fiairk] THE YELLOWSTONE PARK. 337 



Since the setting aside of the region as a national park, the 0". S. 

 Geological Survey has done much towards investigating the natural 

 phenomena found there. 40 The park is under the care of the Secretary 

 of the Interior, who is authorized to carry out the provisions of the 

 law, to make all rules and regulations tor its protection and main- 

 tenance. The superintendent is a military officer, with headquarters 

 at the Mammoth Bot Springs. 



The area of the Yellowstone Park 41 , as at present defined, is some- 

 what more than 3,300 square miles. The central portion is essentially 

 a broad volcanic plateau between 7,000 and 8,500 feet above sea level, 

 with an average elevation of 8,000 feet. Surrounding it on the south, 

 east, north, and northwest are mountain ranges with culminating 

 peaks and ridges rising from 2,000 to 4,000 feet above the general 

 level of the inclosed tableland. Beyond the mountains the country 

 falls away in all directions, the lowlands and valleys varying in alti- 

 tude from 4,000 to 0,000 feet above sea level. 



The Gallatin range incloses the park on the north and northwest. 

 It lies directly west of the Snowy range, only separated by the broad 

 valley of the Yellowstone River, It is a range of great beauty, of 

 diversified forms, and varied geological problems. Electric Peak, in 

 the extreme northwestern corner of the Park, is the culminating point 

 in the range, and affords one of the most extended views to be found 

 in this part of the country. Archean gneisses form a prominent body 

 on the west side of the range, over which occur a series of sandstones, 

 limestones, and shales of Paleozoic and Mesoxoic age, representing 

 Cambrian, Silurian, Devonian, Carboniferous, Trias, Jura, and Cre- 

 taceous strata. Immediately associated with these sedimentary beds 

 are large masses of intrusive rocks which have played an important 

 part in bringing about tin; present structural features of the range. 

 They are all of the ande-u'tic type, but show considerable range in 

 mineral composition, including pyroxene, hornblende, and hornblende- 

 mica varieties. These intrusive masses are found in narrow dykes, in 

 immense interbedded sheets forced between the different strata, and 



as laccolites. The valleys are deeply scored by ice, and the rocks of 

 the range may be found strewn all along the Gardiner River and well 



out over the valley of the Yellowstone. 



South of the Park the Tetons stand out prominently above the sur- 

 rounding count ry. the highest, grandest peaks in the northern Rocky 

 Mountains. The eastern face of this mountain mass rises with unri- 

 valed boldness for nearly 7.000 feet above Jackson Lake. Northward 

 the ridges fall away abruptly beneath the plateau lavas of the park, 

 only the outlying spurs coming within the limits of the reservation 

 For the most part the mountains are made up of coarsely crystalline 

 461 <;k lili 



