INTERBEDDED QFARTZITES. 



91 



3 :r^ 



feet— resting unconformably on tlie Archaean, and underlying Silurian and 

 Carboniferous limestones ; and this is considered -by King, Hayden, and 



Bradley to be Potsdam,* though no fossils are found 

 in it. The Rocky Mountains of Colorado also con- 

 tain in many places similar quartzites with the same 

 relation to the older rocks. Peale has studied them 

 in the Park range, and besides the basal quartzites 

 here alluded to finds other beds intercalated with the 

 sandstones he regards as Potsdam. In a continua- 

 tion of the Organ Mountains, near El Paso, Tex., 

 Jenneyt found a quartzite 25 feet in thickness, rest- 

 ing upon the granite and overlaid b}' beds of Potsdam 

 well characterized by fossils. 



These citations suffice to show the wide-spread 

 development in the Rocky Mountains of quartzites 

 at the base of the Paleozoic system, and the una- 

 nimity with which they have been referred by the 

 best authorities to the Potsdam sufficiently warrants 

 the same reference of the basal quartzites in the 

 southern part of the Hills. 



The quartzites found in the body of the forma- 

 FiG. i;5— Section of tiie i'ots- tiou differ somewhat in their character from those just 



(lam on Box Elder Creek. , •! i mi i i i t i 



1. Slates inclined at a high fiGscribed. 1 hey Were bcst observcd and studied on 



2. Coarse sandstone and Kox Elder Creek in the scctiou illustrated by Fig- 



gravel conglomerate. ^ ~ 



3. Broad talus, no exposure. Ure Id. 



4. Cliff of coarse red sand- /-\ ^ i • i -i /■ i 



stone Avith iuterstrati- On the samc creck, some eight miles farther west, 



fiedlavers of dense, hard, ^^ ro r i i /••i-i 



deep red or purplish a clifi of red saudstouc 30 fcct in height at the 



quartzite. 



5. Talus with fragments of top of the formation coutaius six or eight strata of 



the shaly impure lime- 



stone of the Carbonifer- hard, purplisli, glassy quartzitc from 6 inches to 1 foot 



6. Carboniferous limestone. Ju thickneSS. 



Intercalated quartzites are also seen on French Creek where the color 

 is yellowish brown, and the rock seems to be little more than a fine quartz 



* Mining Industry, 40th Parallel Survey. King. Chap. vi. Geological Survey of the Territories, 

 1871. Hayden; p. 15; /6i(?., 1872. Bradley, p. 194. 



t American Journal of Science. 3d series, vi, 1874, p, 25. 



