527 



From a comparison of the first column of this table, showing the 

 collections taken from the shallow water near the mouth of the 

 Fox, with the other columns, it is plain that Fox River water was 

 greatly preferred by fishes at this place, and it seems likely indeed, 

 that most of the specimens taken at this point had come into the 

 river from the Fox itself. The common shiner is, as usual, a nota- 

 ble exception, this abundant lake and river minnow being unusually 

 tolerant of polluted waters. 



Starved Rock 



The odor of the water at Stan^ed Rock, August, 191 1, was still dis- 

 agreeable, but there were no bubbles of gas from the bottom, and there 

 was sensibly less suspended matter in the water than at Marseilles. 

 North of the island the stream was perceptibly cleaner and of a 

 greener color than in the south channel, probably because it carried 

 a larger admixture of Fox River water, with its greener plankton. 

 The surface temperature of the water was 78° F. August 15, and 

 72° August 26. The effect of Fox River contributions to the Illinois 

 was plainly manifest by an average difference of 21 per cent, between 

 the oxygen ratios of the two sides of the Illinois, as shown by 

 seventeen sets of tests made August 15 and 26, 191 1, and February 

 23, August 22, September 6 and 28, and October 11 and 26, 1912. 

 The lowest ratio of the series was 2.5 parts per million from the 

 south shore, September 6, 191 2, and the highest was 5 parts per 

 million, also from the south shore, October 26. The general aver- 

 age for the south shore was 3.23 parts per millon (35.9 per cent, of 

 saturation), and that for the north shore, with its larger admixture 

 of Fox River water, was 3.91 parts per million (43.6 per cent, of 

 saturation). 



The only sewage organisms found were isolated filaments or mi- 

 nute tufts of Sphcrrotiliis natans floating in the current. Minnows, 

 identified as golden shiners and spot-tailed minnows (Notropis hud- 

 sonius) were seen swimming near the surface on both sides of the 

 river. This is the first observation of the second of tliese species. 

 An old resident of the town informed us that a considerable variety 

 of fishes is to be found here, practically at all times, but that the 

 numbers are never large. 



In 19 1 2, collections were made at Starved Rock September 3 and 

 9 and October 9 to 11. The water had still a slight sewage odor, 

 but less than at Ottawa. SphccrotUus and Carchesiuiii were occa- 

 sionallv seen attached to weeds and grass at the edge, and moderate 



