320 R. T. HILL — GEOLOGY OF RED RIVEK. 



Exteriorly the stone looks very unpropitious for foraminiferal remains, 

 but, so far as examined, it is more largely composed of them than any 

 rock I have seen in the whole series. It is an altered chalk. In one 

 thin slice I have recognized definitely Rotalia, Textidaria and fragments 

 of three or four more genera of foraminifera. 



The outcrop of this formation is proportionately very limited, being 

 better displayed at Austin than at any other locality where I have seen 

 it. North of the Colorado it disappears by faulting until the San Gabriel 

 is reached, near Round Rock, in Williamson county. It outcrops north- 

 ward, according to" TafF, at various points, constantl}^ thinning until it 

 finally disappears near Bosqueville, McLennan county, " where it is only 

 two feet thick." North of the Brazos it has disappeared entirely, and 

 its place in the columnar section is taken by the Dakota (Lower Cross 

 Timber) beds, which do not occur south of the Brazos, but thicken north- 

 ward from that stream, just as the Shoal creek limestone thickens south- 

 ward. 



The Third Annual Report of the Texas Geological Survey definitely 

 stated that this bed does not appear north of the Brazos ; * but in the 

 Fourth Annual Report an entirely different bed,t the Main street lime- 

 stone of this paper, north of the Brazos, has been called the Shoal creek 

 (Vola) limestone, thereby adding confusion to the subject. A careful 

 perusal and comparison of the two Texas reports will show that no 

 paleontologic and stratigraphic proof is offered in the last paper men- 

 tioned for extending the Shoal creek limestone north of the Colorado. 

 Neither is there any justification for placing the Shoal creek (Vola) lime- 

 stone in the Kemp section of trans-Pecos,J Texas. It has been noted 

 southward of Austin by the Texas Survey. 



The Shoal creek limestone rests abruptly, without gradation, upon the 

 Exogyra arietina clays wherever I have observed it. At Austin it is sur- 

 mounted unconformably by the Fish beds — a greatly attenuated southern 

 extension of a persistent horizon of the upper part of the Eagle Ford 

 shales — and at one place (the foot of Pecan street) by the Austin chalk 

 (Niobrara), showing a clear unconformity between them. 



The abrupt manner in which the Shoal creek limestone succeeds the 

 Exogyra arietina clays at Austin and the marked faunal difference be- 

 tween them is indicative of a sudden physical change in sedimentation, 

 and, were it not that there is a more marked unconformity between 

 the Shoal creek and the overlying Benton beds, I would be inclined to 

 place the former in the Upper Cretaceous series rather than in the Lower, 

 although, paleontologically, it differs from both. 



* Fourth Annual Report Geological Survey of Texas, 1893, pp. 277, et seq, 

 t Third Annual Report Geological Survey of Texas, 1892, pp. 348, 349. 

 X American Geologist, December, 1892, 



