510 



surface and forty feet from the bank. The south-shore samples aver- 

 aged .21 parts per milHon, which, at the temperatures of the time, 

 was equivalent to 2.65 per cent, of saturation, the corresponding fig- 

 ures for the midstream samples being .267 parts per million, or 3.1 

 per cent, of saturation. The water temperatures on this date ranged 

 from 66.7° F. at 10 a. m. to yy" at 1 130 p. m. 



Midstream samples showed no increase of oxygen in the after- 

 noon, the parts per million, July 22^ being .30 at 10 a. m., .26 at 

 I 130 p. m., and .24 at 4 p. m. ; but those taken forty feet from the 

 south bank were .04, .28, and .31 for the same hours, respectively. 



The effects of sewage contamination are clearly shown by a com- 

 parison of these data with the Kankakee determinations of July 24 

 and 26, both made at 2 p. m., which stand at 9.91 parts per million 

 for the first date, and 11. 21 parts for the second — equivalent to 

 107.9 ^^^ 126.8 saturation percentages, respectively. The means of 

 the Morris determinations for afternoon hours were thus but 2.3 

 per cent, of those for the Kankakee; in other words, over 97 per 

 cent, of the oxygen normal to these waters had been removed from 

 them at this time by decomposition processes due to the amount of 

 their organic contents. 



The Bottom Sludges. — The silt and other deposits accumulating 

 on the bottom of a stream are in some respects more significant of 

 its average condition than are the waters of its current, especially 

 so as many of our fishes obtain the greater part of their food from 

 the bottom, upon which most of the plants and animals necessary to 

 their support live continuously. The current opposite Morris is so 

 rapid that the bottom is practically clean of sludge except where 

 eddies and slack-water places are especially favorable to sedimenta- 

 tion. An extensive bar of sludge from three to eight feet deep has 

 been formed in such a place between the wagon bridge and Kindle- 

 spire's landing, along the north shore of the Illinois. The upper two 

 or three feet of this deposit, except for a thin upper stratum of 

 grayish color, is a soft black ooze of homogeneous composition and 

 a strong offensive odor. It contained, from September on, immense 

 numbers of tubificid w^orms, in which respect it differed from the 

 canal deposits at Lockport, which reached at the controlling works 

 a depth, in places, of three or four feet. Plates of this sanitary- 

 canal sludge spread out in thin layers and kept for thirty-six hours 

 showed to the naked eye no signs of life. 



An extensive deposit of sludge, five or six feet deep in places, 

 has formed at the lower end of a large island half a mile above the 

 Marseilles dam, and sediments a foot or more in depth have accumu- 

 lated also in the chutes on each side of this island. In the north 



