513 



inorganic materials of the silt. As there is no reason to suppose that 

 the river was carrying a larger load of mineral substances at Henry 

 than at Marseilles, the differences of the table are probably due in 

 part to a settling out, and in part to a decomposition of organic con- 

 taminations before the river water reached the Henry dam.* 



Marginal Conditions, July, igii. — The septic conditions above 

 described were general at Morris for the stream as a whole, but were 

 considerably modified along the margin in very shallow water, es- 

 pecially in pockets protected against the current. Water an inch deep 

 near the north bank contained 3.5 parts per million of oxygen in the 

 forenoon of August 31 and 6.1 parts in the afternoon, (38.9 per 

 cent, and 69 per cent, of saturation,) while midstream samples gave 

 1.05 and 1. 1 8 parts per million at the same hours (11.4 per cent, 

 and 13.3 per cent, of saturation). The green-thread alga, Stigeo- 

 clonimn tenue, formed many patches on the bottom even in July, in 

 water four to six inches deep; and the oxygenation of the marginal 

 water was largely the work of these plants. Here also were very 

 many tubificid and naiid worms (Tubifex and Dero furcata), together 

 with aquatic insects {Notonccta, Ncpa, and Gyrinidcc, and a few 

 Chironomus larvae); but there were no clams (Unionidce) or snails 

 or crawfishes or larvse of May-flies or of dragon-flies. 



Plants and Animals of the Stream in general, July, igii. — Gen- 

 erally speaking, the plants and animals of this part of the river in 

 July, 191 1, were either conspicuous by their absence, if clean-water 

 forms, or by their excessive abundance, if pollutional or contaminate 

 species. Sphcurotilus imtans, for example, was hanging to every 

 stick or grass-blade along the edge, and to every suspended particle, 

 small or large, and was attached everywhere to the stems of branch- 

 ing Vorticellidce, especially to Carchesinm lachmanni. Specks or 

 larger collections of these two latter most abundant foul-water forms 

 were so numerous, indeed, as to give the water a grayish look. There 

 was every indication that these characteristic sewage organisms were 

 coming at this time mainly from the Des Plaines above the mouth 

 of the canal, and not directly from the sanitary canal itself, in which, 

 in fact, they were not then abundant. The microscopic population 

 of the large, soft masses floating down stream at Morris in July was 

 mainly made up of a great variety of fungi, alg?e. Protozoa, and 

 rotifers, of which the most abundant were Sphcurotilus natans, Os- 

 cillatoria limosa, Colpidiuni colpoda, Carchesium lachmanni, and Roti- 

 fer actinurus. 



No fishes were seen or heard of here in the Illinois durmg this 



*For additional data concerning the sludges in the winter time, and for all 

 sections of the river, see p. 552. 



