I02 



ELIOT BLACKW ELDER 



where subsequently eroded from the crests of the anticlines — it is 

 tolerably safe to assume that western Wyoming, near the close of 

 the Cretaceous period, was a nearly level plain of aggradation very 

 near sea-level, and wholly devoid of outcrops of the Paleozoic and 

 older rocks (Fig. 3). It is deemed unnecessary to apologize here 

 for disregarding the ancient view that each area of Archean out- 

 crops has been an island ever since the Cambrian. 



Fig. 



Post-Cretaceous oro genie disturbance. — -The Cretaceous and under- 

 lying strata have been compressed into a series of folds which gener- 

 ally trend northwestward through central Wyoming, and bend 

 around to the south in the southwest part of the state. The pre- 

 vaihng structures in the district are open anticlines and synclines 

 oversteepened on the southwest sides. Some of the largest folds, 

 such as the Wind River and Gros Ventre anticlines, broke along 

 their southwest flanks and formed overthrusts of large displacement. 

 The most intense folding in this district generally is to be found on 



