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 . over the northernhemisphere and its subsequent return to the ocean there isbrought to light a force of such incalculable power affectingthe elevation and depression of the land that the effects areentirely abnormal to our present experience. We cannotreason back from the rate of present changes to that ofthe Glacial Period. (2) Again, we are never at lib
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 . over the northernhemisphere and its subsequent return to the ocean there isbrought to light a force of such incalculable power affectingthe elevation and depression of the land that the effects areentirely abnormal to our present experience. We cannotreason back from the rate of present changes to that ofthe Glacial Period. (2) Again, we are never at liberty to lose sight of the factthat a long period of disintegration of the rocks over the gla-ciated region preceeded the ice age. The rocks over thatregion were then rotted to a great depth as they are now inthe region south of the ice limit. This furnished an immenseamount of oxidized nuiterial for the first grist of the glacialmill, and that was spread vridely over the southern marginof the glaciated area. CHAPTER X. GLACIAL EROSION AND TRANSPORTATION. The extent of glacial erosion is a hotly contested class of writers has gone to the extreme of attributingalmost all the erosion of the higher latitudes to glacial action,. Fig. 70.—Canon of the Colorado. Stream-erosion in a dry climate. (Newberry.) wliile another class has scarcely allowed any eroding powerto glacial ice. in comparison with that of running considering the relative importance of these agencies,
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