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 . Yet, even so,there are frequently floods in the lower part of the valleywhich reach a height of thirty or forty feet above presentlow water mark. But at the time of the greatest extent ofthe ice-sheet the drainage of not far from 250,000 squaremiles of ice covered area found its way into the Middle Mis-souri. For a considerable time towards the close of
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 . Yet, even so,there are frequently floods in the lower part of the valleywhich reach a height of thirty or forty feet above presentlow water mark. But at the time of the greatest extent ofthe ice-sheet the drainage of not far from 250,000 squaremiles of ice covered area found its way into the Middle Mis-souri. For a considerable time towards the close of theglacial epoch the ablation of this ice would, at a moderateestimate, amount to ten feet per annum over this wholecontributory surface. This would furnish 500 cubic miles ofadditional water to be carried off through the lower portionof the river channel during each summer between April andNovember. An examination of the lower channel shows thatat Hermon twenty-five miles below the mouth of the OsageRiver where it joins the Missouri the passage between rockybluffs 300 feet high is barely two miles wide. Mathematicalcalculations will show that it would require ninety-six daysfor a current two miles wide and two hundred feet deep, flow-. o >, t. o O — ?J a?- o -J a^ > ai3 •^^ OS -^ « » 3 •g_oo o 4^ +^ O CI — a cS Oi a o ao aj -3t>oj O tH El ?<J DRAINAGE OF THE GLACIAL PERIOD. 321 ing at the rate of three miles an hour, to carry off this surplusdrainage of 500 cubic miles accumulating each summer. If it should be supposed that the current would be muchfaster than three miles an hour, it is proper to note thatfrom the known facts about the northerly depression of theland during the latter part of the glacial period it is extremelyprobable that the gradient of the stream was very muchless during the time of these floods than it is now. Further-more, the gradient of the stream was much diminished by theflooded condition of the Mississippi into which the Missour
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Keywords: ., bookauthoruphamwarren18501934, bookcentury1900, bookdecade1910
