BASAL OR WILLS POINT CLAYS. 19 



It is, however, too early to theorize on this subject, as the data are as yet 

 very few and scattered. The great stretch of country between the Brazos and 

 the Sabine will doubtless clear up many mysteries. 



BASAL OR WILLS POINT CLAYS. 



At the base of the Tertiary and immediately overlying the eroded surface 

 of the uppermost Cretaceous strata in East Texas is a great bed of stratified 

 clay, which, on account of its position as the lowermost bed of the Eocene in 

 this region, has been provisionally called the Basal Clays. These underlie a 

 stretch of interspersed prairie and timber land, the country being composed 

 mostly of prairie, with occasional belts and groves of timber. This timber is 

 all hard wood, consisting mostly of post oak, blackjack, and hickory. The 

 belt is sometimes over ten miles wide, and runs between the western edge-of 

 the timber and the Central Texas prairies, from the northern part of the 

 State to the Colorado River and beyond. The stratification of these beds is 

 very characteristic, and is very different from the massive structure of the 

 underlying Upper Cretaceous "Ponderosa Marls," but on a weathered surface, 

 where the stratification is not seen, the clays of the two formations are not 

 easily distinguished.* They consist of a stiff laminated clay, yellow, gray, 

 blue, or bluish-green in color, frequently interbedded with seams and laminae of 

 sand, containing many concretionary masses of gray non-fossiliferous lime- 

 stone, the latter much cut up by veins of brown crystalline calcite, and varying 

 in size from a few inches to six feet in diameter. They are generally of a 

 flat elliptical shape, and of a gray ctflor. Large quantities of gypsum are 

 also found in places in the clay. On Burnet Creek, one mile east of Wills 

 Point, gypsum crystals five to six inches long are frequently found. One of the 

 most constant characteristics of the clay is the presence in it of soft small white 

 calcareous concretions one-tenth of an inch to two inches in diameter, and often 

 having the cauliflower-like form of some of the geyserite of the Yellowstone 

 Geyser basins. These are found very plentifully, and often collect in large 

 quantities in creek beds. No lignite beds have been seen as yet in these clays. \ 

 Such deposits are found well developed at Wills Point, in Van Zandt County. 

 Going east from this place, they are traceable for two and a half miles, when 

 they finally dip under the overlying sandy strata. West of Wills Point 

 similar strata are seen until we reach Rocky Cedar Creek, a distance of five 

 miles. Here is seen a deposit of shell limestone, composed almost entirely of 



* The Basal Clays are probably largely derived from the destruction of the underlying 

 Cretaceous strata. 



f These clay beds probably represent the Eo-lignitic of Heilprin's Eocene section, the base 

 of Hilgard's "Northern Lignitic" in his Mississippi section, and the Arkadelphia Shales at 

 the base of HiU's "Camden Series" in Arkansas. 



