation of Nova Scotia, though they occur in rocks of this age elsewhere; but from these tracks I infer that animals of this kind lived in the Sydney coal field, where their remains will probably hereafter be found. I propose for these impressions the name R. Acadicus, and will endeavor to figure them in the next number of the Naturalist.

ON THE GEOLOGY OF EASTERN NEW YORK.

By Professor JAMES HALL and Sir WILLIAM E. LOGAN.

Professor James Hall and Sir William Logan spent a few days together last summer in examining some points of the geology of Eastern New York, and propose to continue their examinations next season, when we may expect from them a detailed account of their results. Their principal object was to compare the rocks of that region with some of those of Eastern Canada; and I have now permission, in the absence of these gentlemen, to lay before this Society some of the results of this exploration.

The

The shales of the Hudson River group, which are seen for a considerable distance north and south of Albany, disappear a few miles east of the Hudson, and are succeeded by harder and coarser shales, sometimes red or green in color, and passing into green argillaceous sandstones. These various strata, which are associated with concretionary and shaly limestones, are now recognized as belonging to the Quebec group. The line of contact between this and the much more recent Hudson River group has nowhere been clearly seen in this region, but the two series are readily distinguished by their differences in color, texture, and hardness, differences which were formerly supposed to depend upon the partial metamorphism of the eastern portion, when this was looked upon as a part of the Hudson River group. green sandstones and conglomerates of Grafton Mountain, formerly looked upon as a portion of the Shawangunk conglomerate, are recognized as belonging to an outlying portion of the Sillery formation. This mountain Professor Hall had found in a previous exploration (1844-45) to have, at a point farther south, a synclinal structure, and it probably lies in three low synclinal axes. Sillery formation scarcely extends south of Rensselaer County. Canaan Mountain is also apparently synclinal, and, while limestones appear in the valleys on each side of it, consists chiefly of slates, the highest beds being a hard green sandstone, sometimes shaly, without any of the conglomerates of the Sillery; although boulders and angular fragments of these are found in the adjacent valleys. To the east of this, Richmond Mountain, in Massachusetts, presents in its upper portion a compact green slate, passing upwards into a harder rock similar to that of the summit of Canaan Mountain. To the southward, as far as Hillsdale, the

The

sparry limestones of the Quebec group appear in the valleys, while the hills are of slate. Proceeding thence westward towards the river, only the lower portions of the Quebec group are met with, until we come upon the rocks of the Hudson River group.

Washington Mountain is also of slate, flanked by limestone, all of the Quebec group, and is probably synclinal in structure. The valley to the south of the mountain exhibits limestones, apparently alternating with slates. Columbia and Dutchess counties appear to be mainly occupied by the shales of the Quebec group, with broad exposures of its limestones, until we approach the river to the westward, when the shales of the Hudson River group are met with, extending a considerable distance below the city of Hudson.

From Fishkill the explorers proceeded to Coldspring, crossing what Mather called the Mattewan granite, but which they found to be an altered sandstone. Soon after this they came upon the great gneiss formation of the Highlands of the Hudson, which continues beyond Peekskill. They failed to find the sandstone described by Mather as coming out at this place; nor was anything representing the Potsdam sandstone detected in approaching the Highlands from Fishkill, nor elsewhere along their northern limits. Near to Peekskill, in the valley of the creek, was found a low ridge of black slate, supposed to belong to the Quebec group, and a similar slate was observed along the north side of the Highland range, not far from the gneiss. The gneiss of the Highlands. presents all the aspects and characteristics of that of the Laurentian system, as seen in northern New York and in Canada.

Further examinations are necessary to determine the extension to the north-east of the Laurentian rocks of the Highlands, and also the succession of strata to the south-east of them. The recognition of the Sillery and of the Quebec group in this region are great and important facts for its geology, and not less so the identification with the Laurentian system of the gneissic district of the High. lands, to which the interesting mineral region of Orange county and the adjacent parts of New Jersey doubtless belongs. This conclusion, although opposed to the views of Mather and Rogers, who looked upon the crystalline rocks of the latter region as altered Lower Silurian strata, is in accordance with the older observations of Vanuxem and Keating, and with the more recent ones of Professor Cook, according to all of whom the gneiss and crystalline limestones of Orange County and of New Jersey underlie unconformably the Lower Silurian strata.

T. S. H.

370

NATURAL HISTORY SOCIETY.

The first monthly meeting of the Society for the Session 1864-65 was held at its rooms on Monday evening, September 26th, Dr. Dawson, President, in the chair. A large number of donations were announced:

TO THE MUSEUM.

Blackburnian warbler (Dendroica Blackburnia) and the blackthroated green warbler (Dendroica virens), shot near Montreal, and presented by Mr. W. Hunter. A large collection of English beetles, from W. M. S. D'Urban, Esq. A fine series of Canadian insects, of all orders, from Messrs. John B. Goode, C. Foley, R. J. Fowler, and Jas. Ferrier, jun. Fossils and recent shells from Prof. Dana (Newhaven), Dr. Hubbard (Staten Island), E. Seymour (New York), and C. Hart. Also a number of single specimens of interest, but which we cannot particularize from want of space. The donations to the Library were also numerous.

NEW MEMBERS.

Prof. R. Bell was elected a corresponding, and G. W. Simpson, Esq., an ordinary member of the Society.

PROCEEDINGS.

The first paper (On Rusophycus Grenvillensis, Billings) was then read by Principal Dawson. This paper is printed in the present number.

Mr. Billings read a paper, "On a remarkable specimen of Asaphus Platycephalus." The principal point of interest in this communication was that the author claims to have discovered what the legs of trilobites were like. The structure of the upper part of these remarkable fossils, so familiar to the student of the older fossiliferous rocks, has long been known to naturalists. Dr. Buckland, in his Bridgewater treatise, has described the microscopic details of the eyes of these curious crustaceans, which organs are not unfrequently preserved in the rocks,—and has fully illustrated their complex, compound character. But until now, the only portion of the under surface known was the part containing the mouth. This organ is situated in a plate on the under surface of