Forest physiography; physiography of the United States and principles of soils in relation to forestry . Fig. iSo. — Positions of the Wisconsin ice lobes aboutthe Driftless Area. (Weidman, Wise. Gaol, Surv.). Fig. 181. — Relations of the drift sheets of Iowa and northern Illinois, i, Kansan; 2, Illinoian; 3, lowan;4, Early Wisconsin; 5, Late Wisconsin; 6, Driftless area; 7, course of the Mississippi River during theIllinoian glacial epoch. (After Leverett, U. S. Geol. Surv., and Calvin, Iowa Geol. Surv.) 1 W. F. Cooper, Water-Supply Paper U. S. Geol. Surv. No. 182, 1908, Plate II. 474 FOREST P
Forest physiography; physiography of the United States and principles of soils in relation to forestry . Fig. iSo. — Positions of the Wisconsin ice lobes aboutthe Driftless Area. (Weidman, Wise. Gaol, Surv.). Fig. 181. — Relations of the drift sheets of Iowa and northern Illinois, i, Kansan; 2, Illinoian; 3, lowan;4, Early Wisconsin; 5, Late Wisconsin; 6, Driftless area; 7, course of the Mississippi River during theIllinoian glacial epoch. (After Leverett, U. S. Geol. Surv., and Calvin, Iowa Geol. Surv.) 1 W. F. Cooper, Water-Supply Paper U. S. Geol. Surv. No. 182, 1908, Plate II. 474 FOREST PHYSIOGRAPHY surface features which also show the characteristic effects of country is here for the most part level, but it also presents longrolHng slopes rising from 300 to Soo feet above broad valleys. Themost important topographic elements are massive ridges or mesas due to preglacial erosion. The mesasare in many instances bordered orcrowned by long morainic ridgesrepresenting halts in the glacialadvance or retreat. The morainicmaterial is derived chiefly from theunderlying shales (Cretaceous),and is a compact clay whichalso contains erratic fragmentsand bowlders of crystalline ro
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectforestsandforestry
