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Iron Ore Knobs.
The Iron Ore Knobs of Grayson County extend east and west from Alchire switch, 7 miles west of Denison, to Red River. These knobs as seen between Sherman and Denison consist of low, rough, sandy hills densely clad with black-jack and post oak.
From the summit of the Iron Ore Knobs an exactly similar and parallel row of hills-the Caddo Knobs-can be seen some 30 miles northward, across the valley of Red River, in southern Indian Territory. This row of knobs, which is the interior margin of an extensive prairie dip plain sloping toward Red River, extends from the Washita River a few miles south of old Fort Washita eastward for 15 miles to the Missouri, Kansas and Texas Railway, beyond which it has not been explored.
Both of these parallel east-west belts are ultimately occupied by the valley of Red River, which intercepts that of the Iron Ore Knobs at the northwest corner of Fannin County and that of the Caddo Hills some distance eastward, in Lamar County. Where so followed by the rivers the cross timbers and the formations upon which they grow are so associated with the undergrowth and recent and old alluvial soils that it would be impossible to map them until minute studies are made.
Economic Features.
The Eastern Cross Timbers are admirably adapted to fruit growing, and the strata upon which they are established are of great importance to the question of artesian water. To appreciate the water conditions of this region it is necessary for the reader to know the sequence of the great rock sheets of the Black Prairie and the Eastern Cross Timbers, their water-bearing and water-transmitting capacity and their topographic lay, as given in subsequent pages.
THE GRAND PRAIRIE SUBPROVINCE.
General Character and Relations.
The Grand Prairie includes the portion of the East-Central Province situated west of the Eastern Cross Timbers in Indian Territory and Texas. It has an area of about 20,000 square miles and presents within itself many diverse features.
Although often confounded with the Black Prairie, the Grand Prairie differs from it in many minor physical features. In general the surfaces are flat rather than undulating, and the valley slopes are angular (scarped or terraced) rather than rounded. The residual soils and regolith are shallow in comparison with those of the Black Prairie belts, and are of chocolate or brown colors instead of black, although in at least one belt (the Del Rio) the latter color prevails. Owing to