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 . dent T. C. Chamberlin. arearranged in lines, and their longer axes invariably lie parallelto the movement of the ice. In some localities, especially : * Geology of Connecticut, 1842, pp. 256, 461, 479, 485. t Transactions of the New York Academy of Sciences, vol. i, 1882, p. 77. DRUMLINS. 287 in Dodge and Jefferson counties, these are mainly replaced
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 . dent T. C. Chamberlin. arearranged in lines, and their longer axes invariably lie parallelto the movement of the ice. In some localities, especially : * Geology of Connecticut, 1842, pp. 256, 461, 479, 485. t Transactions of the New York Academy of Sciences, vol. i, 1882, p. 77. DRUMLINS. 287 in Dodge and Jefferson counties, these are mainly replaced bylong parallel ridges, sometimes several miles in lengtli. withcorresponding linear marshes interspersed. These correspondaccurately to the direction of the ice-motion. * According toMr. Upham, drumlins are not found in the abundant drift ofMinnesota. A few examples are mentioned for Pennsylvania,near its western border, by Professor Lewis, f In endeavoring to account for this class of hills, tMO or three facts are of special importance: material of _wliich^th€y-are CA^niposed is very heavy and compact—almost ^s^ieavy apdcoinpact, indeed, as ice. Such masses could not have been shoved along bodily beneath the ice.~Tn fact,. Fi(i. 02.— in liolistown. N. H. (Hitchcock.) there would seem to be no reason why they might not resistthe erosion of the glacier almost as well as many of the softerrocks did, especially when we remember that the pressure ofthe ice on the bottom need not have been uniform, buT^greater in some places than in others. 2. There are manyindications that these hills were formed by accretion underthe ice, there being, as Mr, Upham has shown, a tendency toJaraination or coarse glacial stratification in the stracture oF * Geology of Wisconsin, vol. i, 1883, p 283. f Second Geological Surrey of Pennsylvania, Z, pp. 29, 188. 288 THE WE AOE IN NORTH AMERICA. the hills.* 3. They are not characterized by surfaces are remarkably s
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