770 T. C. CHAMBERLIN 



of history probably arose the variations in color, texture and 

 effervescence in response to acid, which were observed. The 

 material of the one distinctly water-laid layer was probably 

 derived from the Carboniferous shales at some special stage of 

 erosion and inundation — some unusual storm and flood, perhaps 

 — and was deposited without weathering, and remained undis- 

 turbed except on its borders. 



2. The truncated faces of the adjacent Missouri bluffs, and 

 the numerous slides on these faces, show that the Missouri river 

 has worked extensively and effectively across the mouth of the 

 tributary only a few rods from the site of the relics, and that this 

 has been comparatively recent. 



The rather steep slopes of the tributary valley favor the view 

 that the present fashio?iing of these is recent. The main excava- 

 tion of the valley probably dates back to the post-Kansan 

 erosion interval, and this was perhaps preceded, and perhaps 

 determined, by a preglacial valley. But the valley, as it is ?iow 

 fashioned, is pretty closely adjusted to the Missouri river bottoms 

 which are features of recent origin, and this adjustment a?id the 

 slopes and deposits involved in it is, by rather strong presumption, 

 to be connected with the development of the adjacent Missouri 

 channel. The age of the original valley and of the upland 

 mantles does not concern us here, unless these lower deposits, 

 well down in the axis of the valley, and at its junction with the 

 great river bottoms, are surely inheritances from the older period, 

 and not adjustment phenomena. 



3. The record of these earlier events is here very imperfect. 

 Even the record of the more recent of the Pleistocene events is 

 very scant where it should be abundant and decisive if the con- 

 ditions of preservation had been favorable. In Dakota, where 

 the Missouri river came into relation with the last stages of gen- 

 eral glaciation within its basin, there are three great systems of 

 terraces as worked out by Todd, T viz. : 1 ) "The higher bowldery 

 terraces," varying from 500 feet to 350 feet above the Missouri 

 and connected with the outer moraine of the Wisconsin stage ; 

 2) "The lower bowldery terraces," varying from 350 feet to 



1 Todd, Bull. U. S. Geol. Surv., No. 158, pp 128-154. 



