. Soil physics and management. e inch for each hundred feet in thickness, enabled it towear down hills and fill valleys, especially if they extended nearlyat right angles to the direction of the movement. Otherwise itmight deepen and broaden them, but on the whole its effect has beento leave the country more nearly level than before. Many regionshave been transformed from hilly areas of low agricultural valueto undulating or rolling lands well adapted to agriculture. The icein its movement southward picked up large quantities of detritusof all kinds and sizes and ground it into fine material f
. Soil physics and management. e inch for each hundred feet in thickness, enabled it towear down hills and fill valleys, especially if they extended nearlyat right angles to the direction of the movement. Otherwise itmight deepen and broaden them, but on the whole its effect has beento leave the country more nearly level than before. Many regionshave been transformed from hilly areas of low agricultural valueto undulating or rolling lands well adapted to agriculture. The icein its movement southward picked up large quantities of detritusof all kinds and sizes and ground it into fine material fitted to formsoils. Much of this material was carried from 400 to 1,000 milesor more and during its transportation boulders (Fig. 34) and gravelwould rub and grind against each other and against the rock sur- GLACIAL OR ICE-LAID DEPOSITS 43 faces over which they moved (Fig. 35), producing immense quan-tities of rock flour. The whole glacier was an immense mill thatwas slowly grinding rocks into powder. This rock flour was lib-. FiG. 35.—Glacial grooves or striae ou lock Miilaic. i\oilhern Ohio. (From Elements ofGeology, Copyright 1911, by Eliot Blackwelder & Harlan H. Barrows. American Book Co.)
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