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Most of the rivers and their tributary streams crossed by the sections made, and elsewhere throughout Eastern Texas, are subject to extreme variations between high and low water marks. As a result of these extremes there are extensive areas of overflow lands everywhere along these water courses. Occasional bluffs of a height sufficient to stand above the high water mark occur close to the channel of the stream, but in places the overflows reach depths varying from a few feet to twenty-five and even thirty feet, and in some extreme instances the water has risen to forty-five feet.

The areal extent of these overflow lands cannot be given or even approximated, as they occur under all kinds of conditions and under different circumstances and vary in different years. Each main stream with its tributaries or drainage system is independent of all the others, and the width or longitudinal extent of the alluvial bottoms connected with it is governed by the conditions surrounding or forming the boundaries of the drainage area to which they belong. In many places the areas subject to overflow extend to a mile or a mile and a half in width, but throughout the greater portion of the country the width does not exceed more than a distance of three or four hundred yards.

The areas subject to these overflows are covered with a black alluvial soil. This soil is in many places thinly stratified or laminated, but in many localities shows a massive homogeneous structure. A section from the east bank of the Trinity river south of Hall's Bluff, near the confluence of Hurricane bayou and where the overflow areas are extensive, may be taken as typical of this class of deposits. The bluff formed between extreme low water and the elevation at which the overflow begins shows—

Thinly laminated dark clayey sand, with occasional deposits of dark blue clay averaging 2 inches in thickness, dipping at angles varying from 18° to 8°, gradually becoming shallower until at the top it is nearly horizontal. 14 feet