This equivalency and the disturbance which brings the Quebec group to the surface (the course of which disturbance has already been given in the communication addressed to Mr. Barrande) suggest the following considerations.

From the occurrence of wind-mark and ripple-mark on closely succeeding layers of the Potsdam sandstone where it rests immediately upon the Laurentian series, we know that this arenaceous portion of the formation must have been deposited immediately contiguous to the coast of the ancient Silurian sea, where part of it was in some places even exposed at the ebb of tide. No want of conformity is known to exist between the Potsdam and Calciferous formations, and the Quebec group being of Calciferous age and 7000 feet thick, it follows that during the Potsdam period, while the typical sands of the formation were on a level with the surface of the sea, there must have existed a depth of water of at least 7000 feet over the area on which were subsequently deposited the strata of the Quebec group.

As constituting the great metalliferous formation of the continent this group is traceable under various designations from Gaspé to Alabama, thence sweeping round on the west side of the Mississipi through Kanzas to Lake Superior, without suffering any diminution in its volume, thus forming the measure of a deep sea in the course indicated, and probably still farther to the Arctic ocean. Within this line northward in so far as Canada is concerned, we find a marginal outcrop of these rocks of only a few feet in thickness on the north coast of Lake Huron from Lake Superior to Lacloche. Including the Potsdam sandstone they are altogether absent between Lake Huron and the neigh bourhood of Kingston. In the area between the Laurentide and Adirondac Mountains, from a line between Lake Ontario and the Lac des Chats eastward to Lake Champlain on the one hand and the St. Maurice on the other, the united thickness of the Potsdam, Calciferous and Chazy formations scarcely attains 1000 feet. With the exception of a small mass of the Potsdam sandstone at St. Ambroise near Quebec, we have no evidence of a marginal outcrop of the formation between the St. Maurice River and the Mingan Islands, while a similar outcrop of the Calciferous and Chazy formations has not been observed from the longitude of Lake St. Peter to the same group of islands; in these islands themselves the thickness of the three formations does not exceed

500 feet, but beyond this we are not yet sufficiently acquainted with the Lower Silurian rocks to make any statement.

From these facts however it would appear probable that during the Potsdam period the older rocks which formed the coast of the Lower Silurian sea extended under comparatively shallow water south-eastwardly from the St. Lawrence and Ottawa to the position of the fault which brings the Quebec group to the surface between Gaspé and the Mohawk river, and south-westwardly from a line between the Mohawk and Lake Superior as far as Alabama. From this shallow area they descended quickly into deep water all around, thus constituting a subaqueous promontory from the so-called azoic rocks of the north-east, and forming with them what Professor Dana I believe has termed the nucleus of the North American continent.

But though the volume of the Quebec group makes it apparent that over the area occupied by it and the subjacent black shales, there must during the Potsdam period have existed a deep sea, it is yet to be remarked that many of the members both of the lower and upper parts of the group have by no means the character of deep sea deposits. To obtain the conditions required for the accumulation of the coarser members of the series, which commence near the bottom of the group, it must be supposed that about the beginning of the Calciferous period, a great continental elevation occurred, carrying the shallow water deposits of the Potsdam high above the sea and bringing the area at the base of the Quebec group comparatively near the surface. The successive coarse deposits of the group indicate a subsequent gradual subsidence at unequal intervals until the early shallow water strata were again submerged, to be first partially covered over by deposits of the Chazy formation, and then almost universally by those of the Birdseye, Black River and Trenton.

In this way may be accounted for the break which occurs in the succession of life between the Calciferous and Chazy, in the development of the latter formation between the Allumette Island and Montreal, as well as among the Mingan Islands; and the break in the succession of deposits between the Potsdam and Birdseye at St. Ambroise, between the Laurentian and Birdseye from the north shore of Lake Huron to Kingston, in the vicinity of Bay St. Paul and of Murray Bay, and in Lake St. John on the Saguenay.

The break in the succession of life between the Chazy and Birdseye, is not so great as that between the Calciferous and Chazy. It is not yet quite certain that in Canada a single species passes upwards in the latter case, while in the former, the proportion which does so is about one-sixth. It seems to be in accordance with this, that we have evidence of a somewhat sudden submergence for the introduction of the Birdseye and Black River group, and a somewhat rapid accumulation of its deposits. Where these rest upon the Huronian and Laurentian series, the beds of contact are often composed of angular fragments of the rock beneath, and it frequently happens that the surface on which these beds rest, is rough and uneven, broken into sharp projecting ledges and deep fissures, which have been filled up and covered over by the deposits in question, before sufficient time had elapsed to permit the asperities of the bottom to be worn to a smooth surface.

An instance in illustration of this occurs on the Snake Islands, west of Lacloche in Lake Huron, where the Birdseye and Black River group rests on the quartzites of the Huronian series, and the lowest bed of the group is made up of angular fragments of the quartzites cemented together by the fossiliferous limestone; there is another at Marmora, where the same group, supported by Laurentian rocks, fills up deep angular cavities in the surface. Dr. Dawson has pointed out a striking instance of the phenomena at Hog Lake, in Huntingdon; others occur at Sloat's Lake in Loughborough and places adjacent, as well as at Kingston Mills, and the same phenomena are observable in the neighbourhood of Murray Bay.

As an instance of the probably rapid slope with which the bottom of the Lower Silurian sea descended from shallow to deep water during the Potsdam period, in the neighbourhood of Quebec, we see that the surface of the gneiss now supporting the Trenton formation at the Falls of Montmorency, must have been as much as 7000 feet above that under the Island of Orleans, where the Quebec group makes its appearance, while the distance between the two positions does not exceed a mile and a half; this would give a slope of nearly forty-five degrees, and perhaps it would not be extravagant to take it as more or less typical of the slope on the whole line to Alabama.

As the black shales and limestones subordinate to the Potsdam and the deposits of the Quebec group accumulated, the

edges of the strata would abut against this slope, and ultimately both they and the early shallow water deposits on the higher terrace would be covered over by the Birdseye, Black River, Trenton, Utica, and Hudson River formations, as represented in the accompanying diagram, (fig. 3.)

Limestones (Birdseye Black River and Trenton.)
u, Dark gray shales and sandstones, (Hudson River.)
L', At the level of the sea during the Potsdam period.
Black Shales (Utica.)

at the commencement of the Calciferous.

Without enquiring into the origin of the forces which have

produced the corrugations of the earth's crust, we may suppose that if a sufficient lateral pressure were applied to strata thus accumulated and arranged, there would result a set of parallel folds and overlaps, running in a direction at right angles to that of the pressure, with prevailing overturn dips in the direction of movement; the greater strength, however, of the solid crystalline gneiss in this particular case, offering more resistance than

the newer strata, would cause a break coinciding with the inclined plane at the junction of the gneiss and Quebec group; the strata of this group pushed up the slope would raise and fracture the strata of the formations above, and be ultimately forced into an overlap of that portion resting on the higher terrace, after probably thrusting over to an inverted dip that part of the upper beds with which they came in contact. The strata of the upper terrace, relieved from pressure by the break, would remain comparatively quiescent, and thus the limit of the more corrugated area would coincide with the slope between the deep and shallow water of the Potsdam period. But the resistance offered by the gneiss would not merely limit the main disturbances, it would probably also guide or modify in some degree the whole series of parallel corrugations, and thus act as one of the causes giving a direction to the Appalachian chain of mountains.

REVIEWS AND NOTICES OF BOOKS.

Life on the Earth, its Origin and Succession, by JOHN PHILLIPS A.M., LL.D., F.R.S., Late President of the Geological Survey and Professor of Geology in the University of Oxford.

This volume contains the substance of the Bede Lecture, delivered at Cambridge, in May 1860. Like everything that Prof. Phillips does, it is clear, accurate and scholarly. It gives in small compass and in a manner intelligible to all, a summary of the facts known to Geology respecting the introduction and order of succession of life on the earth, without any of the exaggeration and looseness of statement too common in popular books. It can be safely recommended to every one desirous of knowing the present state of this subject, and its bearing on the Darwinian doctrine of the origin of species by natural selection. The work might afford many interesting extracts, but we content ourselves with copying the Author's concluding reflections, which are full of great truths, and with recommending our readers to procure the work for themselves.

"These various speculations on the subject of Fossil plants and animals, and the origin and progress of life, may perhaps, to the student of exact science, appear little more than the chase of a phantom, a wandering after unattainable truth. There is, however, something seduc