H. T. Hill — Texas Section of American Cretaceous. 301 



Within the Central denuded area this newly defined group of 

 the American Cretaceous is beautifully shown, every foot of 

 its thickness and that of the Paleozoic strata upon which it 

 generally rests, having been exposed by the excessive atmo- 

 spheric denudation, showing its contacts with the over- and 

 underlying formations. The process of this denudation in 

 Texas is exactly similar to that of the high plateaus of Utah 

 and Colorado, and the description given by Powell of aridity 

 and erosion in his "Exploration of the Grand Canons of the 

 Colorado," pp. 170-171, is equally applicable to it, except 

 that here in Texas the sudden heavy rainfalls are more fre- 

 quent, and the different resistance of the sedimentary rocks 

 causes a difference in topographic effect. In my paper on the 

 Cross Timbers I have sufficiently described the northeast quar- 

 ter of this central region and shown how the strata in going 

 from east to west, are successively exposed in descending series 

 from the marine Tertiary to the Paleozoic. The latter are 

 exposed along a north and south axis, from the Red River to 

 Colorado, by the removal of the overlying Cretaceous. The 

 northwest quarter of the region is occupied by the red beds, or 

 alleged "Jura-Trias," with occasional patches of the Cretaceous 

 preserved upon it, in the shape of isolated buttes. 



The southern half is still covered by the chalky limestones 

 of the Comanche series of the Cretaceous, which, in addition to 

 having been thicker originally than in the northern portion, 

 have not suffered so much from the destructive denudation. 

 The thickness of this formation rapidly decreases to the north- 

 ward and I am inclined to believe that the strata in Texas and 

 the Indian Territory represent only the northern shallowing of 

 the great sediments developed more fully in Mexico and Cen- 

 tral and South America. The thickness of the Comanche 

 series, while not exceeding 500 feet along the Fort Worth 

 section, at Austin must be fully 2,000, and still farther south- 

 westward I believe it must approach 5,000. In the southern 

 portion of the region the individual strata, as seen at the mouth 

 of the Pecos river, are hundreds of feet in thickness ; at Austin 

 the thickest strata do not exceed fifteen feet, while at Fort 

 Worth and Denison they seldom reach two feet. The members 

 of this series possess sufficient diversity to divide it into many 

 minor divisions, but this should not be attempted until several 

 years more of thorough stratigraphic study of the whole is 

 made. Provisionally I have divided it into a lower and upper 

 division which are called the Fredericksburg* and the Washita 



* See " Texas " and " Kreidebildungen von Texas ?" for the first descriptions of 

 the Fredericksburg strata, by Dr. Ferd. Roemer. The Washita strata are first 

 mentioned by Dr. G. G. Shumard in Marcy's Exploration of the Re d river of 

 Louisiana, but better defined by Marcou in the Pacific Railroad Report of the 32° 

 Parallel, octavo edition. 



