Allen.] 256 [January 21, 



quent recurrence of a peculiar light and spongy stone that the Mis- 

 souri carries down and strews along its shores, and which 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 volcanos over any portion of the United States east 

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

 adoption of the word pseudo-volcano. Neither is the substance found 

 in these regions, and commonly called pumice, a true pumice ; and, 

 by a similar analogy to that which has prompted the name of its prob- 

 able origin, I have called it a purniciform stone (roche pumiciforme) ." 1 



Lewis and Clarke note the appearance of these phenomena at in- 

 tervals from their winter camp already mentioned, nearly up to the 

 mouth of the Judith River, or for a distance of not less than five 

 hundred miles. The country at the mouth of Miry Creek (Muddy 

 River of recent maps) they describe as follows : " The hills along the 

 river are broken, and present every appearance of having been burned 

 at some former period ; great quantities of pumice stone and lava, or 

 rather earth, which seems to have been boiled and then hardened by 

 exposure, being seen in many parts of these hills, where they are 

 broken and washed down into the gullies by the rain and melting 

 snow." 2 Twelve miles further on they " reached the lower point of a 

 bluff on the south, which is in some parts on fire, and throws out quan- 

 tities of smoke which has a strong sulphurous smell, the coal and other 

 appearances in the bluffs being like those described yesterday." 3 



Again at a point about forty miles above the Little Missouri they ob- 

 serve: "The appearances of the minerals continue as usual 



There is indeed reason to believe that the strata of coal in the hills 

 cause the fire and appearances which they exhibit of being burned. 

 Whenever these marks present themselves in the bluffs on the river, 

 the coal is seldom seen; and when found in the neighborhood of the 

 strata of burnt earth, the coal with the sand and the sulphurous mat- 

 ter usually accompanying it, is precisely at the same height and nearly 

 of the same thickness with those strata." 4 



At the end of the next day's journey they remark: " We had trav- 

 elled twenty-eight miles through a country similar to that of yesterday, 



1 Nicollet's Rep. on the Hydrogr. Basin of the Upper Mississippi Biyer, p. 39, 1843. 

 (Sen. Doc. 237, 26th Congress, 2d Session.) 



2 Lewis and Clarke's Exped., Yol. I, p. 180. 

 s Ibid., p. 181. 



* Ibid., p. 189. 



