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great Atlantic Timber Belt. Westward the patches of Grand Prairie increase in area as the forests diminish, and occupy the flattened divides between the numerous streams flowing into Red River from the north. The plains of the Kiamitia (between the Kiamitia and Little River), the Goodland Prairie (between the Kiamitia and the Boggy), the Caddo Prairie (between the Boggy and the Blue), the Washita Prairie (between the Blue and the Washita), and the Marietta Prairie, west of the Washita, are the chief examples of this class.

An interesting feature of the Red River district is the fact that it is mostly of lower altitude than the prairies on the south side of the Red River fault line. This is largely because it occurs on the downthrow side of the Red River fault zone. As shown later, this feature has a most important bearing upon the artesian water question.

--In northern Grayson County there is a small disconnected body of Grand Prairie belonging to the Red River area which occurs as an inlier within the Eastern Cross Timbers and the Black Prairie. This occupies about 20 square miles to the north and northwest of Denison. Its isolated occurrence in this locality is due to the peculiar faulting elsewhere explained.

West of the Red River fault zone, between Marietta, Preston, benison, and Bells, Texas, the east-west trend of the Grand Prairie and the strike of its underlying formations which mark their occurrence in the Indian Territory change to the north-south direction which prevails in the Main Texas area, a district embracing all the belts of Grand Prairie Country between the Western and Eastern cross timbers and between Red River and the Colorado. The Missouri, Kansas and Texas Railway from Denison to Austin almost follows the eastern border of the Main Texas area. The valley of the Western Cross Timbers forms the western margin.

This portion of the Grand Prairie as a whole is a vast dip plain, which becomes more dissected and diversified to the southwest, finally passing southward into the sublevel dissected Edwards Plateau. The surface slope, with slight variations, is generally east. That portion of the Grand Prairie north of Trinity River and the eastern border in general, as far south as the Colorado, like the Indian Territory area, consists of comparatively flat and unbroken dip plains. To the west, especially south of the Trinity, the flat surfaces of the dip plains are more scarped and dissected into numerous low buttes and mesas constituting the Lampasas Cut Plain.

The prairies of the Main Texas belt are cross grooved by deeply scored valleys of numerous streamways with many branching laterals.