A. From a Mound near Albany, Whiteside Co., Ill., in the Museum of the Davenport, Iowa, Academy of Science.

B. From a Mound in Schuyler Co., Ill. (Author's collection.)

Lawrence, as far up as Lake Erie, remained filled with ice long after the water-sheds farther west were freed from their gradually retreating glaciation. Consequently, the waters of Lake Michigan rose to the height of the old Chicago beach lines, and then escaped, in great volume, through the valley of the Illinois river. In course of time the St. Lawrence ice barrier was removed, thereby restoring the eastern outlet of the Lakes, lowering Lake Michigan to its present level, and relieving the Illinois river valley of its immense enforced drainage.

For many centuries during and after the Ice Age, Illinois was a barren desolation in which terrestrial life was impossible. The great pachyderms, the mastodons and mammoths, that for ages had held undisputed sway over forest and plain, together with the entire primal fauna and flora, were swept away and buried in the mass of detritus left by the departed ice, commensurate in extent with the ice-covered area. That crushed,

ground, water-worn material-classified by geologists as "mantle rock," "boulder clay, or till," and "glacial drift, or loess"-deposited from 1 to 450 feet in thickness, wrought vast changes in the physiography of our State by filling river beds and valleys, diverting streams in other courses, and giving the average surface its present topographical flatness." Within ten or twelve hundred centuries following the last recession of the ice fields, the process of transforming Illinois from a lifeless solitude to a theatre of teeming animation, by the agencies of rain and frost, wind and sunshine, was slowly accomplished. Life, both animal and vegetable, first appeared in the rivers and lakes. Vegetation cautiously creeping landward, spread, flourished, and, by succession of growth and decay for ages coated the drift sands and clays with productive soil.

5 See the very interesting and instructive monograph by Prof. Harlan H. Barrows; entitled, "Geography of the Middle Illinois Valley," published as Bulletin 15 of the Illinois State Geological Survey.