derable height above the level of the lake may be attributable to a gradual elevation of the land or to a subsidence of the water. The last hypothesis seems the most tenable, since the first would involve a local upheaval only, and an inclination of the plane of the terraces at variance with their apparent horizontality. Should further researches prove the existence of terraces or other indications of old beaches on the western margin of Lake Huron corresponding in height with those discovered along the eastern shore, the supposition that the level of the water has been lowered by the wearing away of some barrier will be strongly supported; and if this be allowed as a reasonable explanation for these geological monuments, we have then, by drawing contour lines coinciding with their level the means of discovering the probable position of this barrier. From all that I can learn regarding the relative levels of the country these lines would pass over the peninsula between Lakes Huron and Erie at some distance inland from the River St. Clair and would if continued eastward along the shores of Lake Erie fall within the summit of the neck of land through which the chasm of the Niagara River is cut."

The northern part of the Township of Nottawasaga is situated on the extensive sandy plain above alluded to, which was no doubt formerly covered by an extension of Georgian Bay to the south-eastward. The whole has a general slope up from the bay, but here and there a ridge of gravel or coarser sand interrupts its general uniform aspect. Hurontario Street, running from Collingwood Harbour almost due south through the township, was carefully levelled by Wm. Gibbard, C. E., and it appears from his profile section of the street, that from Collingwood to the north side of the Pretty River at the Village of Melville or Nottawa Mills, a distance of two and a half miles, the ground rises very regularly from the edge of the water to an elevation of 138 feet, or at the rate of about 55 feet per mile. At the Pretty River a change begins both in the character of the surface and in the rate of its inclination, which continues regularly for three and a half miles further at 47 feet per mile. Thus, at a distance of six miles from the present shore, the surface has attained an elevation of more than 300 feet above the level of the lake; beyond this it rises irregu larly and much more rapidly. It is evident that the bank of sand and gravel on the north side of the Pretty River continued for a long time to be the shore of the lake. The layers of sand and gravel are arranged exactly as on a modern beach, and among them I noticed several thin irregular beds of a light grey or white colour, composed principally of carbonate of lime. In the cutting through the top of this ridge the common land shells Helix alCAN. NAT.

VOL. VI.

bolabris, H. tridentata, H. Sayii, H. alternata, and H. fuliginosa were collected, at from three to four and a half feet below the surface.

About a mile south of Collingwood, a shallow cutting for the road, exhibits the arrangement of the beds of sand and gravel, which at the base of the exposure dip southward at an angle of 35° and are overlaid to the surface by unconformable horizontal layers. Here, from the surface to a depth of three feet, Planorbis trivolvis and Helix fuliginosa, H. tridentata and H. thyroi des? were found. The summit of this rise is 78 feet above the level of the lake, and from its plotted section appears to have been thrown up by the waves when the edge of the lake ran along the base of its northern slope.

There are a few specimens of Melania conica in the Geological Museum, from a railway cutting in sand near Collingwood.

The greater part of the town of Owen Sound is built on a loose deposit of gravel and fine sand at the head of a long arm of the Georgian Bay of the same name. The flat formed by this deposit slopes gradually up from the head of the bay towards the falls of the Sydenham River, which has cut its way through it, and is bounded on either side by terraces of Silurian limestone or marl. Fresh water shells were observed in abundance wherever a section of the sand was exposed, and also, in one place, Helix alternata the most abundant land shell on the shores and islands of Lake Huron.

The following species were most central part of the town.

collected in different places in the One of these, on the bank of the river was about nine feet above the level of the lake; the others appeared to be a little higher.

About a mile south from the mouth of the river, or following the upward course of the valley, the road is cut through a slight elevation in this lacustrine deposit and here also fresh water shells were found embedded in the sand, but neither the species nor individuals

were so numerous as in the same deposit nearer the head of the bay. I had no means of ascertaining the elevation of this spot above the lake, but it seemed to be more than 30 feet and the shells bore evidence of great antiquity.

The terraces before alluded to as bounding this flat are capped with fine sand and their summits appeared to exceed 80 feet above the level of the lake. They are well marked and extend for miles along each shore of the Sound. At Peiett's Harbour, or the French Village on the west side of Owen Sound and about twelve miles from the town of the same name, two steep and very well marked lake terraces rise, one above the other, near the water's edge. They are both composed, as far as I examined them, of shingle mixed with a little silt. The summit of the upper one appeared to be about 100 feet above the lake and is in all probability the continuation of the upper terrace running round the head of the Sound, while the lower one corresponds to that on which the town is built.

When Lake Huron was at a sufficient elevation to form the higher of these terraces, it was probably connected by a wide expanse with Lake Erie, which is also proved to have stood at this high level from the fact of a ridge holding fragments of decayed wood and fresh water shells, running along its southern side at an elevation of 150 feet above its present level.

MONTREAL, Feb. 4th, 1861.

ARTICLE V.-Professor Guyot on the Physical Geography of the Appalachian Mountain System.

The great Appalachian backbone of Eastern America though much visited in some of its peaks by tourists, penetrated by many roads, and stretching through the midst of a civilised country, has hitherto been little known to Physical Geographers in its details. Prof. Guyot has made it a special subject of study since his arrival in America; and since 1849 has devoted his summer excursions to the accurate barometrical measurement of its elevations at various points throughout its whole length. The results, including details of the methods of observation employed, and a table of the heights of all the principal peaks, table-lands and gaps, are published in Silliman's Journal; from early sheets of

which kindly forwarded to us, we extract the following general conclusions as to the physical structure of the chain.

"The upheavals of ancient rocks which constitute this well connected physical structure, for which, as a whole, it is proper to retain the common name of the Appalachian system, extend in an undulating line thirteen hundred miles in a mean direction of N. E. to S. W., from the promontory of Gaspé upon the Gulf of St. Lawrence to Alabama, where the terminal chains sink down and are lost in the recent and almost horizontal strata of the cretaceous and tertiary formations which cover the greater portion of the surface of this state. This long range of elevations is composed of a considerable number of chains, sensibly parallel to each other, occupying more particularly the eastern part which faces the ocean, and of an extended plateau which prevails towards the west and northwest and descends gradually towards the inland valleys of the St. Lawrence, the lakes Erie and Ontario and the Ohio River.

The base on which this large belt of mountains rests, and which may be considered as bounded by the Atlantic Ocean on one side and by the Ohio and St. Lawrence Rivers on the other, is formed, in the east, by a plain slightly inclined towards the Atlantic. The width of that plain, in New England, does not vary much from fifty miles. Near the mouth of the Hudson, however, in New Jersey, it nearly disappears, but gradually increases towards the south to a width of over two hundred miles. Its elevation above the sea, at the foot of the mountains, is in New England, from 300 to 500 feet. From the neighborhood of the bay of New York, where it is nearly on a level with the ocean, it rises gradually towards the south to an altitude of over 1000 feet. On the west the table-lands which border upon the Ohio River, and which may be considered as the general base of the system, preserve a mass-elevation of a thousand feet or more, in the thickness of which the river bed is scooped out to the depth of from 400 to 600 feet, thus reducing the altitude of the Ohio River full one-half from that of the surrounding lands.

The vast belt of the Appalachian highlands forms the marginal barrier of the American continent on the Atlantic side, and determines the general direction of the coast line, which in general, runs parrallel to the inflections of its chains with remarkable regularity. This system, composed of a series of corrugations tolerably uniform, does not, like the Alps, or the other great systems of fracture, have a central or main axis, to which the secondary chains are subordinated. But it is properly compared to the system of the Jura, for it is composed like that of a series of long folds, or chains, which run parallel to each other, often with great regularity. In the same part of the system the general height of the chains is sensibly equal and their summits show neither many nor deep notches. In the middle region, especially in Pennsylvania and New Jersey, they present the appearance of long and continuous walls, the blue summits of which trace along the horizon a uniform line

seldom varied by any peaks or crags. In the extreme northern and southern portions, however, this character is considerably modified. There the system loses very much of its uniformity and its physical structure becomes far more complicated; the form of simple parallel ridges almost entirely disappears.

There is one feature of the Appalachian system which distinguishes it from the ranges of the Jura; it is the well marked division into two longitudinal zones of elevation, one turned towards the shores of the Atlantic, in which the form of parallel chains just spoken of predominates, and the other turned towards the interior, which is composed of elevated and continuous plateaus, descending from the summit of their eastern escarpment, in the centre of the system, in gentle stages towards the basins of the lakes and the valley of the Ohio. Occasionally minor chains, very little elevated from their base, wrinkle the surface of the table-lands. Their parallelism with those of the eastern mountainous zone shows that they are but the last undulations due to the action of the same forces which have upheaved and folded that region, and which have raised at the same time, the mass of these more uniform plateaus. Thus when from any point we traverse the Appalachian system from the Atlantic, we encounter first a plain more and more undulated and gradually ascending to the foot of the mountains; then a mountainous zone with its ranges parallel and its valleys longitudinal; at length a third zone of uniform plateaus slightly inclined towards the northwest, and cut with deep transverse valleys.

Another feature not less conspicuous characterizes the region of corrugations properly so-called. This is a large central valley which passes through the entire system from north to south, forming, as it were, a negative axis through its entire length. This is what Mr. Rogers calls the Great Appalachian valley. At the north it is occupied by lake Champlain and the Hudson river; in Pennsylvania it bears the name of Kittatinny or Cumberland valley. In Virginia it is the Great valley; more to the south it is called the valley of East Tennessee. At the northeast and at the centre its average breadth is fifteen miles; it contracts in breadth towards the south, in Virginia, but reaches its greatest dimensions in Tennessee where it measures from fifty to sixty miles in breadth. The chain, more or less compound, which borders this great valley towards the southeast is the more continuous and extends without any great interruption from Vermont to Alabama. In Vermont it bears the name of Green Mountains, which it retains to the borders of New York; in the latter State it becomes the Highlands; in Pennsylvania, the South Mountains; In Virginia the Blue Ridge; in North Carolina and Tennessee the Iron, Smoky, and Unaka Mountains. On the northwest of the great valley between the latter and the borders of the plateau parallel there extends a middle zone of chains separated by narrow valleys, the more continuous of which is the range which bounds the central valley. This zone has a variable breadth in different parts of the system, and the number of chains which compose it is by no means uniform throughout.