Lansiiw Pleistocene GeoIoQ-y. — JViiicliell. 
267 
Fig. 1. Section across the tunnel, looking north. 
special stage of erosion and inundation — some unusual storm 
and flood perhaps — and was deposited without weathering 
and remained undisturbed except on its borders." 
18. "The main excavation of the [tributary N. H. W.] 
valley probably dates back to the post Kansan erosion interval, 
and this was perhaps preceded, and perhaps determined, by a 
preglacial valley." 
19. "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." 
20. The tributary of the Missouri is narrow, steep-sided, 
steep-bottomed. It may be occupying an antecedent valley 
above its mouth but the adjustment phenomena at its mouth 
indicate that it is in a new channel fashioned by recent agen- 
cies. 
21. It is a rare case where a new channel exactly coin- 
cides with the old channel, as when for instance in the creation 
of the Missouri river by many antecedent rivers — the later 
channels would rarely be in coincidence with the earlier [say 
pre-Iowan] channels, especially at their debouchures upon the 
valley of the Missouri. 
22. The Wisconsin glacio-fluvial deposits are wanting at 
Concannon's ; and, assuming that they have been carried 
away by the Missouri, there is less reason to expect that the 
lighter and more erosible fliivio-glacial deposits of the lowan 
are preserved. 
23. The human relics are in "a. little relic-bearing deposit," 
formed by a combination of agencies. The ^lissouri river 
flowed past the site with a surface about level with the floor 
of the tunnel. In floodstage it rose twenty feet higher and 
built a floodplain as high as the ''little relic-bearing deposit" 
