CHAPTER IV. 



DESCRIPTIVE GEOLOGY OF THE NORTHERN END OF THE 



TETON RANGE. 



By Joseph Paxson Iddings and Walter Harvey Weed. 



INTRODUCTION. 



The Teton Range is the highest and most imposing of the mountain 

 ranges that environ the Yellowstone Park. The three highest peaks, whose 

 spire-like summits and perpetual snow fields are visible from every outlook 

 of the Park, form a well-known feature of Wyoming scenery, giving the 

 mountains the familiar name of the Three Tetons. Only the northern spurs 

 and lesser peaks of this range occur within the region surveyed — that is, 

 north of the forty-fourth parallel of latitude. This northern part presents 

 none of the impressive features of height and scenery that occur in the 

 main portion of the range farther south, yet geologically this limited area 

 is of great interest, since it includes the northern end of the Archean nucleus 

 of the range, with the flexed and upturned sedimentary rocks encircling it. 

 The great epochs of geological time are all represented in the stratigraphic 

 section exposed in these northern peaks, while the relations of the eroded 

 range to the accumulations of basic volcanic breccias and to the great 

 rhyolite flows of the Park Plateau are here revealed. 



The area shown on the map (PL XNIII) includes an accidented region 

 that is the divide between the waters of Falls River Basin and those of the 

 valley of the Snake. The two most prominent streams, Owl Creek and 

 Berry Creek, cut deeply into the uplifted rocks, exposing Archean gneisses 

 and the overlying Paleozoic strata. Two prominent summits, known 

 as Survey Peak and Forellen Peak, rise above the general level of the 

 rhyolite plateau. The region is well wooded, but is diversified by parks 

 and grassy valleys that add to its attractiveness. The recently built road 



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