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96 UNIVERSITY OF COLORADO STUDIES 



Mesozoic 



Cretaceous 

 Upper Cretaceous 

 Post Laramie 

 j Denver Beds 

 I Arapahoe Beds 

 Laramie 

 Montana 

 j Fox Hills 

 I Fort Pierre 

 Colorado 



Niobrara 

 Fort Benton 

 Dakota 

 Lower Cretaceous 

 Como 

 Kootenay 

 Jura-Trias 

 Jurassic 

 Triassic 

 Paleozoic 

 Permian 



The Cenozoic is not represented in this area by deposits of any 

 importance, the Tertiary not being found at all. The Lower Creta- 

 ceous is also missing, or at least unrecognized. The time interval and 

 enormous erosion between the Laramie and Post-Laramie would indi- 

 cate that the latter should be assigned to the Tertiary instead of the 

 Cretaceous, but there is paleontological evidence making it advisable to 

 leave the arrangement undisturbed until all the evidence of various kinds 

 is further studied with the idea of harmonizing it, if possible. In any 

 event, the Denver and Arapahoe beds are entirely missing from the 

 Boulder area, though well developed a number of miles to the south. 

 The Permian is not positively known in this region. At Boulder the 

 formations are very nearly vertical, except the Montana, in consequence 

 of which they occupy but a comparatively narrow strip along the edge 

 of the foothills, except the Montana, which, being more nearly hori- 

 zontal and of enormous thickness, covers a strip several miles in width. 

 Northward all the formations flatten out rapidly, widening the outcrops. 



