200 



The Origin and Accunnihtthm of tlic Sdnd. — Estimates were made 

 several years ago by Dr. Andrews tt> determine tlie amonnt of sand be- 

 longing to the Lake Chicago deiwsits and the amount belonging to the worli 

 of the present lake. It was found that the lake was encroaching upon 

 the western liorder and on the eastern border along southwestern Michi- 

 gan. In Indiana the lake is filling in rather than extending its Iwrders. 

 The estimates sh(jw that the comliined bulk of the beaches formed by Lake 

 Chicago is nearly eipial to that due to the present lake. The length of 

 time involved in tlie accunmlation of the beach deposits was estimated by 

 measuring the amount of s.-mkI carried southward past the piers at Chi- 

 cago and Michigan City. The sand stopped by the two piers annually 

 was found to be 121>.(HlO cubic yards. Since the estimate shows that not 

 more than one-1'oiirth or one-tifth of the drifting sand is stopped by the 

 piers, the i>eri<Kl for the accunudation is given as less than (j,00<) years, 

 or about 3,000 for Lake Michigan. Dr. Andrews has also estimated the 

 age of the lake from the annual amount of destruction from the bluffs. 



"Dr. Andrews's estimates were based on the assumption that there 

 is a southward-flowing current on each side of the lake, carrying sand 

 to its present head. Investigations made liy the Weather Bureau in 1892 

 and 1893, under the direction of Pro. Mark Harrington, led him to the 

 conclusion that the currents on the east shore in the southern portion of 

 the basin are northward instead of southward. He accounts for the ac- 

 cumulation of Siind on the north side of breakwaters along this coast by 

 the action of the surf, in storms blowing from the north which is more 

 transient than the currents proper and would affect the southern part of 

 Lake Michigan only when the wnid was in tlie north. This occasional 

 phenomenon is very ellicii'nt when it occurs. He concludes that the esti- 

 mates of the time involved in the formation of l»eaches have less value 

 than they w(»uld have if the accunudatioiis were due more largely to 

 lake currents. 



"Considerable study of th(> movement of water in Lake Michigan has 

 been made by the Chicago Drainage Commission, largely under the direc- 

 tion of Professor Cooley. As a result of these investigations, which in- 

 volve not only a study of bottle papers but also a thorough canvass of the 

 opinions of lake captains and an examination of breakwaters, Cooley has 

 reached the conclusion that the effective work on the shores is due to 

 waves and not to currents, and it is a matter of doubt if this lake has 



