RECAPITULATION OF PALEOZOIC FORMATIONS. 167 



several circumstances unite to cast suspicion upon the Mississippian determination 

 for the Red Wall, collections of fossils more recentlj^ made demonstrate that the 

 lower portion at least belongs to that epoch. The Penns_ylvanian age of the upper 

 portion, however, is unmistakabh^ shown b}^ the faunal list supplied by Meek, and 

 since the upper Mississippian is usually missing in the western sections, owing to 

 Pennsylvanian erosion (or possiblj^ to nondeposition), it seems probable that the 

 formation is divided b\' an unconformitj^ otherwise undetected. Furthermore, Powell 

 claims to have traced the Red Wall into the Umta Mountains, where, both by its 

 somewhat ambiguous fauna" and bj^ its stratigraphic position above the Uinta sand- 

 stone, which Emmons correlates b}' tracing with the Weber quartzite, whose Pennsyl- 

 vanian age throughout is satisfactoril}^ known, it belongs, with little doubt, in the 

 Upper Carboniferous. If the Leadville limestone occurs in the Uinta Mountains it 

 must be as one of the siliceous beds of the Uinta sandstone and not as the Red Wall 

 limestone as identitied bj' Powell; but since this horizon is so persistently character- 

 ized bj' its calcai'eous nature it seems somewhat more probable that Mississippian 

 time is unrepresented in the Uinta series of rocks. 



Along the eastern margin of the Front Range the Mississippian limestones 

 appear in several places. It is in this tract called the Millsap limestone. The Mill- 

 sap limestone was first described in the Pikes Peak folio, from which 1 abstract the 

 following: It consists only of local remnants resting upon the Fremont limestone in 

 Garden Park and along the western line toward Canyon. It is represented by about 

 30 feet of thinly bedded, variegated, dolomitic limestone, with a few thin sandstone 

 layers. Chert nodules in the upper limestone layers carry casts of Spirifer rocky-- 

 montanus and Semlnuhi mhtilUa. It is divided from both the formation which 

 preceded and that which followed it by an erosional unconformity. This formation 

 is found also at Perry Park, where both Peale and Lee have made sections including 

 it. These sections have already been referred to, as the sandstones in the lower 

 portion, though assigned by both authors to the Carboniferous,* may yet prove 

 to be Cambrian. Peale's section includes the following beds: 1. Granite; 2. Very 

 coarse white sandstone, 80 feet; 3. Red calcareous sandstone, i feet; 4. Dark 

 purplish cherty limestone, 3 feet; .5. Compact red sandstone in layers of 1 foot 

 thickness, with cross seams of calcite, 1.5 feet; 6. Red calcareous sandstone, very 

 hard and with cross cleavage layers of 1 inch, 3 feet; 7. Irregular limestone, with 

 pebbles of greenish chert and limestone, 3 feet; 8. Indistinct outcrop of limestone, 

 with chert pebbles and fossiliferous — in the upper part of the space a purplish 

 sandstone, above which is a gray sandstone passing into the next bed — 6 feet. Peale 

 says (p. 198): "The fo.ssils found in No. 8 {Terebratula and Spiriferinci) prove it to 

 be Carboniferous beyond a doubt." This stratum, which probably belongs to the 



« Found not in the Uinta Mountains proper, but south of them, in eastern Utah. 

 !)U. S. Geol. Geog. Surv. Terr., [Seventh] Ann. Kept., for 1873, 1S74, p. 197. 



