ish congenial homes for sunfishes, bass, and even several species of dart- 

 ers. That these are not there must be due to the nature of the lower 

 courses of the streams draining the hills, and that of the Cheyenne, to 

 which they are all tributary. The Cheyenne is ordinarily a shallow 

 stream whose waters are always more or less alkaline and filled with solid 

 matter in suspension from the extremely easily eroded country through 

 which it flows. The lower courses of the streams flowing from the Hills 

 are through the same Cretaceous beds and partake of the same character. 

 Only those species with which the struggle has become most severe will 

 be driven to seek protection and food in the muddy, alkaline streams, and 

 they alone would eventually find their way into the purer, clearer waters 

 above. This, of course, means the soft-rayed, non-rapacious lishes, the 

 suckers and minnows and other mud-loving forms. 



The spiny-rayed species are aggressive, extending their attacks to all 

 weaker forms about them, while the soft rayed species are defensive, and 

 seek protection in retreat. A spiny rayed fish has no occasion to ascend 

 into the muddy, alkaline and uncongenial portions of these streams ; the 

 only thing which would cause him to do so would be a quest for foo 1, but 

 he finds it easier and more agreeable to get food of sufficient quantity and 

 quality where he is. Not so with the soft-rayed fish ; he must not only 

 search for suitable food, but he must also see that his enemy, the spiny- 

 rayed fish, does not catch him. The attacks of his enemies were proba- 

 bly the first cause impelling him to take refuge in the turbid water. Find- 

 ing suitable and sufficient food in this new environment, and total relief 

 from the persecutions of his old enemies, he finds the struggle for exist- 

 ence easy, the surroundings in time become bearable and perhaps agree- 

 able, he moves about at will through all parts of the muddy stream and 

 even into the headwaters where, still finding an abundant food supply 

 and none of his old enemies, he is content to make his home. 



Before mining began in the Hills in 1875 and 1870, nearly every stream 

 possessed all the natural conditions necessary to make it an excellent 

 trout stream. The waters were clear and cold, not subject to contamina- 

 tion from any gource, and suitable food, such as insects and insect larva. 

 and the smaller Crustacea and mollusca, was undoubtedly found then, as 

 now, in abundance. With the exception of a few streams which are now 

 ruined by mining operations, the creeks of this region are yet excellent 

 lor trout. 



The explanation for their absence is practically the same as that which 



