GEOLOGICAL SURVEY OF THE TEREITORIES. 



45 



Butte, which was described last year. (Fig. 6.) I will, however, call to 

 miud here the remark in the preceding chapter ia regard to the outcroj)- 

 ping of limestones of Carboniferous age in most unexpected places. 

 On the east side of the East Fork the granite rocks seem to have pre- 

 vailed. On the summits were some trachytes or couglomerates, but be- 

 fore reaching the forks of the East Fork, the high mountains are com- 

 posed mostly of the conglomerate, while at the very base, the limestones 

 crop out 50 to 100 feet thick. Soda Butte is located about the midd^" 

 of the valley, 

 and is an ex- 

 tinct gevser. 

 (Fig. 70 'The 

 materials of the 

 m o u n d a r e 

 mostly calcare- 

 ous, and show 

 clearly that 

 these lime- 

 stones run un- 

 der the valley, 

 and that the 

 waters of the 

 geysers arose to 

 the surface 

 through them, 

 dissolving more 

 or less lime in 

 the passage up- 

 ward. 



As we ascend 

 this valley, we 

 soon tind our- 

 selves hemmed 

 in on either side 

 by walls of vol- 

 cimic breccia 

 2,000 to 3,000 

 feet in height. 

 The upper por- 

 tions have been 

 weathered into 

 the most re- 

 markable and 

 attractive pyra- 

 midal and cas- 

 tellated forms. 

 Indeed, all 



these volcanic conglomerates have a tendency to waste away into very 

 artistic architectural forms. On the east side of the valley there is an 

 irregular terrace-area covered mostly with quaking-aspens and pines, 

 formed by land-slides. On this terrace, which is elevated about 250 feet 

 above the river, there are a number of small lakes, fed by the melting of 

 the snows from the mouutain-sides. One of them is about one-fourth of 

 a mile long, and is full of trout varying in length from 10 to 15 inches. 

 We might here ask the q-uestion how these little lakes, so far above the 



