66 CAKHONIFEROUS FORMATIONS AND KAUNAS OK ('oL(iRAl)O. 



Prococdiny in tho inamicr nlrcady outlinod, the coiiihincd Leadville and Weber 

 foi'iuations, accordiiii;- to Pcale's sections, wouki have an approximate thickness of 

 from 1.200 to 1,7(10 feet. Assuming 300 feet for the Leadville limestone (this 

 formation measures 350 feet at Aspen and 200 feet in the Tenmile district), and 

 accepting- about the mean of the measurements for the combined thickness of the two 

 formations, in the neighborhood of 1,000 feet would then have to be assigned to the 

 Weber formation. The Maroon, according to the above calculations, measures about 

 4,800 feet, and the Wyoming 1,500 to 1,800 feet. 



Comparing the Carboniferous formations in the three sections discussed, it is found 

 that their relative thickness is as follows: Leadville limestone, at Aspen 350 feet, on 

 Eagle River 300 feet (assumed), in the Tenmile district 200 feet; Weber formation, 

 at Aspen 1,000 feet, in Peale's section 1,000 to 1,200 feet, in the Tenmile district 300 

 feet; Maroon conglomerate and its e.ciuivalents, at Aspen 4,000 feet, in Peale's section 

 4,300 feet, in the Tenmile district 4,000 feet; Wyoming formation, at Aspen 2,600 

 feet, in Peale's section 1,500 to 1,800 feet, in the Tenmile district 1,600 feet; the 

 upper limit of the Wyoming formation being an unconformity in each case. The 

 total thickness of the Upper Carboniferous would then be, at Aspen, 7,600 feet; in 

 Peale's section, about 7,500 feet, and in the Tenmile district 5,800 feet. The greatest 

 variation in individual formations appears to be in the case of the Weber and 

 Wyoming formations. The Maroon remains remarkably constant in thickness, 

 though apparently very variable in lithologic detail. The Leadville also varies 

 proportionately in thickness, being at Aspen nearly twice as much as in the Tenmile 

 district. Variations in the thickness of the constituent formations and of the mass 

 as a whole ma}^ be due to erosional unconformities, one of which followed the Lead- 

 ville, while others possiblj^ intervened between the Triassic and the Maroon and 

 between the Weber and Maroon formations. 



Stevenson's report for the One Hundredth Meridian Survey " upon his district in 

 central Colorado covers much of the area which was worked by Marvine, Peale, and 

 others. He describes several sections made in the Grand River, Elk Mountain, and 

 South Park regions, one of which (that on the forks of Eagle River) must have been 

 taken very near the outcrops which furnished Peale's section just discussed. Just what 

 streams are intended to be indicated by the north and south forks of Eagle 

 River I have not been able to ascertain, but the section must be located, as I have 

 said, very near that which Peale worked out on Eagle River near the mouth of Roche 

 Moutonnee Creek. 



The exposures of the Silurian are said to be exceeding!}' fine on the South Fork 

 of the Eagle River, and to diiler little from those of Bald Peak. They appear to 

 consist of massive, dark quartzite, which rests upon granite (page 360). No detailed 



aV. S. Geog. Geol. Expl. Surv. W. 100th Mer., Kept., vol. 3, 1S75, pp. 303-501. 



