width, and has a total area of about seventy-five thousand square miles.
The central part of this plain does not resemble a mountainous country, most of it being free from any great differences of elevation. It is simply an elevated plateau. At its edges, however, the plain bears considerable resemblance to mountains, due to the action of the streams which have worn down their valleys at the edge of the plateau, leaving the land between the valleys to stand up as elevated and distinct hills or mountains. Through the central part of the plateau the fall of the streams is not very great, and consequently their action of wearing down their valleys has been slow. At the edge of the plateau, however, the slope is great, the average descent from the plateau to the Mississippi plain being about one hundred feet at the present time. Formerly it was more than this, and the streams of the plateau have carved their valleys rapidly thus making great differences of level between their beds and the untouched soil between them.
The average elevation of the Ozark plateau is about one thousand feet though there are places where the elevation is greater than this. From this central elevated part the slope extends to the northeast to the southeast and to the west.
Breaking away from this elevated dome-like region are a number of ridges extending in several directions. One of these ridges extends across the Mississippi river at Grand Tower and another at Thebes. Some other of the ridges extend to the south and cross into Arkansas, while others strike off to the southwest into Kansas and Oklahoma.
The ridge which is broken by the river at Grand Tower is called the Shawnee hills. It extends through Illinois and crosses the Ohio river into Kentucky where it gradually fades away into the other physical features of the state. It received the name Shawnee hills from the early explorers in Missouri and Illinois, who found the Shawnee Indians living along the hills. The Indians at that time were called Oshawando and this name was given at first to the hills. The point where the Mississippi river breaks through this ridge, now known as Grand Tower, is one of the most interesting places within the Mississippi valley. Even a casual examination of the spot discloses the fact that within comparatively recent times the Mississippi river flowed considerably east of its present channel. On the Illinois side above the town of Grand Tower is a great isolated rocky hill known as Fountain Bluff, which rises to a height of 635 feet above the ordinary level of the river. The channel of the river was evidently at one time to the north and east of this great bluff. One of the remarkable things connected with the formation at this place is the fact that the strata in Fountain Bluff dip are in an opposite direction from those found in the rock known as Grand Tower and the other rocks on the west side of the river. The strata are the same in general character indicating, that the formation was once continuous from Fountain Bluff to the hills on the west side, but the fact of the changed direction of the dip of the strata together with the narrowness of the channel and its precipitous sides, indicate that the break in the hills was formed by some violent upheaval.
Another of these ridges extends across the Mississippi river at Commerce, evidently having been broken here within comparatively recent times as the bed of the river is still formed of rocks and boulders, not having been worn away by the action of the
