THE TIMBER BELT OR SABINE RIVER BEDS. 31 



all highly fossiliferous. Frequently lenlicular beds of hard limestone two to 

 three inches thick and containing considerable iron pyrites occur. This de- 

 posit represents the uppermost Tertiary bed containing marine fauna found 

 by the writer on the Colorado. The overlying beds seen farther down the 

 river are treated under the head of Fayette Beds. 



The equivalents of many of the beds that have been noted on the Brazos 

 and Colorado rivers are found in many places to the northeast and southwest 

 of those regions, and a careful search will doubtless correlate them with the 

 principal strata described. In a formation of this kind, however, where most 

 al] the strata have been laid down either in coastal lagoons or in shallow bays 

 and estuaries, it must be expected to find local changes in the character of 

 the beds, dependent on the source of supply of material in the neighborhood 

 of the special deposit being formed, and also on the very variable conditions 

 which must surround the deposition of such strata. For instance, in many 

 places sandy beds occupy the same horizon that clay beds hold perhaps only 

 a few miles off. G-lauconite also varies very much in quantity in beds of the 

 same epoch, and iron pyrites, dependent as it is for its formation on the com- 

 bined decomposition of organic matter and soluble salts of iron, must from its 

 very mode of origin vary very much in quantity in different parts of the same 

 bed. The same might be said of the various other mineral constituents which 

 characterize these strata, and it is pre-eminently true of lignite beds, which 

 are the result of a certain combination of conditions so local and uncertain in 

 their scope and so liable to exist anywhere in the Tertiary series, that such 

 beds can not be relied on anywhere to determine the horizon of the enclosing 

 strata. 



Going northeast from the Brazos, along the strike of the Tertiary beds, we 

 see in Anderson, Cherokee, and Rusk counties extensive glauconitic deposits, 

 rich in Claiborne fossils. These overlie the interbedded sands and clays al- 

 ready described as occurring over the Rocky Rapids sands of the Brazos. 

 The following section, taken three miles north of Rusk, shows the relation of 

 these strata: 



1. Gray and buff sands 8 feet. 



2. Hard brown sandstone 1 to 3 inches. 



3. Brown resinous laminated hematite 1 to 3 feet. 



4. Altered fossiliferqus greensand. 30 feet. 



5. Gray clay, stained by iron in places 5 feet. 



6. Dark gray sand, with glauconite specks and rusty pyrites, giving rise 



to many ferruginous springs 20 feet. 



7.'^Gray and chocolate clays, ferruginous in places 35 feet. 



8. Interbedded seams of gray and chocolate clay and fossiliferous glau- 

 conite marl, sometimes indurated and partly altered; nodules and 

 lenses of clay ironstone 40 feet. 



