CORRELATION OF FORMATIONS 471 



As far as I know, no one has presented evidence of a stratigraphic 

 break within the Red beds or suggested that the conflicting evidence as 

 to age might be explained by such a break. The Ouray unconformity, 

 however, establishes for southwestern Colorado a definite line between 

 Triassic and pre-Triassic portions of the Red beds, which can be traced 

 on a lithologic basis where no visible unconformity exists. From evi- 

 dence which will be presented in following pages it seems certain 

 that the Dolores formation may be positively recognized through its 

 fossils and lithologic character in Utah and Arizona and very possibly 

 in New Mexico. As a step toward a better understanding of the Red 

 beds, I desire to make certain suggestions as to the correlation of the 

 Cutler and Dolores formations with strata in other parts of Colorado, in 

 Wyoming, and particularly in the Plateau province of Utah, Arizona, 

 and New Mexico. The discussion is based on a study of the literature, 

 on recent published discoveries and on unpublished information. Natu- 

 rally much of the correlation suggested is tentative. 



Four principal factors have had influence in this tentative correlation : 



a. The lithologic character of formations compared. — This is the most im- 

 portant on the whole, since it is the only one applicable in all places. 



b. Fossil evidence. — This guide is becoming more and more important 

 as new discoveries are made. Unfortunately, collectors of fossils, and even 

 paleontologists are not always alive to the importance of careful strati- 

 graphic studies and accurate measurement and description of sections in 

 the localities where fossils are obtained. Their work is therefore often 

 shorn of much of the value that should attach to it. 



c. The influence of post- Triassic elevation and erosion. — The stratigraphic 

 break at the base of the La Plata sandstone is one of great magnitude 

 throughout the western portion of Colorado. In several places the 

 La Plata is seen in angular unconformity with the entire Paleozoic and 

 older Mesozoic section. It is possible that synchronous elevation, in 

 gentle folds or low domes, occurred in the Plateau district, but have not 

 been recognized. 



d. The influence of the pre-Triassic elevation and erosion. — While it appears 

 probable that the pre-Dolores uplift was by no means so extensive as the 

 post-Dolores disturbance, it is plain that its influence must be looked for 

 in the Plateau country as well as in the Rocky mountains. 



RELATIONS OF COLORADO FORMATIONS TO THOSE OF THE PLATEAU PROVINCE 



The Red beds and adjacent formations have been described in fore- 

 going pages in the development they possess on the eastern side of the 

 zone between the geologic provinces of the Rocky mountains and of the 

 Plateau country. Even in the small area studied in detail these forma- 



