104 CARBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



siliown on a unique scale in tlii.s lueality. The same may be said, thougli in a less 

 degree, of the vallc}' of the Arkansas as it emerges from the mountains near Canon 

 City. 1 am inclined to ))cli«>ve that it is only in these localities that rocks older than 

 the Triassic or lied Beds are shown along the eastern Hanks of the mountains south 

 of Cheyenne. 1 have looked in vain for a single exposure of well-defined Paleozoic 

 strata from Big Thompson to Colorado City, a distance of over 1()<) miles. I am 

 now convinced that in the North the Paleozoic rocks are often concealed for long 

 distances, although I have usually represented them by colors on a geological map 

 by continuous liands along the mountains. That they exist continuously along the 

 eastci'n margins in Colorado and New Mexico I can not doubt, but only at these 

 specially' favored localities do they appear from beneath the Triassic or Red Beds. 

 They are, however, far more frequeritlj^ exposed farther northward, and I think 

 much more largely developed."" 



Yet a little beyond, on page 133, he mentions the Jurassic Red Beds and the 

 Paleozoic sandstone as occurring in Boulder Valley. 



The actual presence of the older Paleozoics at several points along the Front 

 Range was recognized by Hay den, as is seen in the passages above quoted. It is 

 to one of these occurrences that he refers on page li4, without assigning unj 

 geologic age. On pages 145 and 148, however, he cites Carboniferous beds at 

 Camp Creek Canj^on and at Oil Creek. From the geographic position of these 

 occurrences, and from the fact that practically all the Carboniferous along the Front 

 Range, if Carboniferous at all, consists of Red Beds, which Hayden places in the 

 Mesozoic, and from other associated circumstances, it is fairly certain that the rocks 

 mentioned in all three instances are Ordovician. 



In 1868,* referring to the Red Beds of Colorado and Wyoming, Hayden expresses 

 the belief that their lower portion is of Carboniferous age, and that it is quite possible 

 that a portion is Triassic, while the yellow, graj% and rust}^ sands and sandstone 

 above are Jurassic. This was a preliminar}' statement prepared immediately after 

 the field work which furnished the material for the report above quoted. 



In his atmual report for 1874 Hayden *" again takes occasion to describe the 

 geology of the Front Range. "Up to this time," he says, "we have determined 

 the existence, in this belt in Colorado, of the Silurian, Carboniferous, Triassic (?), 

 Jurassic, Cretaceous, and Tertiarj^ groups; yet, while the more modern formations 

 are very persistent throughout the entire distance from the north to the south line, 

 some of the older beds are wanting in man^r places." From Fort Laramie to 

 Colorado Springs, a distance of over 200 miles, no Silurian beds were recognized, 

 with the possible exception of the variegated sandstones which lie next to the granite 

 at Pleasant Park. 



c Essentially the same view is expressed iu different language on page 139. 



bAm. Phil. Soc., Proe., vol. 10, 1S68, p. 474. 



cD. S. Geol. Geog. Surv. Terr., [Eighth] Ann. Rept., for 1874, 1876. pp. 19-68. 



