28 



SCIENCE. 



[YOL. YI., No. 127. 



and the St. Lawrence River. The site of the 

 cit}" was once covered twenty feet or more by 

 the waters of Lake Michigan, whose western 

 rim, at no very remote period of geologic time, 

 was some eight or nine miles west of its pres- 

 ent position with reference to the cit}' of Chi- 

 cago. The recession of the lake resulted in 

 the formation of a series of sand-dunes or 

 ridges, with intervening ponds and lagoons, 

 which graduall3^ filled up with the humus of 

 peat-producing vegetation. This formation 

 was the original site of the city, with an average 

 elevation of only twelve feet above the lake, 

 and much of it being so low as to be subject 

 to overflow, even by the ordinary variation of 

 the lake under the influence of north and north- 

 east winds. ^ Through this low, flat, swampy 

 plain there eventually cut its way to the lake a 

 narrow, sluggish stream, the present Chicago 

 River. Forking about a mile and a half from 

 its present mouth, its north branch runs in a 

 direction generall}' parallel with the lake shore 

 for a distance of some twenty miles ; while its 

 south branch, after running due south for about 

 two miles, tends sharply to the south-west for 

 a mile or more, and then divides into two 

 smaller branches, the western one of which is 

 separated from the Des Plaines River by a nar- 

 row ' divide ' of only a few feet elevation. In 

 seasons of high water, this ' divide ' was for- 

 merly obliterated by the flow of the Des Plaines 

 into Lake Michigan, and for several 3'ears an 

 artificial communication has existed between 

 these two streams through the so-called ' Og- 

 den ditch.' In 1848 the Illinois and Michigan 

 canal was completed, connecting this south 

 branch of the Chicago River with the Illinois 

 River at La Salle, ninety-six miles south-west ; 

 and in 1871 the summit-level of the canal, 

 twentj'-six miles long, had been lowered from 

 twelve feet above, to eight feet and a half be- 

 low, the ordinary level of Lake Michigan : so 

 that, theoreticall}', the Chicago River now rises 

 in Lake Michigan, and empties into the Missis- 

 sippi through the Illinois and Michigan canal 

 and the Illinois River. The primary object of 

 the construction of this canal was purely com- 

 mercial, but it has since become one of the 

 most important factors in the sanitary welfare 

 of the city. 



As the cholera epidemic of 1849-50 led di- 

 rectl}^ to the introduction of lake-water, and the 



1 The highest point above the level of Lake Michigan, for 

 fifteen miles north, is only thirty-eight feet; and south-east for 

 the same distance, only twenty-three feet. Directly south of the 

 city, the surface is almost level, the highest point within sixteen 

 miles heing only twenty-two feet. Southwest for ten miles the 

 highest point is only ten feet, where, at the Summit, the waters 

 of the St. Lawrence run north-east, and those of the Mississippi 

 south-west. From the Summit tliere is a gradual descent, until 

 tlie ground is lower than the surface of the lake. 



foundation of what is, in some respects, now 

 the most magnificent S3^stem of water-supply 

 in the world, so the repeated epidemics of chol- 

 era and dysentery led to the adoption, in 1856, 

 of a system of sewerage, which, within twenty- 

 four years thereafter, had furnished more linear 

 feet of sewers per capita of population than 

 in any other of the large cities of the Union. 

 For fourteen j-ears (1843-56 inclusive^) the 

 average annual death-rate of the city had been 

 37.91 per thousand, probably the highest of any 

 city in the United States ; during the first fif- 

 teen 3^ears of sewer-construction (1856-70), 

 the average annual death-rate was reduced to 

 23.97 per thousand ; while, from 1871 to 1884 

 inclusive, the average has still further fallen to 

 21.40 per thousand. And although there have 

 been marked fluctuations from j-ear to j^ear, 

 — rising to 32.22 in 1866, and falling to 16.49 

 in 1878, — on the whole, there is, as I have 

 shown in a table published elsewhere,^ a strik- 

 ing correlation between the annual death-rate 

 and the number of feet of sewers per capita 

 year by year, independent of all other influ- 

 ences. 



But while the sewerage of the Gviy has been 

 one of the most important agencies in this re- 

 duction of the death-rate, it has necessaril}^ 

 added to the pollution of the river and its 

 branches, and from time to time has affected 

 the purity of the water-supply. To such pro- 

 portions did this evil speedily attain, that in 

 July, 1860, — onl}^ four 3^ears after the system 

 was adopted, — the sewerage commissioners 

 recommended that the canal be deepened and 

 enlarged, so as to create a constant current 

 from the lake into the Illinois River, as a meas- 

 ure indispensable to the protection of the 

 health of the city. The recommendation was 

 not heeded at the time ; and for some years 

 thereafter, Mr. Chesbrough, the sewerage engi- 

 neer, continued to urge, as a practical measure 

 of temporary relief, the construction of covered 

 canals or aqueducts from the lake, with appa- 

 ratus for forcing lake-water through them into 

 the north and south branches respectively, and 

 so to create a current from the river into the 

 lake, pending the construction of a system of 

 intercepting sewers or the deepening of the 

 canal, — both of which measures he had ably 

 discussed from time to time, from the year 

 1855. 



Meanwhile the volume of sewage and of oflfal 

 from the slaughter-houses and other sources, 

 pouring into the river, continued to increase 

 with alarming rapidity ; and although the foul- 



1 Certificates of causes of death were first required in 1841, 

 but records were not begun until June 1, 1851. 



2 « The sanitary problems of Chicago, past and present.' 



