32 GULF TERTIARY OF TEXAS. 



9. Gray clay, with seams of sand, and some clay ironstone 5 feet. 



10. Interstratified gray and chocolate clay 5 feet. 



11. Lignite 1 foot. 



12. Chocolate clay 1 to H feet. 



12. Lignite. 1 foot. 



14. Chocolate clay 6 feet. 



15. Interbedded chocolate clay and small seams of lignite, i to -| inch 



thick, at base of section. 



The greensand bed near the top of the section is probably the representa- 

 tive of the Smithville bed on the Colorado. It is composed of glauconitic 

 grains, with more or less green clay, the latter often occurring in the form of 

 interbedded seams or lenticular patches. The bed is generally rusted on the 

 surface, from the combined decomposition of the glauconite and the iron pyr- 

 ites that it contains, but the interior preserves its green color. The fossils 

 are generally in the form of casts, but in some places the shells are well pre- 

 served, and sometimes, though rarely, oblong and kidney-shaped calcareous 

 nodules one-half to three inches in diameter are found. The bed is of very even 

 thickness, varying over very large areas from thirty to forty feet. This deposit 

 underlies a large part of northern Anderson and Cherokee counties, and forms 

 the dividing ridge between the Angelina River and the Neches, and between 

 the Neches and the Trinity, besides occupying the summit of some of the other 

 highest points in East Texas. 



The underlying sands and clays are the equivalents of the beds overlying 

 the Rocky Rapids sands on the Brazos, and also of those below Bastrop on 

 the Colorado. As there, they consist of interbedded and interlaminated sands 

 and clays, often cross-bedded, stained by decomposed iron pyrites, and con- 

 taining numerous small beds of lignite. These strata are extensively devel- 

 oped all over Cherokee and Anderson counties, and thence on up to the Sa- 

 bine River, wherever the overlying greensand has been eroded. The sands 

 are frequently indurated by a ferruginous or siliceous cement into beds of 

 sandstone, varying very much in hardness, color, and thickness. The beds 

 with a ferruginous cement vary from yellow to very dark brown in color, and 

 have been solidified by the percolation of water containing soluble salts of iron. 

 The beds with a siliceous cement have been solidified by similar waters con- 

 taining silicic acid or soluble silicates, and are of a white or buff color. Such 

 beds vary from one to twenty feet thick, and are of very limited extent. They 

 generally cap knolls and hills, and form a protecting cover which saves the 

 underlying strata from erosion. (See Building Stones.) The glauconitic de- 

 posit itself finally dips under the overlying clays and sands to the southeast, 

 and gives place to the lignite-bearing region of northern Angelina and other 

 counties. 



Some two hundred feet below the iron-bearing greensand bed is a similar 



