3 [2 R. T. HILL — GEOLOGY OF RED ElVER. 



and other marine mullusca in association with lignite and the character- 

 istic flora. As a whole, it records the littoral debris accompanying the 

 great oceanic invasion of the Great Plains region in Upper Cretaceous 

 time. It is important to note also that the Dakota is a glauconitic for- 

 mation, and I believe this is the first time that fact has been clearly 

 announced. The intense ferrugination is derived from the oxidation of 

 this glauconite, as clearly shown at Pine bluff, and the glauconite bed 

 which outcrops in clearest purity at Morris ferry of Little river in 

 Arkansas * belongs to the Dakota. 



The Eagle Ford shales, or Benton outcrop, is along the strip of land 

 immediately south of the Dakota, and usually follows the south side of 

 the Red river valley. The variations of outcrop are shown upon the 

 map. They have no determinable outcrop in Indian Territory that isi 

 separable from the Dakota, except at Carriage point prairie, north of 

 Denison. 



The outcrop of the Austin chalk does not deflect eastward down Red 

 river on the Texas side, but it has apparently been cut off by the Cooks 

 springs fault, and the area which should be its normal outcrop is occu- 

 pied by the higher beds of the Glauconitic division, which constitutes 

 all the Cretaceous outcrops of the Red river counties south of the trans- 

 continental branch of the Texas Pacific railroad, east of Grayson county. 



The areal development of the Glauconitic division in Texas is almost 

 entirely confined to the area embraced upon our map. As its beds to 

 the southward are more and more overlapped by the Tertiaries, they 

 only occur in a few isolated and exceptional localities. Its exposures in 

 Fannin and in Lamar county are best explained upon the plausible 

 hypothesis that its outcrops are on the " uplift " block in the angle of 

 the two great fault systems — the Balcones and Red river. 



There can be little doubt but that during the Pleistocene and late Terti- 

 ary time the Sulphur and the Red river valley and those of the northward 

 lateral drainage of the latter were the scene of oscillation, accompanying 

 baseleveling and estuarine deposition. The ancient alluvial deposits 

 certainly belong to several well defined epochs of baseleveling and ero- 

 sion somewhat similar to yet more complicated than those of the Poto- 

 mac region. The Plateau gravel, w^hich is the oldest of these, was laid 

 down at a time when sealevel was 500 feet lower than toda}^, and the in- 

 terior margins and continuity of this formation has been so destroyed 

 by the development of subsequent drainage upon and across it that 

 no detailed hypothesis of its origin can be given until more minutely 

 studied. The sheet as a whole represents the connected deposition of 

 many streams which reached baselevel near the line of its present 



*See Neozoic Geolog;y of Southwest Arkansas, p. 89. 



