ORIGIN OF THE PALUXY SANDS. 511 



occasional areas of reddish saudy lands, bearing a growth of post-oak. 

 Sometimes these localities are very small, and may be seen on one side of a 

 slight valley of erosion but not on the other at the same level. Elsewhere, 

 however, they have a very considerable and unmistakable outcrop, as for 

 instance, near the junction of the northern and Russell forks of San Gabriel 

 river. 



To the northward, the Paluxy sands increase in development, overla])ping 

 interiorward on the Glen Rose and Trinity beds, and abutting against the 

 Paleozoic area in Indian territory from a point west of Ardmore eastward 

 to the Arkansas line, where they occupy the escarpment valley of the basal 

 Comanche Peak beds or Preston limestone. They also appear at Preston 

 bluff, near Denisou. These sands, which the writer has hitherto classed as 

 Trinity, and which may yet prove to be inseparable from them, have been 

 traced out by him during the past year from the Arkansas line westw^ard. 

 At no place in Indian territory east of the 97th meridian do the Glen Rose 

 beds outcrop, and it is my opinion that they still remain concealed there by 

 this uneroded overlap of the Paluxy sands ; for the alternating beds are 

 again exposed beneath them in Arkansas. 



The absence of these sands south of the Colorado-Brazos divide is an in- 

 teresting feature, wdiich can best be explained on the hypothesis that the 

 littoral sedimentation diminished away from the main land area to the south- 

 ward, and by the existence of a buried pre-Trinity and pre-Paluxy topo- 

 graphic protuberance of Carboniferous limestones, which persisted above the 

 Trinity waters in the Burnet area until the basal Comanche Peak epoch, 

 and which extends from northern Burnet and Llano counties eastward into 

 Lampasas county, and w^hicli then divided the country into a northern em- 

 bayment and a southern open sea. The presence of this ridge is shown by 

 the difference of level in the pre-Comanche floor, as exposed by the erosion 

 of the Comanche sediments at Lampasas and Burnet, and also by the hori- 

 zontal deposition of the latter upon its unequal altitudes. This is especially 

 well shown in the profile from Burnet to Smithwick Mills post-office, the 

 Carboniferous floor being revealed in unconformable contact with the Trinity 

 at all altitudes from 650 to 1,200 feet. This Paleozoic barrier of central 

 Texas has little or no arenaceous strata upon its southern side, and hence the 

 absence of the Paluxy sands in that direction, the existence of which would 

 imply the occurrence of a })re-existing arenaceous terrane. These sands 

 mark a return to land conditions in northern Texas at the close of the 

 Trinity epoch, and the beginning of the main great subsidence as recorded 

 in the Comanche Peak, Washita and Denison beds of the overlying division. 

 No fossils have been found in the Paluxy sands, save silicified wood, which 

 occurs in great abundance, and has been mistakenly considered Quaternary 

 in age. 



LXXV— Bull. Geol. Soc. Am., Voi-. 2, 1890. 



