39 [ 237 J 



me from the clay-banks of the upper part of Shayen and White rivers. It 

 is, therefore, probable that the extent of the formation due VV". is not less 

 than 250 miles by water, along which it is probably open to examination. 

 A few remarks on the physical geography of the region, which remain 

 to be made, may help to confirm this supposition. 



I shall first describe the general aspect of the country. It will be recol- 

 lected that I have represented the whole bed of clay, divided into two por- 

 tions by a band of iron stone, as having a nearly uniform thickness of 

 200 feet, and that it is intermixed with lumps of gypsum and limestone, 

 together with nodules of pyrites; so that a soil produced from such mate- 

 rials could hardly be expected to throw up anything but a meagre vege- 

 tation. It is of a character, too, to bs so acted upon by atmospheric agents, 

 as to exhibit, by the wear and tear of its superficial portions, every variety 

 of fanciful summits — domes, cupolas, towers, colonnades. &c.; imparting 

 to it a remarkably picturesque appearance, especially when contrasted with 

 the dense vegetation that borders the river, and a narrow slip of prairies 

 crowning the summits of the hills that are seen to extend themselves on 

 either side. 



The spirited pencil of Mr. GV-tlin has faithfully represented the pictorial 

 features of this country in some of the sketches contained in the first vol- 

 ume of his travels. 



The same physical causes, under other circumstances, produce new ef- 

 fects, that add to the beauty and grandeur of the scenery. Thus^ the rains 

 furrow and cut through the plastic and seleniferous clay, down to the more 

 resisting limestone ; giving rise to a sort of advancing platform, with a per- 

 pendicular elevation of from 30 to 40 feet, resembling a succession of long 

 lines of parapets. 



But I have now reached the proper place to treat of a very interesting 

 phenomenon observed in the midst of this cretaceous group. It 

 ^canoe'^^or' manifests itself by the occasional appearance of a dense smoke 

 smoking at the top of some conical hill, or along a line of country bound- 

 hills, ed by the horizon, so 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 the plastic clay, is said 

 to last at the same spot for a long time— say two or three years ; indicating 

 at them a lar^e accumulation of combustible materials. It is not, to my 

 knowledo^e, accompanied by luminous vapors, and is silently wafted along 

 the valley, which it mournfully shrouds. The observance of this phenom- 

 enon, associated with the frequent recurrence of a peculiar light and 

 spongy stone that the Missouri carries down and strews along its shores, 

 and which has been mistaken for pumice-stone, has led to the often contro- 

 verted opinion that there was a volcanic region on the upper Missouri. 

 There are, however, no true volcanoes over any portion of the United 

 Stales east of the Rocky mountains ; and it was this belief that led me to 

 the adoption of the wox^ 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 probable ori- 

 gin, I have called it a puniiciform stone, {roche pumiciforme.) 



Before proceeding to account for the appearances and circumstances at- 

 tending these smoking hills, 1 must add a few more fiicts concerning their 

 traditional and recorded history. There were none in activity when I as- 



