200 CARHOMFKKOUS KOUM ATK )N8 AND KAUNAS OK COLORADO. 



this lauim would indicate tlio (iirbonit'erou.s pcM'iexl without <|ii('stioiK hut recent col- 

 lections from tlie Pcrnio-C'iirbouii'erous of the Wasatch Mountains iiave raised a 

 doubt as lo wiii'thcr the age is really Paleozoic or Mesozoic' 



The Paleozoic section of central Colorado has a maximum thickness of 7,120 feet, 

 made up as follows: Sawatch (luartzite (Cambrian), 601 feet at Eagle River; Yule 

 limestone (Ordovician), 400 feet at Aspen; Parting quartziti; (Devonian ?), 90 feet at 

 Crested Butte; Leadv'ille limestone (Devonian and Mississippian), 525 feet at Ci'ested 

 Butte; Weber shale (Pennsylvanian), 1,000 feet at Aspen; and Maroon formation 

 (Pennsylvanian). 4,500 feet at Crested Butte. In addition to this we have the brick- 

 red series of Red Beds, cpmmonly referred to the Trias, which measures 2,000 feet 

 at Aspen. There are in this series, however, a number of time breaks and some 

 erosional unconformities. The most important instance of the latter is at the top 

 of the Leadville limestone. 



An interesting parallel can be drawn between the Paleozoic section of central 

 Colorado and that of the Wasatch Mountains of Utah, one also which will aid in 

 determining the relation of the former with the Uinta Mountain section. Except in 

 thickness, the Cambrian series of the Wasatch Range is not unlike the Cambrian of 

 Colorado. The Cambrian in each case is followed by a limestone of Ordovician age — 

 the Ute limestone in Utah and the Yule limestone in C'olorado. This again is 

 succeeded by a quartzite series — the Ogden quartzite in Utah and the Parting quartz- 

 ite in Colorado, the age of which is suspected to be Devonian. Then also, in both 

 areas, follows a limestone of Mississippian age — the Wasatch limestone of the Wasatch 

 section and the Leadville limestone of Colorado. In Colorado a Devonian series is 

 included with the Leadville limestone, which I believe to have no equivalent in the 

 Wasatch section. The geologists of the Fortieth Parallel Survey found Upper Car- 

 boniferous fossils down to 5,100 feet below the top of the Wasatch limestone. We 

 may consider, therefore, that the lower 1,600 feet are of Mississippian age and the 

 upper 5,400 feet of Pennsylvanian age. The Mississippian portion of the Leadville 

 limestone can be correlated, not only by its lithology and position in the section, but 

 also almost conclusively by its fauna, with the Mississippian portion of the Wasatch 

 limestone. If the sedimentation which produced the Wasatch limestone was not 

 entirely uninterrupted, the series is at least more complete than that in Colorado, 

 for above the beds whose fauna warrants a correlation with the Leadville limestone 

 succeeded others with an upper Mississippian fauna, which were either never 

 deposited upon the Leadville, or, as I believe more probable, have been lost by 

 erosion. 



The Leadville limestone is succeeded by shales and limestones, unfortunately 

 called the Weber limestone, or Weber shales, which occupy the same position in the 

 section as the upper portion of the Wasatch limestone. Above the Weber in Colo- 



