486 THE RIVER BLVFIS. 



tions, and melting away at last in the level prairie. Counting both banks, 

 this system of rivers alone would give a single line of elevations meandering 

 through the great plains something liife twenty thousand miles in length, 

 and rising at some points to a height above the river of five hundred feet. 



The geology of the river bluffs unfolds itself on the following dynamic 

 princij^les. In an open country like the prairies, rivers possess two elements 

 — a channel and a flood-plain. During the winter season, and some months 

 in summer, the stream is confined within the channel. But during freshets., 

 and particularly the June freshet, which is swollen by mountain snow, the 

 stream rises and spreads over the flood-plain. ISTow, should the interior of 

 the continent be elevated say a hundred feet by internal forces, the coast- 

 line remaining the same, the river would have a greater fall, quicker flow, 

 and more eroding power. A new channel and a new flood-j)lain would be 

 cut, both of less width, leaving the outer margins of the old flood-plain as 

 an elevated terrace. And the walls of the original geological suture, or outer 

 banks of the stream, would be left by the receding water to be elevated by 

 such successive epochs into river bluffs. And the partings or lips of any 

 suture in the original crust would be slightly turned up by escaping steam 

 or gases, or outward pressure of the yielding mass beneath, leaving the bluff" 

 elevated above the surrounding prairie. . Four such elevations have taken 

 place since the rivers of the eastern portion of the continent began to flow, 

 and three since the Mississippi began to pursue its course toward the Gulf. 

 As the geological elevation has been greatest toward the interior and wes- 

 tern portion of the continent, the eroding power of rivers has proportionally 

 increased, causing the river bluffs to become more prominent as physical 

 features of the country as we ascend the rivers, just, as we shall see, Avhere 

 they are needed. 



The meteorology of the river bluffs is an important element to those 

 dwelling on the great plains. People always living among hills crowned 

 with forests do not realize the force or constancy of the winds in a level 

 prairie country. At Lawrence, Kansas, for example (a place not exposed 

 as much as many points farther west), the self-registering anemometer on 

 the University building, situated on Mount Oread, furnishes the following 

 record: During the year 1875 the wind traveled 145,316 miles, which gives 

 a mean daily velocity of over 398 miles, and an hourly velocity of over 16 

 miles; These total winds, flowing uniformly over the whole j'ear, would 

 give the people of Lawrence a constant current of air between a fresh breeze 

 and a strong wind. On January 8, 1875, at the same place, the wind attained 

 a velocity of seventy-fiye miles an hour, a violent gale, only one remove 

 from a hurricane. 



The same general belts of wind, running east and west, prevailed around 

 the globe. But the forest-crowned hills of j^few England and the Middle 

 States drive these currents up into the higher regions of the atmosphere. 

 NoAvthe river bluffs are the natural wind-breaks of the great central jDlains, 

 and Avithout them the prairies would be a bleak, an almost uninhabitable 

 plateau. 



