THE ORIGIN OF RED BEDS 249 



the slowness of chemical decomposition in polar regions; aridity 

 explains it in the desert, where disintegration is accelerated by 

 great daily range of temperature; and disintegration is acceler- 

 ated on mountain peaks by all of the factors mentioned. Absence 

 of vegetation, which itself is dependent chiefly on climatic factors, 

 is unfavorable to rapid decomposition of rocks because of the 

 important part played by organic acids in the chemical processes 

 of weathering. 



As we have seen, the occurrence of gypsum indicates aridity 

 and high temperatures, so that we may rule out the hypothesis 

 of Arctic conditions as applicable to the Red Beds. The coarse 

 conglomerates in certain parts of the Red Beds are indications of 

 high relief in certain areas and at certain times. 



The occurrence of limestone conglomerate in the Red Beds 

 of the Arbuckle-Wichita region emphasizes the predominance of 

 disintegration over decomposition in that area, as limestone is one 

 of the most readily decomposed of rocks. If the limestone con- 

 glomerates of the Cutler formation were detrital, it would have the 

 same significance concerning the processes of the San Juan region; 

 but it has been interpreted otherwise. 



Evidence supplied by fossils. — It has been stated that marine 

 limestones carrying abundant faunal remains occur in central 

 Texas interbedded with the Permo-Carboniferous Red Beds. 

 The significance of the relations found in this region is well sum- 

 marized by Chamberlin and Salisbury, as follows: 



The oldest part of the Permian system {Wichita formation) indicates that 

 the critical attitude which characterized the surface farther east during the 

 Pennsylvanian period now affected Texas, for the beds are partly of marine 

 and partly of fresh-water origin. These beds are succeeded by a formation 

 of limestone (the Clear Fork) of marine origin, which overlaps the Lower 

 Permian. The Upper Permian {Double Mountain formation) which follows 

 indicates a reversal of relations, for much of Texas was again cut off from the 

 ocean, and converted into an inland sea, or into inland seas, in which the 

 phases of deposition common to such bodies of water took place. Occasional 

 beds of limestone with marine fossils point to occasional incursions of the sea, 

 while deposits of salt and gypsum point with equal clearness to its absence, or 

 to restricted conditions, and to aridity of climate. 1 



1 T. C. Chamberlin and R. D. Salisbury, College Geology (New York: Henry Holt 

 & Co., 1909), p. 661. 



