FORMATIONS AND PHYSICAL HISTORY 471 



Some of the Red Beds in western Texas, New Mexico, and elsewhere 

 in- perhaps later than Permian, and some in Oklahoma, Kansas, 

 Colorado, and perhaps elsewhere, are older. 



In the Staked Plains of Texas the system has its greatest devel- 



>ment. The oldest part (Wichita formation) is partly of marine 

 ind partly of fresh-water origin. The Middle Permian (Clear Fork 

 linu-stone) is of marine origin, and overlaps the Lower. The Upper 

 'ermian (Double Mountain formation) indicates a reversal of condi- 

 tions, for much of Texas was again cut off from the ocean, and con- 

 , erted into an inland sea or seas, in which the phases of deposition 



)mmon to such bodies of water took place. Occasional beds of 

 limestone- with marine fossils point to occasional incursions of the 



.a, while deposits of salt and gypsum point with equal clearness 

 to its absence, or to restricted connections, and to aridity of climate. 

 Throughout much of the area west of the Rocky Mountains 

 the Permian has not been differentiated. There is, in places, con- 

 formity between the Carboniferous below and the beds classed 

 is Trias above, suggesting the presence of unseparated Permian 

 Between. In northern Arizona and in southwestern Colorado and 

 perhaps at other points, there is an unconformity at the top of the 



'ermian. The Permian system may have been continuous once 

 from Texas to the Great Basin, by way of New Mexico and Arizona; 

 )ut if so, the continuity of the beds has been interrupted by erosion, 

 very considerable thickness of marine Permian (3,800 feet) is 

 reported from Utah. Many Permian deposits of the far west, and 



)me of those in the longitude of Texas and Kansas, are red. This 



>lor characterizes so many formations known to have been made 

 inclosed basins that the connection can hardly be accidental. 

 Thickness. In the Appalachian region, the Lower Permian 

 )eds, sandstone and shale with thin seams of coal, have a thickness 



>f about 1,000 feet. The Upper Permian is wanting. In Kansas 

 the thickness is twice as great, while in Texas it reaches 7,000 feet. 

 Correlation. In the region east of the Mississippi, the Permian 

 is so closely associated with the Coal Measures that the two were 

 formerly classed together, the Permian being called Upper Barren 

 Coal Measures. Were this region only considered, this classifica- 

 tion would appear to be satisfactory. In the western part of the 

 continent the separation of the Permian from the Carboniferous 

 will probably prove to be more distinct, when details have been 

 worked out, and its relation with the Trias close. The Permian 



