'240 CARBONIFEROUS FORMATIONS AND FAUNAS OF COLORADO. 



The same formatioii.s occur in l)oth areas, as I hnw already said, hut tlio. nomen- 

 clature adopted in the Teninilc folio differs from that of the Leaclviilc monograph, 

 which preceded it hy twelve years. The Uppiir Carboniferous formations of the 

 Lcadville monoo-raph iire called the Weber shales, the Weber grits, and the Upper 

 Coal Measures. In the Tenmile folio these are called the Wel)er shales, the Weber 

 grits, and the Maroon formation. In fact, the Weber shales and Weber grits are 

 united as the Weber formation. Above the Weber grits a third formation is dis- 

 criminated as the Wyoming formation, whose age may be Carboniferous, but is not 

 detinitelv known. In addition to this, two of the limestones included in the sand- 

 stones and conglomerates of the Weber and Maroon formations proved of sufficient 

 local importance to receive distinct names. The Robinson limestone l)elow and the 

 Jaccjue Mountain limestone above are assigned as the bounding beds of the Maroon 

 formation. It will be noticed that the geologic sequence here is similar to that in 

 the Crested Butte quadrangle, 1uit though the same names have been employed in 

 some cases, and apparently the same formations differentiated, the names are used 

 in a somewhat different sense, a course which is to be deprecated as very confusing. 



For the lowest Pennsylvanian horizon in the Leadville and Tenmile districts 

 the name Weber shale has been adopted, as I have alreadj- said. The formation in 

 this area has a thickness of about 300 feet, and consists of calcareous and argillaceous 

 shales alternating with quartzitic sandstone. The Weber grits have an average 

 thickness of 2,500 feet, and consist of sandstones and conglomerates, with a few thin 

 shales and dolomitic limestones. The source of this material is said to be the 

 Archean. The Maroon formation is similar to the Weber grits in constitution, but 

 contains a larger proportion of shales and limestones. The latter are nonmagnesian. 

 Its limits are taken as the Robinson limestone below and the Jacque Mountain lime- 

 stone above, and its thickness 1,500 feet. The Wj'oming formation consists of 

 brick-red sandstones 1,500 feet in thickness. No fossils are known from it. 



Twenty -eight collections were obtained in the Leadville and Tenmile districts in 

 connection with the work for the .Tenmile folio and Leadville monograph. These 

 are stations 2250-2277, inclusive, of which 2260, 2261, 2272. 2273, 227i, 2275, and 

 2276 are from the Tenmile district, tlie rest from the Leadville district. Stratigraph- 

 ically these have been distinguished as lower, middle, and upper Weber, Robinson 

 liiriestone, and Maroon formation. The lower Weber corresponds to the Weber 

 shale of the two reports above mentioned, the middle and upper Weber to the 

 Weber grits formation. The Robinson limestone forms the division between the 

 Weber grits and the Maroon formation. The Maroon is, in a general way, the same 

 as the Upper Coal Measures of the Leadville monograph and the upper division of. 

 the Maroon of the Crested Butte folio, the lower division of the Maroon finding 



