p. 274

285

Remarkable ridges

taken place in the region of these Lakes? A depression of the country about the Niagara river of one hundred and eight feet and an elevation of the northern portions of Illinois of only forty feet would produce all the changes here indicated. This change of level would reduce Lake Erie to the original level of Lake Michigan and at the same time elevate the latter sufficiently to turn back its waters into their present course.

The description of Lake Michigan and the interesting facts connected with it would not be complete without a notice of the remarkable succession of sand ridges between Chicago and Michigan City, described by Prof. G.U. Shepard.

"On drawing near the head of the lake, by the way of the road to Michigan City we find the surface of the prairie invaded far inland by a succession of ancient beaches formed with the utmost regularity as to width and height as well as conformity to the existing shore of the Lake. Leaving Chicago the road for about fifteen miles is on the beach [of]

159