American Fisheries Society 187 



may be here mentioned, although it grew out of our aquatic 

 work outside the Ilhnois basin. One large section of the 

 State of Illinois, comprising about a fifth of its area, is 

 peculiar in the absence, or at least in the unusual rarity there, 

 of a considerable group of fishes which are abundant else- 

 where in the state and elsewhere in the surrounding terri- 

 tory. Now this section, the conditions of which these fishes 

 evidently do not tolerate, is distinguished from the re- 

 mainder of the state by its geological history, and, as a 

 consequence, by the different character of its soil and of 

 its streams. The soil is so finely divided that its particles 

 cannot be wholly separated from the water, even by re- 

 peated filtering with the finest filter papers, and it thus 

 remains persistently and perpetually turbid. The fishes 

 which seem to avoid this situation are, on the whole, those 

 which we find in other parts of the state to be relatively 

 infrequent in very muddy water. The inference is plain 

 that it is the permanently muddy character of these south- 

 ern Illinois streams, itself due to the geological history of 

 the district, which renders them unfit for these more sensi- 

 tive fishes. Any attempt, consequently, to increase the 

 number of such fishes there would be foredoomed to fail- 

 ure. Doubtless there are many other instances of the same 

 sort to be found in other parts of the country, and it seems 

 possible that various mysterious failures of attempts made 

 to introduce new fishes are attributable to some such cause, 

 not taken into account because unknown. 



We have now a long waiting list of special practical in- 

 quiries which seem clamoring to be made. We need, for 

 example, to observe most carefully the European carp, now 

 undergoing enormous multiplication in our interior waters; 

 to learn the details and the variations of its food and its 

 habit under different conditions ; to study the bearings and 

 consequences of its spread and increase on the welfare of 

 our native fishes, and on the whole system of fresh-water 

 life; to watch for evidences of local overpopulation by it, 

 to be suspected when the carp or its competing species fall 



