In the following table I have endeavoured to represent to the eye the facts observed in the internal plain of the great Lakes, and in the marginal area of the Atlantic slope, with the mode of accounting for them on the rival theories of glacier ice and floating ice.

It will be observed that the theoretical views diverge with respect mainly to the Boulder-clay and the striation under the Erie clay, and to the cause of the erosion of valleys in the Pliocene land. I would merely remark, in addition to the considerations already advanced, that the occurrence of drift-wood in the Erie clay, and of sea shells in the Boulder-clay, are both most serious objections to the glacier hypothesis, reserving for the sequel a more full discussion of the rival theories.

While the marginal marine area strictly corresponds to the marginal areas of Europe, I have no distinct evidence that the internal plains and table lands of the old continent correspond in their formations to the internal lake area of America.

An interesting fact with reference to the Erie clay, stated in the Report of the Survey of Canada is, that these clays burn into

white brick, while the marine Leda clay burns into red brick. The chemical cause of this I have already referred to, but whether it implies that the inland clays are fresh-water, or only that they have been derived from a different material, is uncertain. The gray clays of the Hudson River series in Western Canada, might, according to Mr. Bell, have afforded such clays.

Under the theory of a glacial sea immediately succeeding the elevated Pliocene land, the great amount of decomposed rocks which must have accumulated upon the latter constitutes an important element in the estimation of the rate of deposit of the Erie and Boulder and Leda clays. It is also to be observed that this glacial sea might have had to scour out of the lake basins of Canada only the soft mud of its own deposition, the rock-excavation having apparently been in great part effected in the previous Pliocene period. On this subject I find that Dr. Sterry Hunt had, before the publication of Dr. Newberry already alluded to,* shown that not only channels but considerable areas about Lakes Erie and St. Clair had been deeply excavated in the paleozoic rocks and filled with Post-pliocene deposits. The Devonian strata, he remarks, "are found in the region under consideration at depths not only far beneath the water level of the adjacent Lakes Erie and St. Clair, but actually below the horizon of the bottom of these shallow lakes." He shows that around these in various localities the solid rocks are only met with at depths of from one to two hundred feet below the level of the lakes, while "the greatest depth of Lake St. Clair is scarcely thirty feet and that of the South-western half of Lake Erie does not exceed sixty or seventy feet, so that it would seem that these present lake basins have been excavated from the Post-pliocene clays, which, in this region, fill a great ancient basin previously hollowed out of the paleozoic rocks, and including in its area the Southwestern part of the peninsula of Ontario."

It would thus appear that in the Pliocene period the basin of the lakes may have been a great plain with free drainage to the sea. Whether or not it was afterwards occupied by a glacier, this plain and its channels leading to the ocean were filled with clay at the beginning of the Post-pliocene subsidence; and at a later date the mud was again swept out from those places where the Arctic current could most powerfully act on it.

(To be continued.)

On the Geology of South-western Ontario. Am. Jour. Sci. 1868.

ON THE PHYSIOGRAPHY AND GEOLOGY OF THE ISLAND OF GRAND MANAN.

BY PROF. L. W. BAILEY.

The Island of Grand Manan, near the entrance of the Bay of Fundy, though so long and so well-known for its picturesque scenery and from the richness of the surrounding waters as a fishing-ground for marine invertebrates, has received comparatively little attention at the hands of the geologist. Statements bearing more or less directly upon its geological structure have indeed appeared from time to time, but since the date of Dr. Gesner's first exploration of the island (in 1838) no examinations with a special view to the determination of that structure have been made until quite recently. The most discordant views have in consequence been entertained with reference to the age of its rock formations. A visit, of some four days duration, made during the summer of 1870, in pursuance of duties connected with the Geological Survey of Canada, having enabled me to examine a considerable portion of the island and to compare its rocks with those recognized upon the main-land of New Brunswick, I propose to give here some of the conclusions at which I have arrived.

The general form of the island of Grand Manan is that of an irregular elongated oval, of which the greater diameter is about fifteen and the shorter about seven miles. Its surface, for purposes of description, may conveniently be divided into two distinct regions, contrasted equally in their physical and in their geological features. Of these the westerly and more extensive tract, embracing more than two-thirds of the main island, has the character of a somewhat elevated plateau, traversed in a direction parallel to its length by a series of minor ridges and depressions, and exposing upon the western shore, which is remarkably uniform and entirely free from islands, a series of bold bluffs, varying from two to four hundred feet in elevation.* This plateau is for the most part well wooded (with birch, maple, beech, &c.,)

Among flowering plants observed on the island (August 22nd) were Asters and Solidagots of several species, Scutellaria galericulata, Potentilla fruticosa, Campanula rotundifolia, Epilobium angustifolium, Sedum rhodiola, &c.