35 [ 237 ] 



prairie, laid down upon my map. This would have been, at the time, a 

 subject of ^reat regret to me, had I not been informed that, in continuing 

 to ascend the Missouri, I was to meet a series of bluffs of the same char- 

 acter. Accordingly, a third bluff soon presents itself on the right side of 

 the river, and three miles south of the trading-post which was occupied by 

 a Mr. William Dixon. 



Before entering upon a description of this bluff, I would remark that, 

 T,. . ^, ^. as the rocks of which it is composed are the same that con- 

 stantly make their appearance on ascending the river, at the 

 base of the hills that bound the valley. 1 shall content myself with de- 

 scribing them once for all. Moreover, to facilitate the reference which it 

 may be necessary to make to the different geological divisions of a group 

 of rocks which 1 propose to consider under the name of Dixon's group, 

 or Dixon's bluff, (so called by me, after the trader that lived near the 

 spot, and v/ho has been one of iny most devoted guides during my ex- 

 plorations over the great prairies situated more northerly,) 1 shall note tlie 

 divisions of this group, in their ascending order, by the letters of the alpha- 

 bet, viz: 



A. Argillaceous limestone, containing inoceranms bambini, in great num- 

 ber and very much compressed, and so arranged as to give the rock a slaty 

 structure. This stratum sinks below the bed of the river, and consequently 

 its thickness is indeterminable ;. that part of it above the water on the day 

 of my examination was three feet. Starting from this place, and ascend- 

 ing the river, this rock must necessarily disappear below the level of the 

 water. It is probably more conspicuous in the two preceding cliffs I have 

 referred to before, but which I had not an opportunity of examining. The 

 upper portions of the rock that I did examine contain nodules of iron 

 pyrites, being an assemblage of small cubic, cubo octaedral, and octaedral 

 crystals. 



B. A calcareous marl, generally from 30 to 40 feet thick, but at this spot 

 reduced, by a slide, to 15 or 20 feet. Its colors are gray, grayish-blue, and 

 sometimes yellow. It contains but very few fossils. I found, myself, but 

 one orbicula, and what appears to be a tish scale. 



C. This is a slightly ferruginous clay bank of a yellowish color, with 

 seams of selenite, and affording occasionally rounded masses somewhat re- 

 .sembling septaricB. The selenite is in acicular crystals, or in its more 

 usual form of rhombic prisms x'^ariously truncated. 



Such are the three divisions that I have thought necessary to make in 

 this group of rocks, and which are always thus associated as the river is 

 ascended. This group is the basis of the cretaceous formation of the Mis- 

 souri. The upper subdivisions, which I shall have occasion to establish 

 further up, and that are not sufficiently distinct here, will complete an ac- 

 count of this interesting formation. It may not be impertinent to remark 

 in this place, that it is most likely the bluffs between the Sioux and Ayoway 

 rivers, a distance of only twelve miles, are, geologically, similarly consti- 

 tuted as Dixon's bluff; the cretaceous formation rests here on the carbonif- 

 erous or mountain limestone. 



On quitting Huppan-kuley prairie, the entrance to the Wassisha, or 

 Riviere Vermillion river, and that of the riviere Jacques of the French, 

 Jacques, the Tc^an 5a«5an of the Sioux, are passed by in succession. la 

 this interval, the valley hills are at a distance, and the cretaceous forisu- 

 ation is not easily followed up; but, a little further on, it reappears oa 



