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 . of glacial icein the transportation of solid material, we speak first of thatcarried upon the surface. Apparently there is scarcely any * Arctic Explorations, vol. ii, p. 148. 236 THE ICE AGE IX NORTE AMERICA. limit to the size of the fragments of rock which can betransported upon the back of a glacier. Nor would thereseem to be amy definable limit to th
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 . of glacial icein the transportation of solid material, we speak first of thatcarried upon the surface. Apparently there is scarcely any * Arctic Explorations, vol. ii, p. 148. 236 THE ICE AGE IX NORTE AMERICA. limit to the size of the fragments of rock which can betransported upon the back of a glacier. Nor would thereseem to be amy definable limit to the distance through whichthese masses of rock can thus be carried, except as there is alimit to the movement of the ice itself. In walking out onthe smooth surface of the eastern part of the Muir Glacier,it was not uncommon to encounter, miles away from anymountains, cubical blocks of stone as much as twenty feetin their several dimensions, which, with countless others ofsmaller size, united to form a medial moraine. Slowly butsurely these great bowlders have been brought to their pres-ent position, and slowly but as surely they are moving on tothe front of the glacier, where, in due time, they will bedeposited in the terminal Fig. 72.—Vessel Rock, a glacial bowlder in Gilsum, N. H. (C. H. Hitchcock.) The summary of facts published by President Hitch-cock many years ago may fitly serve as an introduction tothe more detailed account to follow. In this, after remark-ing upon the great size of single bowlders, he illustrates theremark by the following examples : The block called Pierre a Bot, near Neufchdtel, contains40,000 cubic feet. It has been transported from near Mar-tigny, more than sixty miles, across the great valley of Switz- GLACIAL EROSION AND TRANSPORTATION. 237 erland. Professor Forbes describes another bowlder in theAli^s, one hundred feet long and forty to fifty feet high ; alsoanother, sixty-two feet in diameter, containing 244,000 cubicfeet. In this co
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