236 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



FLATHEAD RIVER SYSTEM. 



The waters of the Fhithead region from which collections were made by us were 

 Swan and Plathead lakes and Flathead, Swan, and Coiur d'Alene rivers, and the 

 Jocko at Kavalli. Those from the lakes only can be here discussed. 



Flathead Lake. Although this lake stands in some respects in decided contrast to 

 Yellowstone Lake, these differences tend largely to neutralize each other. Flathead 

 Lake is over 200 miles farther northward than Yellowstone, but the latter is 4,775 feet 

 the higher above the level of the sea. These lakes lie on opposite continental slopes, 

 their waters passing respectively into the G-ulf of Mexico and the Pacific Oceau, but 

 neither is more than a few miles from the relatively low continental divide, easily 

 passable by most of the plant and animal forms likely to occur in such waters. Both 

 lakes lie in the course of streams of considerable size, but these streams flow iu 

 opposite directions, the inlet of Flathead Lake coming southward from the British 

 Possessions, and its outlet running first to the south and then to the west as Flathead 

 Kiver, a branch of the Columbia, while Yellowstone River, rising about 50 miles 

 above the lake, runs northward more than a degree below it before swinging to the 

 east to join the Missouri. Nevertheless, the headwaters of the two river systems inter- 

 lace almost inextricably through interlocking mountain valleys along several hundred 

 miles of the main Kocky Mountain range. Both lakes lie among mountains from 

 whose rugged gulches the snow never wholly disappears, and both are bordered by 

 forests broken by park-like openings on the lower slopes; but the geological structure 

 of the surrounding country and the chemical composition of the rocks which form 

 their shores and beds differ widely for the two, and the forests, all pine and fir and 

 other conifers around Yellowstone Lake, are largely deciduous trees about Flathead. 



The lakes are similar in size and are both deep enough to give a deep-water 

 character to their interior fauna, but Flathead has much the more uniform shore-line 

 and contains if I may judge from the parts of it which we examined a larger 

 extent of shallow and weedy water. It is divided, iu fact, by a chain of islands 

 stretching across its lower third, into unlike parts ; the northern deep and clear, and the 

 southern shallow, and easily stirred up to its clayey bottom by the winds. 



Finally, both lakes, like most of this region, are evidently far smaller now than 

 they were in an earlier geological period. The extension of the old Flathead above 

 the present lake is shown by the terraces marking its former shores, which may be 

 traced, one above the other, for a considerable distance above the inlet; while Hayden 

 Valley, the deserted part of the Yellowstone Lake, lies below the lake along its pres- 

 ent outlet. 



The Flathead is reported by steamboat men and residents to be about 25 miles 

 long by 10 or 12 wide, although the best published map of the region makes it 24 

 miles long by 17 wide; but as the country about has not yet been surveyed, neither 

 distances nor proportions are precisely known. 



The immediate surroundings of this lake are attractive in the extreme. Beside it 

 on the east lies the Mission Kange of mountains, beginning to rise almost from the water's 

 edge, and presenting to a near viesv, along the lower half of the shore, a curiously reg- 



