THE TIMBER BELT OR SABINE RIVER BEDS. 39 



character from one place to another, but no decided change is seen. The 

 strata are composed of gray or buff colored sands in various degrees of in- 

 duration, from a loose material to a hard sandstone, and sometimes even to 

 a semi-quartzite, and associated with minor seams of gray or brown clay and 

 hard shelly limestone containing many fossils. Occasionally beds two to ten 

 feet thick and composed almost entirely of the shells of oysters are seen, 

 doubtless representing a littoral formation. The sands are composed largely 

 of pure siliceous grains, always containing specks of glauconite, which some- 

 times increase in number until they compose the mass of the bed. The ce- 

 menting material is usually carbonate of lime, which is here in much greater 

 quantities than in the corresponding strata to the northeast. Sometimes the 

 sands are cemented by silicic acid, and in such cases they form the hard semi- 

 quartzite rocks mentioned above. The climatic conditions in this warm, dry 

 region are such as to indurate rocks containing a cementing material much 

 more than the comparatively cool and moist climate to the northeast, and the 

 consequent greater hardness of the strata gives a much more rugged, angular, 

 and imposing topography to the country than is seen in East Texas proper. 

 The almost entire absence of timber of any kind tends still farther to enhance 

 the effect of this configuration. Springs are practically entirely absent, and 

 creeks are very rare, though their dry beds are seen in many places, and the 

 heaps of pebbles in some of them prove the great torrents that sometimes 

 come down them. They run through narrow canyons thirty to eighty feet 

 deep and with very steep sides. This form of channel is doubtless due to the 

 meteorological conditions of the region, which consist of long drouths of 

 many months at a time, .suddenly ended by spasmodic downpours. The country 

 is seen to consist of a great table land sloping gradually to the southeast, and 

 much cut up by dry creek and river beds. It is in fact the southwestern 

 continuation of the East Texas table land already described, though as it has 

 not been exposed to so much erosion as that region, it shows a greater surface 

 of the original plateau. Timber is very scarce throughout the Rio Grande 

 region, except directly on the river banks. At Eagle Pass the only vegeta- 

 tion is mesquite and cactus, with occasional areas of mesquite grass. The 

 mesquite trees are generally scrubby and low, though sometimes trunks one 

 foot in diameter are seen. On the river bluffs are also found hackberry and 

 cane. Half way between Eagle Pass and Laredo, willow becomes plentiful, 

 and increases on down to Brownsville. No large specimens are seen, as on 

 the Brazos, but it often occurs in dense scrubby thickets. Cane is plentiful 

 all along the river, and is especially dense on the water's edge, disappearing 

 a few yards back and giving place to the cactus and mesquite. This charac- 

 ter of vegetation continues to Carrizo, where we see the first cypress, forming 

 a grove just below the mouth of the Salado River, on the Mexican side. 



