426 



SCIENCE. 



[N. S. Vol. IX. No. 221. 



field seems even yet scarcely explored. I 

 pi'efer, therefore, to place before you some 

 results of personal observation in a region 

 in which I have worked for several years 

 and in which I have become deeply inter- 

 ested. 



The Absaroka Range lies along the east 

 side of the Yellowstone Park. Several of 

 its higher peaks and its long western spurs, 

 sloping gradually toward the Park, lie 

 within the national reservation. During 

 several successive summers, while engaged 

 in geological observations in the Park, I 

 found it necessary to penetrate beyond its 

 boundaries into the higher encircling moun- 

 tains. My first excursion into the Absa- 

 rokas was undertaken in the summer of 

 1885, and thereafter for several years I made 

 long and protracted journeys into this rug- 

 ged and at that time almost unknown re- 

 gion, studying its geology, and returning 

 each year more and more profoundly im- 

 pressed by its many marvels. In the year 

 1893, and again in 1897, the greater part of 

 the summer was occupied in exploration of 

 the wild recesses of the Absarokas. 



The range, which lies wholly in the State 

 of Wyoming, stretches from the Beartooth 

 and Snowy ranges, on the north, southward 

 to the Owl Mountains. In width it is less 

 sharply defined, certain outlying plateau- 

 like areas, such as Mirror and Two-Ocean 

 plateaus, being separated from the main 

 body by deep valleys. Geographically they 

 may be considered as distinct physical fea- 

 tures. Geologically, from their mode of oc- 

 currence and the nature of the rocks, they 

 are intimately associated with the central 

 mass, and for the purposes of this address 

 they may be considered as forming a part 

 of the Absaroka Eange. As thus defined, 

 the range measures SO miles in length by 

 50 miles in width, covering an area of nearly 

 4,000 square miles. 



From one end to the other the Absarokas 

 present a high, imposing plateau, with ele- 



vations ranging from 10,000 to over 12,000 

 feet above sea level. This entire mass is 

 made up almost exclusively of Tertiary 

 igneous rocks. N"ear the northern flanks 

 Archean schists and gneisses crop out from 

 beneath the overlying rocks. Eesting upon 

 the Archean, upturned Paleozoic limestones 

 and sandstones having a considerable thick- 

 ness come to the surface, and along the 

 eastern borders of the range, exposed by 

 erosion in the broader valleys, occur Cre- 

 taceous rocks. With these exceptions, the 

 range consists of a vast accumulation of ag- 

 glomerates, tuffs, lava flows and intrusive 

 masses. 



Degradation of the mass has taken place 

 on a grand scale. Vast quantities of vol- 

 canic ejectamenta have been removed from 

 the summit, but no reliable data exist by 

 which the amount can be estimated even 

 approximately. All the higher portions 

 have been sculptured by glacial ice. Enor- 

 mous amphitheatres have been carved out 

 of the loose agglomerates, and peaks, pin- 

 nacles, and relics of great tablelands testify 

 in some measure to the forces of erosion. 

 The plateau is scored by a complete network 

 of deep valleys and gorges, which dissect it 

 in every direction and lay bare the structure 

 of the vast volcanic pile. 



Nowhere in the northern Eocky Moun- 

 tains do I know grander and more rugged 

 scenery than can be found in the Absarokas. 

 But few natural passes lead across the 

 mountainous tract, and these are high and 

 difficult to scale. For years the range stood 

 as an impassable barrier to the earlier ex- 

 plorers in their attempts to reach the sources 

 of the Yellowstone from the east ; and even 

 to-day the region is seldom penetrated to its 

 inmost recesses except by those engaged in 

 scientific exploration of the country, by the 

 prospector in search of precious metals, or 

 by a few adventurous sportsmen in pursuit 

 of the big game of the Eockies. Much of 

 this region is covered by a dense growth of 



