ormous. It was brought down doubtless in large part by the great rivers which occupied the present position of the Mississippi and Ohio, perhaps at one time much larger than the present streams.
The soil now found in the alluvial section is not, however, the original deposits. There seems good reason for believing that the clay ridge known as Crowley's ridge is a remnant of the original deposit in the valley. This first deposit was raised up by the action of the forces beneath the surface and was then sculptured down by the action of the stream. This action has been going on for many thousands of years doubtless and the original deposits have been removed in large part except Crowley's ridge. Not only has the river sculptured the original deposits, it seems to have meandered back and forth across this great valley now washing the bluffs along the eastern side and now those along the western side, alternately sculpturing away deposits of alluvium and reforming them in other places.
The alluvial plains as they now exist then represent two separate cycles of stream action. The first consisted in filling in the arm of the Gulf of Mexico with alluvial deposits. This was separated from the second cycle of the stream action by the uplift of the deposited material above their former level; in the second cycle they are wearing down and redistributing this uplifted material into its present position. There seems no reason to doubt that within a comparatively short geologic time Crowley's ridge will entirely disappear under the action of the forces now at work upon it.
It is evident that there exists a complete contrast in physical characteristics between these two sections of Southeast Missouri. The most obvious of these differences is the fact that there are no hills in the alluvial section, while the whole Ozark uplift is dotted with them. There is also a marked difference in the streams; those of the plateau having their origin in springs of clear limpid water, flow between banks which are sometimes steep and even rugged in appearance. They have a swift current, are narrow and deep, but such of them like Castor, Whitewater, and the St. Francois which pass from the uplift to the alluvial plains undergo a complete change of character. They are no longer deep, narrow, and swift of current, with well marked banks, but they become wide and shallow and spread out over many miles.
The soils, too, are different. In the upland are the clays. They follow the outline of the hills on which they were deposited. The characteristic soil of the plains is a sandy loam, while gravels, clays and marl are to be found in places. The distinct characteristic soil is that which makes the great ridges on which are situated the flourishing towns of the district.
In minerals, also, the contrast between the sections is striking. No other section of equal size in the world contains a greater variety and wealth of minerals than the Ozark plateau. Here are to be found the great deposits of copper, zinc, lead, iron, and others. The alluvial plains on the other hand have no minerals except bog ore. The materials of which the plains are formed are the loose elastics. While the plains are lacking in mineral wealth, they possess great supplies of timber. The hills are covered in many places with timber, but the valuable trees in greatest numbers are to be found in the rich soil of the low lands. Here flourish the cotton wood, oak, gum, cypress, and hickory in great