NOTES ON THE LIONITIC GROUP OF EASTERN COLO- 

 RADO AND PORTIONS OF WYOMING. 



By F. V. Haydex. 



The difference of opiuion that has arisen iu regard to the age of what 

 I have hitherto called the Liguitic group in the West, cansed me, during 

 the past summer, to examine again the old areas iu part, especially along 

 the eastern slope of the Rocky Mountains in Colorado. The principal 

 object I had iu view was to determine as carefully as possible the 

 stratigraphical relations of the coal-strata with the purely marine beds 

 below. During the summer, I traced, with much care, the junction of 

 these groups from Cafion City northward to Cheyenne on the Uuiou 

 Pacific Eailroad, and theuce along the railroad westward to Green 

 Eiver. As the largest development of the Lignitic group occurs in the 

 vicinity of the railroad iu Western Wyoming and Eastern Utah, it 

 seemed important that this region should receive as much attention as 

 possible. 



We may state here in general terms that along the eastern base of 

 the Eocky Mountains in Colorado, from the Eaton Hills north to 

 Cheyenne, there are no strictly marine coal-beds, and it is probable that 

 they are all of brackish-water origin. As the entire thickness of this 

 group in Eastern Colorado is estimated at about 3,000 feet, some of the 

 upper beds may yet be found to contain well-marked fresh- water shells, 

 but up to this time none have been reported as known from this entire 

 area. Th'e brackish-water shells have come for the most part from the 

 lower beds. 



We may consider for a moment the relations of the Canon City group 

 to the underlying Cretaceous series. We find near the base of the 

 mountains, near Caiion City, on the Arkansas Eiver, a fine development 

 of the entire series of the Cretaceous, from the Dakota group to the 

 summit of the Fox Hills group. No. 3, or the Niobrara group, is 

 especially well shown in the uplifted ridges near the base of the mount- 

 ains around Caiion City, and along the Arkansas Eiver between Caiion 

 City and Pueblo. For a distance of about ten miles below Caiion City, 

 on the river, jSTos. 4 and 5 are quite distinct; No. 4, composed of dark 

 shaly clay, gradually passing up into a yellow arenaceous clay, and 

 finally a laminated sandstone and clay to the lower sandstones of the 

 coal group. If we follow up the dry beds of the little branches which 

 lead into the Arkansas Eiver from the coal area, we can note very dis- 

 tinctly the gradual change in the character of the sediments, showing the 

 approach of shallow water and dry land. There are about 300 feet of the 

 peculiar laminated sands, clays, and sandstones, largely concretionary, 

 sometimes with layers of massive sandstone 13 to 30 feet thick, then 

 thinning out or disappearing altogether, and a loose arenaceous clay 

 taking their place. On this intermediate series of strata, an irregular bed 

 of sandstone rests, varying from 50 to 200 feet in thickness, which we 

 regard as the lowest bed of the Lignitic group. In this sandstone are 



