52 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



waters of that river. The geologic formations are apparently entirely 

 volcanic. The bold promontory from which I made my observations is 

 formed of massive sheets of dark, coarsely crystalline l3asalt, that show 

 in the vertical faces some pretty fine columns. These basalts are ap- 

 parently associated with the conglomerates. 



The upper valley of the East Fork has but slight exposures of rock, 

 excepting in the range that encircles it, and is a beautifully diversified 

 upland, which abounds in i)arks and i)ine forests. Bands of elk were 

 met with hourly, and the forests were continually resounding with their 

 varied and somewhat extraordinary calls. 



GLACIAL PHENOMENA. 



In common with very many of the more elevated districts of the 

 Eocky Mountains, the Park district presents a variety of glacial phe- 

 nomena. In exj)loring the deep valleys of the higher ranges, the geolo- 

 gist is never surprised at encountering on all hands partially rounded 

 masses of transported rock. These are pretty sure to be found on most 

 of the old flood-planes of the streams and often high up the sides of the 

 valleys. They are frequently the only remaining records of ancient 

 glaciers which have filled the valleys at different stages of their erosion. 

 The glaciation of rocks in sitUy in the narrow gorges, also bears testi- 

 mony to the former existence of glaciers. Loose bowlders are doubtless, 

 ih many cases, carried from their original beds by the force torrents, 

 and not infrequentlv reach i)laces very far distant from their original 

 station by a gradual creeping or sliding movement — tbe result of under- 

 mining or yielding of the soil beneath. It is, therefore, far from safe 

 to conclude that wherever erratic rocks are found glaciers have for- 

 merly existed, especially in cases where these rocks may have had their 

 origin in surrounding highlands, or even quite distant mountains of very 

 considerable elevation, In a region like this, however, there is every 

 reason to suppose that glaciers once existed on a very extensive scale. 



The Park, with the great continental water-shed that surrounds it, 

 forms one of the grandest masses of highland in the United States. 

 In early Quaternary times, as now — if there have been no important 

 changes of level in the mean time — the general level of the Park district 

 exceeded 8,000 feet, and the broad areas of mountainous country on the 

 west, north, and east represent a former general elevation of 12,000 feet 

 or more. 



Glaciers exist now in the neighboring Wind Eiver and Teton Mount- 

 ains at elevations much below 12,000 feet, and in the midst of glacial 

 times descended in immense sheets to 4,000 and 5,000 feet. It would, 

 therefore, be a matter of surprise if traces of glaciers were not found 

 here, not only in the high valleys, but upon the surfaces of the broad 

 plateaus of the Park. There is, however, a singular absence of well 

 defined glacial moraines. The tens of thousands of granite bowlders 

 that occur on both sides of the Yellowstone Valley, from Cinnabar Mount- 

 ain to the north base of Amethyst Mountain, generally lie upon the 

 smooth surface of the flood planes of the river, or upon low ridges of 

 alluvial drift. The significance of this fact may be that the transport- 

 ing glaciers existed in the earlier stages of the erosion of the valley, and 

 that the morainal ridges have been destroyed by the river as it oscil- 

 lated from side to side in the succeeding stages of its descent from 

 the plateau level to its present bed. These great bowlders would, in 

 such a case, be the more durable masses of the moraines stranded on 

 the various flood planes for want of water power to transport them. 



