200 



The Origin and Accumuldiion fit flic tSand. — Estimates were made 

 several years ago by Dr. Andrews t<> determine the amount of sand be- 

 longing to the Lake Chicago deposits and the amount belonging to the work 

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

 the western border and on the eastern lioi-dcr along southwestern Michi- 

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

 The estimates show that the combined bulk of the beaches formed by Lake 

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

 time involved in the accunudation of the beach deposits was estimated by 

 measuring the amount of sand carried southward past the piers at Chi- 

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

 was found to be 129.(KJ0 cubic yards. Since the estimate shows that not 

 more than one-fourth or one-fifth of the drifting sand is stopped by the 

 piers, the period for the accumulation is given as less than 6,000 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 by 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 sand 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 wuid was in the north. This occasional 

 plieiiomeno;i Is very eliicicut whiMi it occurs. lie roiu Indcs that the esti- 

 mates of the time involved in the formation of beaches have less value 

 than they would liave if the accumulations were due moi'e largely to 

 lake curi'ents. 



"Considerable study of the movement of water in Lalce Michigan lias 

 iteen made by the Chicago Drainage Conunission, largely luider the direc- 

 tion of Trofi'ssor Coolcy. .\s a result of these investigations, which in- 

 volve n(jt only a study of bottle i>apers but also a thorough canvass of the 

 opinions ol' lake cai)tains and an examination of iireakwater.s, Cooley lias 

 leachcd the conchisioii tlint the (■ITccti\(' work on the shores is due to 

 waves and not to currents, and it is a iiiallci- of doulit if tliis lake has 



