succession of events 229 



Succession of Events 



1. The Eed Beds began nnfler marine conditions and the sea gradually 

 became more and more charged with calcium carbonate and magnesium 

 carbonate until a dolomitic limestone was precipitated. 



2. Above the limestone the sea gradually filled with sand until the 

 sediments were exposed and the Popo Agie beds were formed under sub- 

 aerial conditions. 



3. The sea in Upper Triassic time readvanced and some 200 feet of 

 sandstone and shales filled the western margin. 



4. Subaerial deposition, mainly of wind-blown sand, succeeded and 

 lasted while beds varying from a few feet to 60 feet in thickness were 

 deposited, 



5. The sea readvanced, but concentration of calcium sulphate had been 

 in progress for a long time and soon resulted in wide-spread deposits of 

 gypsum. 



6. Usually some sandstone and some thin layers of limestone were 

 deposited above the gypsum before the withdrawal of the sea at the close 

 of the period. 



Age of the Eed Beds 



The age of the upper Red Beds in western Wyoming deserves passing 

 notice, though Williston^* has recently stated the evidence. The writer 

 and his parties have never found a fossil in the formation outside of the 

 Popo Agie beds. From these beds Williston^^ has described four genera 

 of reptiles, one closely related to Keuper forms of Europe and the others 

 to South African forms. Tlic writer has described^" two species of 

 amphibians similar io Kciijicr foi'ms of Europe, and Mehl has described^^ 

 a phytosaur similar to those of tlio Keuper of Europe and Newark of 

 North America. To any one fa mil in i' with Triassic reptiles and am- 

 phibians the evidence of tlio Upper 'I'riassic age of the Popo Agie beds 

 is conclusive. 



Below the Popo Agie beds no evidence of a break in the continuity 

 has been seen by the writer a.nd it is possible that the sedimentation was 

 continuous through Upper Permian and Lower Triassic. As mentioned 



« Jour. Geol., vol. 17, p. 396. 



= .Tour. Geol., vol. 12, pp. 688-«r»6. 



'^ .Tour. GpoI., vol. l."'.. pp. .''.60-.'')S0. 



=^Jour. Geol., vol. 21, pp. 186-101, 



