228 E. B. BRANSON ORIGIN OF RED BEDS OP WESTERN WYOMING 



Sodium sulphate and magnesium are not associated with the gypsum, 

 but are very abundant in most waters of arid regions, and the concentiu- 

 tion could not have reached the place where they would be deposited. 



TIME, EROSION, AND PURITY 



The time necessary for the deposits from fresh water seems prohibitive 

 when it is considered that there is no sign of erosion laterally from the 

 gypsum beds before the next beds were laid down. More or less uncon- 

 solidated sand would erode rapidly and it seems necessary that the 

 erosion time be short. The purity of the beds seems to preclude great 

 length of time. Some sediments must have been brought in by streams, 

 and the winds would have brought in large amounts, but these thick 

 beds of gypsum are in most cases relatively pure from bottom to top. 



General Conclusion 



It is practically impossible for thick beds of pure gypsum to form from 

 fresh water under arid climate conditions. 



Summary 



The following evidences are presented as indicating marine origin for 

 most of the Eed Beds of western Wyoming and the presence of the 

 gypsum as pointing to marine origin for the upper Eed Beds of most of 

 W'^yoming : 



1. Uniformity in thickness of beds over wide areas. 



2. Uniformity in texture of rocks over wide areas. 



3. Eipple-raarking on horizontal beds through most of the formation. 



4. Chemical precipitate of limestone at the 800-foot level. 



5. Chemical precipitate of gypsum near the top over wide areas and 

 at various levels in many places. 



6. Absence of sun ci'acks and fossils of land animals excepting in the 

 Popo Agie beds. 



7. Presence of undoubted subaerial evidences in the Popo Agie beds, 

 with textures and materials like much of the rest of the Eed Beds. 



