204 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



thousand or two thousand feet higher. The plateau is glaciated, and ponds 

 and lakes diversify the surface, which is almost completely destitute of soil 

 or vegetation. Along the southern flanks of this crystalline axis the over- 

 lying Paleozoic strata dip away from the central mass of Archean rocks. 



The area embraced within the limits of the Yellowstone Park, although 

 but a small part of the range itself, includes a part of the Archean massif. 

 The schists and gneisses are deeply trenched by streams flowing southward 

 from the mountains and joining the Yellowstone drainage within the Park. 

 Only scattered remnants of the Paleozoic rocks which formerly covered 

 the crystalline schists are now found. To the south very greatly eroded 

 sedimentary masses are now covered by the volcanic breccias. 



TOPOGRAPHY. 



The topography of that portion of the Snowy Mountains included 

 within the mapped area presents a variety of configuration, due primarily 

 to the nature of the rock masses. For the purposes of the present dis- 

 cussion the southern limit of the range may be regarded as defined by the 

 Yellowstone River, its eastern fork, Lamar River, and the eastern branch 

 of the latter stream, known as Soda Butte Creek. Within the triangular area 

 thus inclosed we have, to the south, the sharp volcanic summits of Druid and 

 Bison peaks and the long, narrow crest of Baronet Peak. To the north and 

 west broad, gently sloping summits extend southward and break abruptly 

 in steep slopes and limestone cliffs to the valleys of the streams that drain 

 the region. The principal drainage of this area is that of Slough Creek 

 and its tributary, Buffalo Creek. The former stream, heading in the glacial 

 amphitheaters of the rugged peak known as Haystack Mountain, flows in a 

 southwesterly direction through a wide and generally open valley whose sides 

 expose excellent sections of the mountain-forming rocks. The topographic 

 peculiarities of the stream indicate that it is of considerable antiquity. The 

 present valley bottom is deeply filled with alluvium, apparently the result 

 of the damming' of the stream in glacial times and the formation of a lake 

 above the narrow canyon which it has cut through Archean gneisses to join 

 Buffalo Creek. The latter stream has, within the limits of the area mapped, 

 cut a valley in Archean gneisses, the gently dipping sedimentary beds 

 which occur upon the flat plateau summits on either side being far above 

 its present channel. 



