"396 KEACTION OF THE INTERIOR OF THE EARTH 



River (Clarke's Fork), it becomes more regular and 

 simple. Clarke's Fork and Lewis (or Snake) Eiver 

 form the great Columbia Eiver, which will one day be 

 -an important commercial route. (Explorations for a 

 railroad from the Mississippi River to the Pacific Ocean 

 made in 1853-1854, vol. i. p. 107.) 



As is the case in Bolivia, where the eastern chain of 

 the Andes, in which are the mountains of Sorata (21,288 

 feet) and Illimani (21,148 feet), does not now present 

 any still active volcanoes, so also in these western parts 

 of the United States volcanic activity is at present 

 limited to the coast chain of California and Oregon. 

 The long chain of the Rocky Mountains, of which the 

 distance from the sea coast of the Pacific varies from 

 480 to 800 geographical miles, and having no traces of 

 still-subsisting volcanic activity presents, however, like 

 the eastern chain of Bolivia in the valley of Yucay ( 542 ), 

 on both its declivities volcanic rocks, extinguished 

 craters, and even lavas with included obsidian and fields 

 of scoriae. In this part of the Rocky Mountains, which 

 has been described from the excellent examinations of 

 Fremont, Emory, Abbot, Wislizenus, Dana, and Jules 

 Marcou, the last-named distinguished geologist enume- 

 rates three groups of ancient volcanic rocks on the two 

 declivities. The earliest proofs of the volcanicity of this 

 district were also due to Fremont's observational habits, 

 commencing in 1842 and 1843. (Report of the Ex- 

 ploring Expedition to the Rocky Mountains in 1842, 

 and to Oregon and North California in 1843 1844, 

 pp. 164, 184187, and 193.) 



On the eastern slope of the Rocky Mountains, on the 

 south-western route from Bent's Fort on the Arkansas 



