224 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



miles, its shore line approaches 100 miles in length ; a fact whose biological signifi- 

 cance will be understood if we call to mind that the greater part of the food of 

 fishes in such a lake is to be found among the weeds of its shoal waters alongshore. 

 From a main body (a fairly regular parallelogram, 7 by 12 miles) several large arms or 

 bays project to the west and south, giving the whole lake an extreme length of 20 

 miles and a width of 14. The immediate banks are generally abrupt, although not 

 high, with a narrow gravel beach, and except along the tributary streams, there is 

 little or no swampy ground tibout the shore. The Yellowstone above the lake, how- 

 ever, runs, as do most streams in this region, through a wide, swampy bottom, which 

 must afford an immense field for the breeding of fishes and for the growth of their food ; 

 and Pelican Creek, the next largest tributary, is similarly situated, while several of the 

 smaller creeks have each at their mouth a little bar, piled up by waves and ice, which 

 has partly stopped the outlet and so formed above it a weedy lagoon or marshy bay. 



The bottom commonly slopes gradually downward, making an abrupt descent, so 

 far as known, only from the shores of Frank Island and from the lofty summits about 

 Southeast Bay. Beyond the beach of gravel and boulders which commonly borders 

 the lake, comes usually a belt of sand or sandy gravel, and beyond this a sandy mud, 

 becoming finer and darker inwards, until in the deepest water reached it was a very fine 

 black ooze. The greatest depth reported by the Hayden survey was 300 feet, in the 

 center of West Bay. My owu deepest soundings were incidental to our dredging oper- 

 ations, and were limited to a distance of 2,000 feet from shore off our camp at Hot 

 Spring Basin on West Bay, and to an area north and east of Stevenson Island, where 

 the lead was dropped at distances varying from half a mile to 2 miles from the island. 

 The greatest depth reached in this area was 231 feet, at a point nearly equidistant 

 from Stevenson Island and Steamboat Point. 



My only temperature observations were made August 4, 1890, at which time the 

 suiface temperature of the water was 62 F., the bottom at 100 feet was 46, and at 

 184 feet, 42. 



This lake lies almost at the summit of the Bocky Mountain watershed, the con- 

 tinental divide following approximately the outline of its western and southern borders 

 for about 40 miles, at distances varying from a mile to 5 miles from the shore. To the 

 westward of the lake lie broken pine-covered hills, which rise from 250 to 800 feet 

 above its level. To the north are the dark ridge of the Elephant's Back, about 850 feet 

 above the lake, and the Sulphur Hills, which finally rise to a height of 9,000 feet above 

 the sea. On the east lies a mass of rugged volcanic mountains, a part of the Absaroka 

 Range, patched with snow all summer. They approach the shore most closely along 

 the southeast arm at the upper end, where the scenery is very bold and fine. A few 

 peaks rise to a height of 11,000 feet above the sea at a distance of 5 or 6 miles from 

 the shore. The boldest elevations are those just below the mouth of the inlet, where 

 mountains less than 2 miles away reach a height of 9,600 feet. 



Besides the Upper Yellowstone and Pelican Creek, already mentioned, the principal 

 tributaries to the lake are a number of small streams which drain these eastern moun- 

 tains, and, taking their waters from the melting snows and flowing most of their way 

 through overhanging forests, bring to the lake a considerable amount of very cold 

 water. The hot springs and geysers are found mostly on the western arm and at 

 Steamboat Point in the northeastern part of the lake, but the amount of warm water 

 contributed by them is quite insignificant for so large a lake. 



