THE ANCIENT MlSSlSSlFPl AND ITS TRIBUTARIES. 617 



sents the Valley of the Mississippi losing one foot off its whole surface, "in 6000 

 years. And were this to continue without any elevation of the land, the Conti- 

 nent would all be buried beneath the sea in a period of about four and a half 

 million years. But, though this wasting is going on, the Continent will not dis- 

 appear, for the relative positions of the land and water are constantly changing, 

 in some cases the land is undergoing elevation, in others, subsidence. Prof. 

 Hilgard has succeeded in measuring known changes of level, in the lower Mis- 

 sissippi Valley, and records the Continent as having been at least 450 feet higher 

 than at present, (and if we take the coast survey soundings, it seems as if we 

 rm'ight substitute 3000 feet as the elevation), and subsequently at more than 450 

 -feet lower, and then the change back to the present elevation. 



Let us now study the history of the great river in the last days of the Coeno- 

 zoic Time, and early days of the fifth and last great Geological Time, in which 

 we are now living — the Quatenary, or Age of Man — an epoch which I have 

 called the " Great River Age." 



It is to the condition of the Mississippi during this period and its subsequent 

 changes to its present form that I wish particularly to call your attention. During 

 the Great River Age, we know that the eastern coast of the Continent stood at 

 least 1200 feet higher than at present. The region of the Lower Mississippi was 

 also many hundred feet higher above the sea level than now. Although we have 

 not the figures for knowing the exact elevation of the Upper Mississippi, yet we 

 have the data for knowing that it was very much higher than at the present day. 

 - The Lower Mississippi, from the Gulf to the mouth of the Ohio River, was of 

 enormous size, flowing through a valley with an average width of about fifty miles, 

 though varying from about twenty five to seventy miles. 



In magnitude, we can have some idea, when we observe the size of the 

 lower three or four hundred miles of the Amazon River, which has a width of 

 about fifty miles. But its depth was great, for the waters not only filled a channel 

 now buried to a depth of from three to five hundred feet, but stood' at an eleva- 

 tion much higher than the broad bottom lands which now constitute those fertile 

 alluvial flats of the Mississippi Valley, so liable to be overflowed. 



From the western side, our great river received three principal tributaries — 

 the Red River of the south, the Washita, and the Arkansas, each flowing in 

 valleys from two to ten miles in width, but now represented only by the depau- 

 perated streams meandering from side to side, over the flat bottom lands, generally 

 bounded by bluffs. 



The Mississippi from the east received no important tributaries south of the 

 Ohio ; such rivers as the Yazoo being purely modern and wandering about in the 

 ancient filled-up valley as does the modern Mississippi itself. 



So far we find that the Mississippi below the mouth of the Ohio differed from 

 the modern river in its enormous magnitude and direct course. 



From the mouth of the Ohio to that of the Minnesota River, at Fort Snelling, 

 the characteristics of the Mississippi Valley differ entirely from those of the lower 

 sections. It generally varies from two to ten miles in width, and is bounded 



