CHAPTER II 



DETAILED STUDY OF THE SEDIMENTARY DEPOSITS OF THE 



LAKE CHICAGO BASIN 



I. General Statement 



A careful study in great detail was made of the north shore channel during 

 its construction, upwards of 63 distinct section stations being established. 

 A larger number of intermediate check examinations were also made. These 

 sections cover a distance of over eight miles, and pierce, for the most part, the 

 bed of an ancient bay of Lake Chicago, known as Wilmette Bay. These studies 

 have Heen supplemented by investigations in other parts of the region, in the 

 aggregate covering a large part of the old bed of glacial Lake Chicago. 



Measurement s are in inches. Each section is divided into numbered strata, 

 the stratum of each section being, for the most part, correlated in number 

 with the same level of the other sections. The biological remains of each stra- 

 tum are tabulated for all sections where evidences of life were found. 



II. The North Shore Channel (Plate II) 

 The north shore channel of the Chicago drainage system extends about eight 

 miles north of Foster Avenue, Bowmanville, uniting with Lake Michigan be- 

 tween North Evanston and Wilmette, just north of Gross Point. The channel 

 is cut in the bed of a long bay which formed a part of glacial Lake Chicago. 

 The sedimentary strata, — sand, gravel, and clay — rest on the till of the Late 

 Wisconsin ice sheet. Between Foster Avenue and Devon Avenue, the ground 

 moraine is undulating in cross section (see Plate III), differing strikingly from 

 the region north of Devon Avenue, where the deposits rest upon a till plain 

 which is comparatively level. This undulating ground moraine extends 

 southward well toward the center of the city of Chicago. The greatest diver- 

 sity of sedimentary deposits is found from Devon Avenue southward. A full 

 discussion of the limits of the flooded area will be found in Chapter III. 



In the present chapter the different sections are taken up in detail, beginning 

 with the strata south of Foster Avenue and continuing northward to Lake 

 Michigan. Sections from other parts of the city are also considered and com- 

 pared with those of the north shore channel. Each station section is located 

 its distance in feet from a well-known street, and its height above sea level 

 (A.T.) and above Lake Michigan (A.L.M.) is given. The sedimentary strata 

 are numbered from the boulder clay to the surface and the character of the 

 deposit, as well as its thickness, is indicated in inches. The level of Lake 

 Michigan is placed at approximately 580 feet above sea level (579.63 feet, 

 vide map of Sanitary Commission of Chicago). 



