50 THE PERMO-CARBONIFEROUS RED BEDS OF 



As shown above (p. 45; see also p. 104, below), the greatest number of 

 plant remains, and the greatest abundance of iron-free deposits, and deposits 

 with ferrous rather than ferric iron, occur closely associated with the Clear 

 Fork limestones. The series of limestones and associated light-colored clays 

 are separated by beds of red color, high in ferric oxide. This indicates a 

 decided fluctuation in the climate. The cause of this fluctuation is far from 

 apparent. In lack of a better explanation the variations in climate are 

 tentatively associated with the recurrent invasions of the sea from the south. 

 It is conceived that the dominant condition of the whole area, and a wide 

 surrounding region, was semiaridity, with a somewhat higher degree of 

 humidity on the highlands of the ancient Wichita Mountains. When the 

 seas spread in wide and shallow bodies over the flat land and reached far 

 toward the mountains, the waters of the lagoons, estuaries, and pools upon 

 the borders of the advancing sea were warmed, and a large quantity of water- 

 vapor rose in the air, but the relative humidity was not increased, since the 

 amount of water -vapor which may pass into the air with a rising temperature 

 is always greater than the amount actually evaporated. If, for some reason — 

 cyclonic or monsoonic effects, for instance — this air with its really large 

 content of water-vapor was drawn across the high land of the neighboring 



Fig. 8. — Diagram illustrating advance of the "Albany" sea over Wichita and Clear Fork 

 deposits, showing how the presence of the water precedes the deposits and possibly- 

 affected precipitation on land from which deposits were derived. 



Wichita Mountains, the cooling of the air would cause an abundant precipi- 

 tation on the slopes. This water would pass out upon the flats adjacent 

 to the ocean border, increasing the volume of the streams, raising the water- 

 table, and inducing a much greater plant growth. The decay of this vege- 

 tation would furnish the carbon necessary to reduce the ferric oxide present, 

 or would exhaust the free oxygen, which would otherwise result in the for- 

 mation of ferric oxide. The carbon dioxide formed would leach out the iron 

 already deposited, and white or gray iron-free beds would result, or beds with 

 ferrous iron, green, blue, or purple. 



These conditions would exist in front of the advancing sea, and the iron- 

 free clays would be below the limestones, as they always are. When the 

 reverse change occurred, following the retreat of the sea, the local evaporation 

 would decrease, the supply of moisture decrease, the vegetation fail, and 

 red-colored rocks would again predominate. 



If, as conceived, the oscillations of level were due to tilting, with the 

 axis of tilting south of the Wichita Mountains, the depression of the plain 

 would be accompanied by an elevation of the mountains, accentuating the 

 conditions described; but this movement was never very great in either 

 direction. 



