PHYSICAL GEOGRAPHY. 11 



as to awaken the idea of distant volcanoes ; hence I have 

 chosen to call them pseudo-volcanoes 



" The smoke from these hills and the crevices in tlie 

 plastic clay is said to last at the same spot for a long time — 

 say two or three years ; indicating at them a large accumu- 

 lation of combustible materials. It is not, to my knowledge, 

 accompanied by luminous vapors, and is silently waited 

 along die valley which it mournfully shrouds. The observ- 

 ance of this phenomenon, associated with the frequent 

 recurrence of a peculiar light and spongy stone that the 

 Missouri carries down and strews along its shores, and 

 whicli has been mistaken for pumice-stone, has led to the 

 often-controverted opinion that there was a volcanic region 

 on the Upper Missouri. There are, however, no true volca- 

 noes over any portion of the United States east of the 

 Rocky Mountains ; and it was this belief that led me to the 

 adoption of tlie word j)seudo-volca?2o. Neither is the sub- 

 stance found in tlicse regions, and commonly called pumice, 

 a true pumice ; and, by a similar analogy to that which has 

 prompted tlic name of its probable origin, I have called it a 

 pumiciform stone {roche pumiciforme). 



" Before proceeding to account for the appearances and 

 circumstances attending these smoking hills, I must add a 

 few more facts concerning their traditional and recorded 

 history. There were none in activity when I ascended the 

 Missouri in lb39 ; and so would seem to have been the case 

 at the passage of Lewis and Clark at the beginning of tliis 

 century. But, previous to my arrival, since the memoral)le 

 expedition last referred to, and during a period of three 

 years, they were seen, as my information goes, by many in- 

 telligent persons engaged in the fur-trade, all of wliom are 

 naturally observant, and most of them of umpicsliunabK^ 

 authority. I liave no doul)t, tlierefore, of the existence of 



