468 -R. T. Hill — Uppermost Cretaceous Beds of the 



by the use of alternate currents was always smaller than that 

 obtained by the other method, but the application of the method 

 of alternate currents "'fatigued " all but the so called constant 

 cells. In the cases of most of the cells there was a tendency 

 in what we have called the internal resistance to decrease* as 

 the strength of the current which the cell is delivering increases. 

 Sometimes, however, this tendency did not appear until the 

 resistance of the shunt became very small and the trustworthi- 

 ness of the computed results were in consequence impaired. 



It would be easy to suggest explanations for the results noted 

 here, but we shall content ourselves with calling attention to 

 the facts. 



Jefferson Physical Laboratory. 



Akt. LYIII. — Relation of the Upper?nost Cretaceous Beds of 

 the Eastern and Southern United States, by Robert T. 

 Hill ; and the Tertiary Cretaceous Parting of Arkansas 

 and Texas ; by Robert T. Hill and R. A. F. Penrose, Jr. 



The newest and most easterly outcrop of the marine Creta- 

 ceous formations west of the Mississippi is in the banks of the 

 Ouachita river at the town of Arkadeiphia, Arkansas, where it 

 appears beneath the Tertiaryt and Quaternary^: strata which 

 compose the prevalent and unconsolidated structure of the 

 region. 



This exposure, in the heart of the Atlantic timber belt, and 

 surrounded by later formations is made by erosion, and may be 

 termed a Cretaceous island. Continuing toward the southwest,, 

 the areal exposures of the Cretaceous become more and 

 more extensive until in central and. southwestern Texas they 

 entirely succeed the Eocene sands and forests, and become the 

 prevalent surface formation of the country. They increase not 

 only in areal extent but also in thickness and in number of 

 horizons, so that successively lower horizons are crossed, until, 

 between Arkadeiphia, Ark., and the Paleozoic area of Central 

 Texas can be found a succession of Upper and Lower Cretaceous 

 deposits, aggregating over 5,000 feet, as seen, and which may 

 prove much greater when more accurate measurements can be 

 made. 



' * The apparent resistance of almost any common cell, as obtained by Ohm's 

 method or one of its modifications, is larger when the determination is made 

 with small outside resistances in the circuit than when larger ones are used. 



f The Great Northern Lignitic horizon of Hilgard (Eo-Lignitic of Heilprin). 

 See The Neozoic Geology of Southwestern Arkansas, vol. ii. Annual Report of 

 State Geologist of Arkansas, 1888. 



\ The Plateau Gravel formation. See same as above. 



