Notes on the Post-pliocene Geology of Canada, &c

Abstract

THESE “Notes,” which are reprinted from the Canadian Naturalist, cannot fail to interest European glacialists. Especially valuable for purposes of comparison are the detailed notes on the fossils obtained from the glacial beds. The lists include in all about 205 species, distributed as follows:—Radiata, 24; Mollusca, 140; Arti-culata, 26; Vertebrata, 5. All these, with three or four exceptions, may be affirmed, says the author, to be living northern or southern species. Moreover, the fauna of the older part of the Canadian glacial deposits is more Arctic in character than that of the modern part. It would thus appear that since the accumulation of the boulder-clay a gradual amelioration of climate has taken place; but the change from Arctic conditions has evidently been less decided on the west than on the east side of the Atlantic. Dr. Dawson's conclusions regarding what we may term the physics of the glacial epoch will probably meet with less acceptance than his palasontological results. He considers the Erie-clay described by Whittlesey, Newberry, and others to be of marine, and not of fresh-water origin, as these authors believe. But his reasons for this opinion can hardly be considered satisfactory. When an extensive deposit of fine clay, after having been examined over a wide area, is found not only to be totally destitute of marine organisms, but to contain quantities of drift-wood, and to have associated with it beds of peat and an old soil containing tree roots, the probabilities are that the clay-beds are of fresh-water origin. Besides, if we are not mistaken, fresh-water shells have been got in the Erie clay. That much-vexed question, the origin of boulder-clay comes in for some discussion in these “Notes,” the author inclining to think the deposit is marine. It is somewhat significant, however, that the boulder-clay is only fossiliferous in the lower part of the St. Lawrence river; further inland it has not been observed to contain fossils. From the author's description of the boulder-clay as seen at low levels in Canada, we think that deposit more closely resembles some of the maritime fossiliferous stony clays of Britain than our Till or lower boulder-clay. Dr. Dawson seems to have satisfied himself that the “real cause” of the excavation of the American lakes “was obviously the flowing of cold currents over the American land during its submergence.” He also thinks that “the fiords on coasts, like the deep lateral valleys of mountains, are evidences of the action of waves, rather than that of ice.” No glacialist, as far as we know, holds the extravagant belief that fiords have been cut out by ice. They are undoubtedly submerged valleys, and were hollowed out by streams and other atmospheric influences in ages long anterior to the glacial epoch. But however much we may differ from Dr. Dawson in some of his conclusions, there can be no doubt that he has added very considerably to our knowledge of American glacial deposits, and we cordially recommend the perusal of his “Notes” to our geological readers.

Notes on the Post-pliocene Geology of Canada, &c.

By J. W. Dawson (Montreal: Mitchell and Wilson, 1872.)