806 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



important clues to the age of the formation. At Sour Lake, Texas, they lie beneath beds of 

 known Pleistocene age and above beds of known Miocene age, a position which would fix their 

 age as Pliocene. This is also in accord with evidence from other sources." 



In the region of Austin and San Antonio three distinct terraces flanking the rivers are 

 recognizable. The highest and oldest of these occupy the divides, and the material consists 

 almost entirely of fiint embedded in a calcareous matrix. This is the Uvalde formation of 

 Hill **"* and corresponds to the Lafayette of more easterly areas. It consists of the products of 

 destruction of the Edwards limestone. This material is now found only in the divides of the 

 Coastal Plain, but it constitutes the uppermost terrace in the canyons of the Edwards Plateau. 



The terraces of the second series occupy a lower level and are therefore younger than the 

 Uvalde terraces. The materials composing these in the vicinity of Austin consist of granitic 

 debris derived from the granites of the Llano region, which was exposed only after the Cretaceous 

 cover was removed. In a terrace along Onion Creek, just west of Pilot Knob, Travis County, 

 occur vertebrate remains of early Pleistocene age.^"""* This would make the upper terraces 

 pre-Pleistocene. 



The Uvalde formation is present from Austin to Rio Grande along the interior margin of 

 the Rio Grande plain and extends many miles seaward. For further description see Hill 

 and Vaughan.^*' 



PLEISTOCENE. 



For the areas bordering Mississippi River the brief description given on page 813 will 

 apply. In southern Louisiana the Port Hudson attains a great thickness — usually over 1,000 

 feet and in places over 2,000 feet. This is also true of the Pleistocene of the coastal region of 

 Texas. Landward from the border of the coastal prairies of Texas there are two systems of 

 terraces between the level of the present flood plains and that of the Uvalde formation. 



G 17, H 16-17, I 15-17 (EAST OF MISSISSIPPI RIVEB), AND J 16. SOUTH ATLANTIC AND EAST- 

 ERN GULF COASTAL PLAIN AND NORTH END OF MISSISSIPPI EMBAYMENT. 



The following discussion (pp. 806-813) has been compiled by T. W. Vaughan 

 from the literature and from unpublished results of G. C. Matson and E. W. Berry- 

 in southern Alabama and Mississippi and of his own researches. The principal 

 references to the literature have been listed in Chapter XVI (p. 731). To the 

 list there given may be added Nos. 566, 653, and 693 of the bibliography on pages 

 840-865. 



MIOCENE. 



Vaughan *'* describes the subdivisions of the Miocene along the Georgia-South Carolina 

 line, their correlation with formations farther north, and their relation to the upper Ohgocene: 



"The following section of the exposure at Porters Landing is adapted from the description 

 of it given by Mr. Earle Sloan in his 'Catalogue of the mineral localities of South Carolina,' 

 page 273 : 



Feet. 

 6. Pleistocene — white, red, and yellow sands, with phosphatic pebbles and vertebrate fragments 



at the base 64 



5. Miocene — compact yellow fossiliferous marl (Duplin horizon) 6 



4. Miocene — grayish fossiliferous marl (Marks Head marl) 29 



3. Fine-grained laminated shale with sandy partings: a line of rounded pebbles at the base. . . 14 



2. Oligocene — fossiliferous marl (Alum Bluff formation) 4 



1. Laminated drab shale with arenaceous partings 8 



1114 



"Recent collections made at Porters Landing have rendered possible definite correlation 

 of the two Miocene horizons with those of the area farther north. From, bed No. 5 of the section 

 34 identified species were obtained, 30 of which also occur in the Duplin marl of North 



