284 



cycles of limnetic organisms at this middle reach of the river 

 comes accordingly to depend to a great extent, not upon 

 the primary contributions of the sewage, but upon secondary 

 or even later conversions of the nitrogenous matters originally 

 contributed. The decay of the vegetation of the backwaters 

 and bottom-lands, and the wastes and decay of the plankton 

 itself and of the other organisms dependent upon it, come to 

 be to a greater extent the immediate sources of support of the 

 locally developed plankton. 



COMPLETE MINERAL ANALYSES. 



Three complete mineral analyses of the water of the 

 Illinois River have been made by the Chemical Survey under 

 the direction of Professor Palmer, the samples for which were 

 collected by us at Havana. These appear in the accompany- 

 ing table. 



Analyses of Mineral Matters Contained in Samples Collected from 

 Illinois River at Havana, Illinois. Parts per Million. 



The analysis in 1897 was made in a period of prolonged 

 low water, the effect of which appears in the large amount of 

 sodium chloride, indicating the concentration of sewage, while 

 the presence of potassium nitrite suggests the active decay of 



