Raised Beaches of Lake Michigan. 177 



RAISED BEACHES OF LAKE MICHIGAN. 



By frank LEVERETT. 



There are around the head of Lake Michigan several raised beach lines 

 and sea cliffs, the latter being eroded escarpments of the tall plains and 

 moraines. These have been discussed at some length by Dr. Edmund An- 

 drews, of Chicago, President of the Chicago Academy of Sciences, in a 

 pamphlet entitled: " The North American Lakes Considered as Chronome- 

 ters of Post Glacial Time." The portions of the raised beach lines and sea 

 cliffs in Cook county, Illinois, have been referred to by Mr. Bannister of 

 the Illinois Geological Survey, in his report on the geology of Cook county, 

 Vol. Ill, p. 2-40-2. Neither of these gentlemen have given the distribution 

 of the separate lines with sufficient detail to subserve our purpose, and slight 

 inaccuracies of distribution occur in Dr. Andrews' map which accompanies 

 his pamphlet. We, therefore, feel warranted in presenting here the distri- 

 bution and connections of the beach lines without further reference to pre- 

 vious publications, since our description is based upon those facts only 

 which we have obtained independently. 



The beach lines vary in number at different points around the head of 

 the lake, in places there being but one or two — but elsewhere, several, and 

 in Lake county, Indiana, a large number. There seem, however, to be but 

 three Imes which are maintained distinctly and vigorously for any great 

 distance. We shall describe these as the Upper, Middle and Lower raised 

 beaches. 



UPPER RAISED BEACH. 



Between Waukegan and Winnetka, Ilhnois, the lake shore is now far- 

 ther west than it was at the time of the formation of tlie upper raised beach 

 for the lake is undermining undulating tiU ridges which show no evi- 

 dence of having been submerged for any long period. North from Wau- 

 kegan raised beach lines are developed at intervals, but they have not been 

 studied ■«'ith sufficient thoroughness to warrant a description. We, there- 

 foi'e, begin our description at Winnetka, in nortliern Cook county. An an- 

 cient sea cliff passes in a southerly course from the lake bluff through the 

 eastern part of this village. The cliff is about twenty feet in height, and 

 is a prominent feature in the village. Its base is very nearly 60 feet above 

 the present level of Lake Michigan. 



Following the sea cliff south we find it soon changes to a beach line, and 

 gravel and sand in forms quite similar to those of the present beach Lines of 



