STRATIGRAPHY. 2? 



sand beds often contain considerable quantities of dark brown or gray mica. 

 The clay beds of this division vary from a pure white highly plastic clay to a 

 dark brown, or even black, material containing large quantities of lignitic 

 matter. They are generally laminated, or finely stratified, and frequently 

 occur interbedded with thin seams of sand,* the latter often in lenticular 

 streaks, while the clay is generally continuous. A very characteristic deposit 

 of this kind is seen underlying the Claiborne greensands in the iron ore re- 

 gions. The seams of clay vary from one-twentieth to one-eighth inch in 

 thickness, and the sandy seams are but very little thicker. The whole forma- 

 tion shows a peculiar undulating section, the undulations being due to the 

 thinning and thickening of the sandy seams, and not to lateral pressure.* 

 The lignite beds of this series are composed mostly of brown or black varie- 

 ties, which have not as yet been put to any important economic uses. Silici- 

 fied wood is of very frequent occurrence in these strata; sometimes occurring 

 as small fragments, and at others as large trunks of trees. 



'•Carbonate of iron,* in the form of clay ironstone, is of very frequent occur- 

 rence throughout the Timber Belt Beds. It rarely occurs in a continuous 

 seam, but is found in lenticular masses and nodules, often occupying the 

 same plane of stratification for considerable distances. Sometimes these 

 masses coalesce into a bed continuous for a few hundred yards. They are 

 rarely over three or four inches in thickness, and are generally rusty from 

 oxidation. They are probably the source of some of the brown hematite 

 ores in the counties north of the Sabine River. Iron pyrites is an almost in- 

 separable accompaniment of the Timber Belt Beds, and is also the source of 

 many of the iron ores south of the Sabine. One of the most striking ap- 

 pearances in these beds is the mottled red, yellow, and white character of 

 many of the strata. This is due to weathering, and though it is of very 

 common occurrence throughout the Tertiary, it is also seen in deposits of 

 Quaternary age." 



QUATERNARY. 



The extent of the Quaternary modifications of the underlying materials 



*"The sand seams look like a series of connected lenses blending into each other at their 

 edges. This interlamination of sand and clay was caused by the different velocity of the 

 waters that flowed over the beds during their deposition — the swifter waters carrying and 

 depositing the sand and the more sluggish waters depositing the clay It is natural that 

 such waters as would carry sand would have sufficient velocity to give a gently undulating 

 surface to the beds that they are depositing, and not the smooth level surface of a still- water 

 sediment. Thin beds of clay laid down afterwards on such a surface would naturally con- 

 form to the inequalities of the surface, and hence the undulating section that we see does 

 not require the supposition of a lateral pressure for its formation. It seems possible that 

 this same phenomenon may also account for the undulations in many of the old gneissic and 

 schistose rocks, many of which may have once been in the form of sands and clays." 



