CHAPTER II. 



By George li. Eldbidge. 



MESOZOIG GEOLOGY. 



SECTION I.— THE FORMATIONS. 



TRIAS. 

 WYOMING FORMATION. 

 STRATIGRAPHY. 



Within tlic Denver Basin, lying at high angle of dip along- the base 

 of the Archean slopes and often extending to a considerable height above 



them, is a prominent series of brilliant-red conglomerates, sandstones, and 

 shales, with thin limestones and gypsums in the upper part. These are the 

 well-known Red Beds of the Rocky Mountain region. They are commonly 

 referred to the Trias. The term "Wyoming" is here adopted as their 

 formation name. In the Denver field thev rest directly upon the ancient 

 crystalline rocks, although in man}- other localities there intervene thou- 

 sands of t'eet of Paleozoic measures, Permian ('.'), Carboniferous, Silurian, 

 and Cambrian. 



The thickness of the series exposed in the Denver Basin varies between 

 500 and 3,000 feet, but is generally somewhat under 1,500. The varia- 

 tion is chiefly due to the unevenness of the ancient floor upon which the 

 formation was laid down, the Archean having been thrown into folds and 

 having suffered extensive denudation before the deposition of the younger 

 formations upon it. 



In the southern half of the area mapped the topography of the Red 

 Beds is that of a longitudinal valley between an Archean mountain slope 



