LAKES AND TARNS. 19 



the same function in the regimen of the streams at their sources. The grassy turf 

 on the uplands and around the margins of the lakelets and tarns, and the tangle of 

 willows and heavy sward which spreads over the swampy and marshy tracts have 

 the same beneficent influence and action on the water conservation in these alpine 

 areas that the forest cover has on the regions at middle elevations. The grass cover 

 effectually prevents gullying and excessive evaporation. If the grass is destroyed 

 gullying begins, the loosened material silts the hollows and depressions that hold the 

 lakelets, the water level is raised without corresponding elevation of the natural 

 embankments at their outlets, and finally the lakelets are levelled and drained. In 

 order that the grass cover of these tracts may remain intact and serve the important 

 purpose it now does, grazing will have to be closely watched and. regulated. Sheep- 

 ing, whether in large or small bands, should be entirely prohibited, and the number 

 of cattle and horses allowed on the tracts should be restricted to the lowest possible 

 number. On the lands included in Beartooth Plateau and situated within the 

 area discussed, gullying is apparent as yet only in isolated localities and has not 

 proceeded to any alarming extent. But on the lands of the plateau across the 

 Wyoming line and in the region surrounding Beartooth Lake, the evil effects of 

 overgrazing, as displayed in the formation of gullies, are abundantly in evidence. 

 Great gullies are opening out in the slopes of the ridges hemming in this lake on 

 the west, the gullying following exactly the lines of excessive sheeping. On this 

 particular tract a large band of cattle was pastured during the summer of 1903. 

 They were rather closely herded, and to escape flies and other insect pests were 

 accustomed to bunch up on comparatively small tracts near the lake. Where this 

 bunching occurred, as well as on adjacent areas which were being overgrazed in 

 consequence, the turf was quite as completelj' destroyed as ever it was on bedding 

 places of sheep, showing that there are no essential differences in the effects 

 following overgrazing, whether accomplished by cattle or sheep. 



liAKBS AND TARNS. 



Bodies of standing water, other than marshes and swamps, cover 32,500 acres 

 of the reserve. Without exception thev owe their existence to past glacial action. 

 Some occupy shallow basins and glacial cirques in the alpine areas, dammed and 

 held back by ledges of rock, or by walls of morainic debris across their outlets. 

 Others are situated in the bottoms of canj^ons and are formed and held back by the 

 remains of terminal moraines stretching across the valley. Most of them are 

 shallow and of small area. The largest in the reserve is Mystic Lake in T. Y S., 

 R. 16 E., covering 1,500 acres, situated in the canyon of West Kosebud Creek. 

 The lakelets are most numerous in the southern ]3ortions of the reserve, in the 

 high, extensively glaciated alpine areas east of upper Stillwater River, where they 

 are found by the hundreds, occupying shallow depressions in the great granite uplift 



