The ice age in North America and its bearing upon the antiquity of man5th edwith many new maps and illus., enland rewritten to incorporate the facts that bring it up to date, with chapters on Lake Agassiz and the Probable cause of glaciation . for-ests and vegetable growth would soon have spread over themarginal belt from which the ice had retreated, and, upona readvance, these would be overwhelmed and covered witha new stratum of glacial deposition. In case of some ofthe peat beds, it is probably necessary to suppose that theywere formed where they are, and are really interglacial; but,in cas
The ice age in North America and its bearing upon the antiquity of man5th edwith many new maps and illus., enland rewritten to incorporate the facts that bring it up to date, with chapters on Lake Agassiz and the Probable cause of glaciation . for-ests and vegetable growth would soon have spread over themarginal belt from which the ice had retreated, and, upona readvance, these would be overwhelmed and covered witha new stratum of glacial deposition. In case of some ofthe peat beds, it is probably necessary to suppose that theywere formed where they are, and are really interglacial; but,in case of many of the fragments and logs of wood foundin the glacial deposit, we are not compelled to suppose aninterglacial origin. Wood will stand transportation in theground-moraine almost as well as bowlders, and it is by nomeans certain that much of the timber found in the till may * See Chamberlin, Geology of Wisconsin, vol. i, chap, xv, especiallypp. 271-291 ; Driftless Area, pp. 211-216; N. H. Winchell in Proceedingsof the American Association for the Advancement of Science, vol. xxiv, 1875,pp. B, 43-56; Geology of Minnesota, vol. i of the Final Report, pp. 363et seq. ; J. S. Newberry, Geological Survey of Ohio, vol. ii, pp. Fiu. 14S.—Perpendicular section of till at Oxford. Ohio, showing a niece of wood threeinches in diameter projecting from tlie face. This has evidently oeen trangportid inthe till like a bowlder. The .section is about fifty feet; portion shown, about fiflinifeet, tin middle. (United States Geological Survey ) (Wright.) 578 THE ICE AGE IN FORTE AMERICA. • not have belonged to the original forests which covered thecountry in front of the first sheet of advancing ice. Theselogs may have been picked up like the bowlders, and trans-ferred to the south a long time after their original deposi-tion. Thus, it may be that the forest-beds near the mar-gin of the glaciated area are of more recent origin than thosesome distance back, since the ice i
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