80 CHICAGO ACADEMY OF SCIENCES. 



print and copies of it are difficult to obtain, the computations made 

 by Dr. Andrews are presented below. Dr. Andrews apparently 

 includes the beachlets referred to above in the present lake stage. 



The lake is encroaching upon the district on its west border 

 from the Wisconsin line southward to Chicago, though piers 

 built along the shore in Chicago and for some distance north- 

 ward now prevent further encroachment. Along the border 

 of Hyde Park, in the south part of Chicago, the lake is 

 building a beach and is tending to fill ifi rather than to extend the 

 lake in that region. In Indiana the lake is filling in rather than 

 extending its borders. In Southwestern Michigan it is eroding the 

 prominent parts and filling in the bights, thus giving the lake a 

 more regular outline. In this connection it may be remarked that 

 the effect of the lake generally is to remove the prominent parts 

 and fill the bights. 



Dr. Andrews computed the bulk of the beach as follows : For 

 25 miles west from Michigan City it maintains an average cross 

 section of about 6,000 square yards, and its 'contents are 264,- 

 000,000 cubic yards. In this division the beach is in the form of a 

 lofty belt of sand dunes, about one-third of a mile wide, and in 

 places 160 to 200 feet in height. In the next eight miles west this 

 beach spreads out into a broad belt of low parallel ridges, about 

 two miles in extreme width. This division has a cross section of 

 about 16,000 square yards, after deducting the sand which was 

 deposited by Lake Chicago. Its contents amount to 225,280,000 

 cubic yards. From the Indiana line, near Wolf Lake, to Chicago 

 River, a distance of sixteen, miles, the sand occupies a belt esti- 

 mated to be seven yards thick on the shore and running out to a 

 thin edge at the average distance of 2,500 yards inland. It, there- 

 fore, has a cross section of 8,750 square yards and contains 246,- 

 400.000 cubic yards. To this should be added the portion of the 

 beach under water. This, taken for the entire distance from Chi- 

 cago to Michigan City, is estimated to be about 1,011,890,000 cubic 

 yards. The computation of the subaqueous belt is as follows : The 

 sand at the shore line is about 10 feet deep, and it extends out to 

 where the water reaches a depth of 24 to 36 feet. The breadth 

 varies greatly, ranging from about 1,000 yards to nearly five miles, 

 the v;idest part being at the head of the lake. The total bulk of the 

 lake deposits, both in and out of water, in the section between 

 Michigan City and the mouth of Chicago River, is estimated to be 

 1,747,570,000 cubic yards. 



