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The county is drained by the two rivers, the Brazos and the Navasota, and their tributaries. Along the eastern boundary Little Cedar, Big Cedar, Sandy, Bowman, Brushy (with its tributary creeks, Wickson and Mathis), Carter's, Salt Flat, and Peach creeks flow into the Navasota river. On the west the Little Brazos, Thompson, Turkey, White, and Hope creeks flow into the Brazos river. These creeks have generally wide, and most of them comparatively deep, courses or channels, but during the dry season and summer months are altogether dry, or nearly so. For the greater portion of the year water in these creeks exists only in the form of stagnant pools.

GENERAL GEOLOGY.

The geological section of Brazos county shows the alluvial or recent deposits covering many square miles bordering the Brazos and Navasota rivers, and extending for considerable distances along the channels of some of the larger creeks. These deposits range in depth from a few feet in places to 30 feet or more in the immediate vicinity of the rivers. The Quaternary gravel and sands are but sparingly represented, and only throughout the higher portions of the county In the southern portions the lower divisions of the Navasota beds appear over a small area, and consist only of gray calcareous and non-calcareous sandstones. The upper or calcareous clay division of the Navasota beds, as represented near Courtney, in Grimes county, is altogether wanting, although proof of its former presence and subsequent erosion by the combined action of the two rivers can be easily recognized. In Grimes county, along the eastern side of the Navasota river, a ridge of gray calcareous sandstones, in the form of a series of bluffs, extends from near the river about two miles west of Navasota, in a general northern direction for several miles. On the west side of the Brazos river, in Washington county, there extends a ridge corresponding in general structure and altitude, and having a course as nearly parallel to the Brazos as the Grimes county ridge to the Navasota. These two ridges both present abrupt faces riverward, and opposite each other, and by weathering are receding from both rivers. A great portion of the intervening area is now filled with recent deposits, but remnants of the eroded beds still remain in Barker's prairie, and can also be seen at the bridge across the Brazos river on the Navasota and Washington road, and at Hidalgo Falls.

Immediately underlying the beds belonging to the Navasota beds comes a series of gray sandstones, containing plant impressions in some places, and in other portions Cardita planicosta, Lam., and several gasteropods belonging to the deposits of the Claiborne age. These beds appear to mark the southern boundary of the Eocene Tertiary in this part of the State.