12 GULF TERTIARY OF TEXAS. 



the Gulf, but the transition is gradual, and it is impossible at any place to 

 draw a sharp division that might represent the " falls line," or line of separa- 

 tion of the highland and lowland. These rivers rise in various parts of the 

 State, and hence the sediments which the comparatively swift waters of their 

 upper courses carry down and deposit in the quieter basins in East Texas 

 vary considerably in character. The Red, Brazos, and Colorado rivers rise 

 in the eastern slopes of the Staked Plains, in Northern Texas, pass through 

 the Red (gypsiferous) Beds, the Paleozoic rocks, and the great Cretaceous 

 area of Central Texas, and finally deposit in East Texas a sediment composed 

 of materials from these regions, in the form of a highly calcareous red silt. 

 The Trinity rises in the Carboniferous rocks of Northern Texas, but far east 

 of the Staked Plains, and passing down through the Cretaceous prairies, be- 

 comes charged with calcareous matter. Hence its sediments, though often 

 calcareous, do not have the red color of the Red, Brazos, and Colorado riv- 

 ers. The Sabine rises still east of the Trinity, while the smaller rivers, such 

 as the Neches and Angelina, rise in the timber region, and the character of 

 the sediments of them all varies with the region they rise in and flow through. 



Though terraces of gravel and river silt are found along the rivers, and 

 sometimes reach down to the water edge, yet all of them may be said to flow 

 in channels cut in the older sediments, as such strata crop out at very frequent 

 intervals along their courses. In this respect they resemble the Mississippi, 

 in connection with which a similar statement has been made by Humphreys 

 and Abbot*. 



Loughridgef gives the following drainage areas for some of the East Texas 

 rivers : 



The Sabine River, on the Texas side, drains 17,100 square miles. 



The Trinity River drains ..... 16,600 square miles. 



The Brazos River drains 35,000 square miles. 



The Brazos has a greater drainage area than any other Texas river. It re- 

 ceives many tributaries in its upper part, but below the basin is narrow, and 

 small streams instead of emptying into it run. direct to the Gulf. All of the 

 Texas rivers are navigable to a greater or less extent, and until the introduction 

 of railroads an extensive shipping business was carried on in transporting the 

 cotton production of the region. Of course the amount of freight that could 

 be carried depended on the high or low condition of the water. Now, how- 

 ever, boats rarely go up them for any considerable distance, as the journey 



*" Report on the Physics and Hydraulics of the Mississippi River," by Captain A. A. 

 Humphreys and Lieutenant H. L. Abbot, 1861. 



f R. H. Loughridge's " Report on the Cotton Production of the State of Texas, with a Dis- 

 cussion of the General Agricultural Features of the State." Tenth Census of the United 

 States, Vol. V, 4884, pp. 653-831. 



