THE DISTRIBUTION OF SPECIES. 



205 



miles long and two hundred wide. For days they passed 

 in clouds that darkened the earth with the gloomy hue of 

 an eclipse, while the ground was covered with crawling 

 millions, devouring every green thing, and giving to the 

 country the appearance of being carpeted with scales. 

 It has been discovered, however, that before they attain 

 their winged state they can easily be destroyed, and en- 

 ergetic measures will be taken against them throughout 

 all the inhabited districts of Australia whenever they 

 make another appearance." (Station Life in Australia, 

 Scribner's Magazine, February, 1892, pp. 136-154.) 



I was lately called to examine a specially interesting 

 problem in geographical distribution, that of the disper- 

 sion of fishes in the Yellowstone Park. 

 Trout in Yellow- Thig ion . ^ h yolcanic plateau 



stone Park. 



formed by the filling of a mountain basin 



with a vast deposit of lava. The streams of the park are 

 for the most part among the coldest and clearest of the 

 Rocky Mountains, and apparently in every way suitable 

 for the growth of trout. All the hot springs of the great 

 geyser basin are not sufficient to warm the waters of 

 the Firehole River. Yet, with the exception of the Yel- 

 lowstone itself, all these streams are destitute of fish life. 

 A reason for this is apparent in the fact that the plateau 

 is fringed with cataracts which no fish can ascend. Each 

 stream has a canon and waterfall near the point where 

 it exchanges the hard bed of lava for the rock below. 

 So the best of trout streams, for an area of fifteen hun- 

 dred square miles, are left without trout, because their 

 natural inhabitants can not get to them.* 



* Since this was written, the principal waters of this region 

 have been stocked with trout of different species, and these have 

 multiplied with great rapidity. There is now an abundance of 

 trout in the Firehole, Gibbon, Gardiner, and Lewis Rivers, as well 

 as in Shoshone Lake. 



