1874.] 255 [Allen. 



same river. 1 I find also that I have noted this vicinity as the highest 

 point at which we met with these beds in our last season's exploration 

 of the Yellowstone. Thence to its mouth they occur with more or 

 less frequency, often forming the most striking features of the country 

 for long distances.' 2 



Leaving the Yellowstone and proceeding eastward to the Missouri, 

 between the parallels of 46° and 47°, these reddened beds only occur 

 as the capping of isolated and often widely separated buttes, till one 

 approaches the Bad Lands of the Little Missouri. Crossing this belt 

 of igneous action, already sufficiently described, the traces of this 

 metamorphism suddenly almost wholly cease, but occur still eastward, 

 at widely separated localities, to within about one hundred miles of 

 the Missouri. To the eastward of the Little Missouri Bad Lands, 

 however, these brick-like materials form but a thin capping to a few 

 low mounds, where the scattered fragments of the reddened clay-chips 

 resemble not a little the debris covering the sites of abandoned brick- 

 yards. Mixed with the brick-like materials are fragments of scoria 

 and pumiceous matter, while pieces of pumice stone are occasionally 

 met with thence eastward to the Missouri, and I gathered speci- 

 mens at Fort Eice so light as to float in water. 



Fragments of pumice stone have been found on the Missouri as far 

 south as the vicinity of Fort Pierre, and by the early explorers were 

 supposed to be the products of unknown volcanos situated near the 

 Rocky Mountains. Lewis and Clarke first met with "pumice stone" 

 near their winter quarters on the Missouri, about fifty miles above the 

 mouth of Heart River, to which they refer as follows: " Captain 

 Clarke passed along the points of the high hills, where he saw large 

 quantities of pumice stone on the foot, sides and tops of the hills, 

 which had every appearance of having been at some point on fire." 3 

 Mr. I. N. Nicollet, in his exploration of the Upper Mississippi in 1839, 

 ascended the Missouri as far as Fort Pierre, where he appears to have 

 heard of these appearances of metamorphism and of the " smoking 

 hills"; but he seems not to have actually seen them himself. Allud- 

 ing to the smoke that had been seen to issue from some of these hills, 

 he says : " The observance of this phenomenon, associated with the fre- 



1 Hayden's Geol. Rep. Expl. Yellowstone and Missouri, p. 103. 



2 As high up as the mouth of the Rosebud, the pebbles in the bed of the Yellow- 

 stone consist largely of scoriaceous matter and indurated shales, brought down 

 doubtless by its eastern tributaries, probably the Tongue and Rosebud Rivers. 



3 Lewis and Clarke's Expedition, (American Ed.), Vol. i, p. 173. 



