INTERPRETATION OF ENVIRONMENTAL CONDITIONS 213 



"In conclusion, it seems evident that the Texas 'red beds' were originally 

 maturely decomposed red residual soils formed under warm and moist climatic 

 conditions. In the older 'red beds' there is no evidence of arid conditions; 

 in the later Permian ' red beds ' the residual soils were transported and deposited 

 in arid basins without loss of their color. It is probable that the true origin of 

 all the 'red beds' in the western interior of North America is from residual soils, 

 or the erosion and redeposition without change of color, of older 'red beds." ! 



Tomlinson 1 in a study of the origin of red beds concludes that the red 

 color is original and that the sediments are residual soils derived from 

 elevations formed at the close of the Paleozoic. Specifically he suggests 

 the derivation of the Cutler and Dolores sediments of Colorado from the 

 Uncompahgre Plateau and of the red beds of Arizona and New Mexico 

 from high lands in Mexico, Arizona, and southern California. The Rustler 

 limestone and Castile gypsum he suggests may be deposits in the clear 

 water of inclosed basins. These give place to red beds on the edges of the 

 basins in shallower water. 



For the northern portion of the Plains Province, Richardson* reaches 

 the same general conclusion as to original color and suggests the origin of 

 the material from the Rocky Mountains, washed into a sea which covered 

 the site of the Black Hills. Two possible areas of supply, the Sioux quartzite 

 area of Algonkian age to the east, and the uplifted Pennsylvanian limestones 

 to the east and southeast, are considered, but not regarded as probable 

 sources. However, these may have supplied much material now deeply 

 buried or removed by erosion. 



F. INTERPRETATION OF CONDITIONS IN THE BASIN PROVINCE. 



As is shown in the summary description of the Permo-Carboniferous 

 deposits of the Basin Province, the red beds are confined very largely to 

 the southern portion, occurring in northwestern New Mexico, southwestern 

 and western Colorado, northeastern Arizona, and southeastern and southern 

 Utah; to the north the equivalent horizon is marked by shales, impure 

 limestones, and phosphate-bearing beds. Only in Wyoming do red beds of 

 Permo-Carboniferous age occur in the northern part of the Basin Province 

 The source of the material in the southern portion seems to have been in the 

 elevations now forming the southern ends of the Rocky Mountains, for to 

 the south lay the seas in which were deposited the limestones and shales 

 of the trans-Pecos region in Texas, marine conditions which were apparently 

 continued to the west. As noted above (page 152), Schuchert would place 

 the Kaibab limestone and its equivalents in the Permian or Permo-Car- 

 boniferous. If this suggestion should finally be accepted, the only effect 

 upon the argument of this work would be to indicate that the climatic 

 change arrived in the southern portion of the Basin Province at a later 

 date than is here assumed. 



1 Tomlinson, C. \V., Origin of Red Beds, Jour. Geol., vol. 24, pp. 153 and 283, 1916. 



* Richardson, G. B., Upper Red Beds of the Black Hills, Jour. Geol., vol. II, p. 365, 1903. 



