AGE OF THE ARAPAHOE AND DEXVFK. 24)i 



locality the Ruby formation, one of the apparent equivalents of the 1 >en\ er 

 beds, occurs between the Laramie and the Wasatch. As stated in an earlier 

 part lit' this section, the Ruby formation reaches a thickness of 2,000 feel 

 in the West Elk Mountains. It is also to be borne in mind that in the 

 Anthracite district of ' lolorado there is a formation — the ( )hio ( 'reek — which 

 is the probable though uol demonstrated equivalent of the Arapahoe. 



[f the Castle Gate section be assumed to be the product of continuous 

 sedimentation from the Fox Hills to and including the Wasatch Eocene, 

 as advocated by Dr. C. A. White for certain regions, it is still true that 

 the several time-intervals of the Laramie, Arapahoe, Denver, and also the 

 Puerco, must be represented iii that section, and the < ilaosaurus, having been 

 found in the upper sandstone member of the group of strata referable to the 

 Cretaceous, is most plausibly of one of the post-Laramie epochs. This is 

 rendered still more plausible by the character of the invertebrate fauna 

 occurring below the vertebrate horizon, which is much more closely related 

 to the Fort Union or Wasatch faunas than to any known from unquestion-* 

 able Laramie. 



If the sedimentation was not continuous in the Utah .seas, then then- 

 are stratigraphic breaks in the series of apparently conformable beds. As 

 to the equivalent of the Puerco in the section, it remains to be demonstrated 

 that the Wasatch of the New Mexico section, which rests on the Puerco, is 

 the same as the Wasatch of Utah, as identified hv the invertebrate paleon- 

 tologists. Furthermore, it is well known that while Professor Cope, who 

 has defined and studied the Puerco, refers it to the Mesozoic, as "post- 

 Cretaceous," Professor Marsh includes it with the lower Wasatch Foceiie. 



Bijou Creek, Colorado. About 4< > miles east of |)eliver is the valley of BijOU 



('reek, one of the typical streams of the plains, rising some •_'."> miles north- 

 east of Colorado Springs and coursing a little east of north to the Platte 

 River, a distance of about NO miles. The upper portion of its course is 

 in the Monument ('reek strata, while near its mouth are true Laramie 

 beds, according to Dr. ( '. A. White, 1 who, in 1X77, collected such common 

 Laramie shells as Ostrea glabra, Anomia micronema, Corbula suhtrigonalis, 

 Melania wyomingensis, and several species of Corbicula. From the locality 



Eleventh Aim. Rept. U. S.G.and G. Survey of Terr., p. is:'. 



