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These prairies change the topography, and incidentally the soil and native growth, and occur almost altogether within the area underlaid by the rocks belonging to the Navasota group. The most important are Wallace prairie in the southeastern, Grimes, Navasota, and Fuqua prairies in the central and western, Roan prairie in the northeastern, and Anderson prairie in the northwestern portions of the county.

GENERAL GEOLOGY.

The geological section shows broad stretches of alluvial or river deposits extending along the rivers and larger creeks throughout the county. The Quaternary deposits are almost exclusively confined to the southeastern portion, where they exist in the form of a yellowish-gray sand, intermixed with and overlaid by a coarse gravel. Thin scattering deposits of this gravel also occur at various places in the northern portion of the county.

Underlying these deposits are a series of beds of calcareous clays and sands and calcareous sandstones, which, for stratigraphic purposes, have for the present been denominated the Navasota beds. They rest unconformably upon a series of gray sandstones and quartzites, associated with extensive deposits of lignitic sands, clays, and small deposits of lignite.

The general dip of all the beds is in accordance with that of the Tertiary and later deposits of Southeast Texas. The course is south 30 degrees east. The dip of the lowermost, or Eocene, division is approximately 50 feet per mile, while the Navasota beds do not exceed 25 to 30 feet at the base, with a general shallowing or decreasing dip toward the upper portion of these deposits.

The general section shows approximately the thickness of the several deposits to be: