DEPOSITS ALONG THE MISSISSIPPI 



also to be sought, a reason why a stream should be turned from a 

 wide, deep channel, into a narrow gorge which la}^ higher than the 

 stream itself. 



At Thebes, near Cairo, is a similar gorge; for fifteen miles 

 there are bluffs along both sides of the river which is bordered 

 only by narrow strips of alluvial land, while at one place, "The 

 Grand Chain," masses of rock projecting above the surface compel 

 pilots to hold their boats in a very narrow channel. At Cape 

 Girardeau, a few miles above, the loess caps a hill fully 170 feet 

 above the level of the river bank. Here, again was an obstructed 

 ancient channel; and the question of a solid ice-dam was answered 

 in the negative at once, for the greatest southern extension of the 

 glacier was many miles above. It was deemed possible, though 

 not at all probalDle, that icebergs or floes may have found some 

 obstacle to hold them at this point until they had formed a hard 

 pack. Beginning near Cape Girardeau is a swamp fully three 

 miles in width and terminating more than fifteen miles below, 

 which was the former course of the Mississippi. Bluffs border it 

 on both sides, in most places precipices of solid limestone. As at 

 Grand Tower, no trace of glacial drift could be found above high- 

 water mark; besides, the valley of the swamp is too wide and too 

 deep for ice to have jammed. Below here, are reached the ex- 

 tensive swamps that fill the former prolongation northward of the 

 Gulf of Mexico ; and farther research was useless. 



It thus was evident that by no possibility could loess deposits 

 south of the Missouri river be due to a dam of either earth or ice; 

 and some other explanation must be worked out and investigated. 

 Wright has calculated, and brought forward proof of his 

 figures, that at its greatest diseharge during the melting of the 

 continental glacier, the Missouri reached a flood height of at least 

 two hundred feet. 



On the Illinois river, sixty miles above its mouth, are bluffs 

 of loess fully one hundred feet high, proving this stream also 

 subject to great floods. 



At the same time the Mississippi was draining a large area of 

 .ice-covered country. 



The border of the ice-sheet being in this region along a line 

 approximately east and west, these rivers would discharge their 

 immense volumes of summer water at practically the same time, 

 and not with intervals between flood height, as is now the case. 

 It is quite probable that the rise in the Mississippi, when reinforced 

 by that from the Illinois, fully equalled that in the Missouri. 

 •When all these waters united, in a channel not much wider in many 

 places than in one of the three, it follows that, either the current 

 must flow with great velocity or the water must rise to a level 

 greater below thej unction than it would naturally. Bearing upon 

 this point is an observation by Leverett, who says that "between 

 than at the present day. Yet it seems probable that at times the 



