ENDLicH.] CONCLUSION — CAEBONIFEKOUS — TRIAS. 107 



former. Dr. Peale* has recognized a Permian or Permo-Carboniferous 

 division. In my districts I have not observed this. Throughout the 

 State the Carboniferous formation is well characterized by fossils, suffi- 

 ciently to set at rest all doubt regarding the identity of the groups. It 

 may be noticed that Carboniferous beds have in Southern Colorado been 

 subjected to considerable contortions. Plications of a complex nature, 

 faulting, and overturns denote the exercise of an enormous force. So 

 far as can be determined, these disturbances must have taken x>lace 

 during a period of time subsequent to the deposition of the older Creta- 

 ceous beds. Unless it is possible to extend observations over a large 

 area it will be no easy matter to recognize this fact. Carboniferous, 

 waters seem to have covered almost, if not entirely, the area occupied 

 before then by Silurian and Devonian deposits. From this it may be in- 

 ferred that, within the regions under discussion, no appreciable disturb- 

 ances can have taken place before the advent of the Carboniferous period. 

 Although a large mass of sediment had been deposited before the Meso- 

 zoic era, yet plutonic activity seems to have remained almost dormant 

 up to that period. We find very little evidence of any old eruptions 

 which in other continents are not wanting. 



A number of ranges are composed largely of Carboniferous strata. 

 Among them the upper group — Arkansas sandstone — forms a very 

 prominent feature. The Sangre de Cristo Range is flanked on either 

 side by beds belonging to this series, and elsewhere similar cases may 

 be observed. Any attempt at parallelizing the Carboniferous forma- 

 tion of Colorado with foreign standards is a thankless task. We have 

 our own peculiar arrangement and cannot readily compare it with any 

 other known. 



TRIAS. 



Usually the Jura and Trias of Colorado are combined in any descrip- 

 tion given thereof. After reviewing all available material I have come 

 to the conclusion that it is perfectly justifiable to separate them. A 

 total absence of paleeontological remains within the limits ascribed to 

 the Trias is very much to be regretted. Could any characteristic fossils 

 be found, it would set at rest the question of age. Jurassic beds exist 

 in the western portion of our continent, and the only doubt remaining 

 is whether or not the " Eed Beds" should be added to the Jura. The 

 total absence of fossils in the Eed Beds argues primarily against the 

 fusion. Lithologically, of course, the differences between the two are 

 very great. First of all, this very characteristic led to the identifica- 

 tion as Trias. 



In case any comparison between the beds of our Western Trias with 

 that of Europe were attempted, we would find that it agrees remarkably 

 well with the youngest member of the same European formation. The 

 "Keuper" of Germany — "Marnes iris6es" of France — show the same 

 detail features that we observe in the West. Arrangement of strata, 

 retrographic and chemical constitution thereof are almost identical. It 

 is certainly not admissible to identify formations by their physical 

 characteristics alone. Taking into consideration, however, the super- 

 position of Jurassic beds in connection with such features, the division, 

 once made, may be sustained. 



All along the Front Range the Triassic beds occupy prominent, simi- 

 lar positions, until towards the south they no longer appear ; west of 

 the Front Range they also occur, but not so continuous as at the locality 

 first mentioned. It appears that at but very few places the Triassic 



* Kep. U. B. Geol. Surv., 1674, p. 117. 



