EASTERN COLORADO 



561 



Geologic Section of Fremont Limestone and Harding Sandstone near Hard- 

 ing's Quarry, northwest of Canyon City, Colorado 



Fremont limestone: Feet 



Compact, hard, light-gray limestone, breaking into angular frag- 

 ments, but with a band of purple and gray calcareo-arenaceous 



shale at the base, containing a large Trenton fauna 45 



Dark, reddish-brown sandstone 10 



Hard, compact, light colored limestone, with fossils 45 



Gray, silicious, magnesian limestone, somewhat ferruginous in lower 

 portion ; weathers locally to reddish friable rock, except that near 

 base limestone weathers into rough irregular cliffs with many 



caverns and holes ; corals and other fossils 170 



Red and purple fine grained, argillaceous, arenaceous shale; fish- 

 plate fragments (see plate 79) 2-A. 



Harding sandstone: 



Coarse purplish sandstone in several layers with gray layers above. 11 



Gray and buff sandstone 7 



Fine grained, argillaceous, arenaceous shale 3 



Massive gray and reddish sandstone with thin, irregular beds of 

 reddish-brown, sandy shale in lower portion ; numerous fish re- 

 mains . 20 



Reddish-brown, sandy shales, partly calcareous in some layers ; fish 



plates and other fossils abundant 7 



Compact, thinly bedded, reddish and gray sandstone passing into a 

 gray and more massively bedded, somewhat friable, sandstone 

 that changes at 25 feet up into a purplish tinted, somewhat coarse, 



friable sandstone ; dip 40 degrees 33 



Coarse, light-gray sandstone 5 



Granite. 



Overlying the Fremont limestone are 15 to 30 feet of impure variegated, 

 banded limestones, with interbedded sandstones and argillaceous beds 

 containing Mississippian fossils. The unconformity between the two 

 limestones — a hiatus representing Silurian and Devonian time — is not 

 marked by discordance of dip nor by any noticeable erosion features. On 

 the north side of Arkansas river, at the mouth of the Eoyal gorge, the 

 Ordovician beds are well exposed, lying on granite and gneiss and dipping 

 steeply eastward. There is a basal conglomerate merging upward into 

 hard gray to pink sandstones, in part coarse grained, 100 feet or more in 

 thickness. These are succeeded by 80 feet of reddish-brown shales and 

 thinly bedded sandstones, 70 feet of gray to pink sandstones (mostly soft 

 and massive), 8 feet of red shales, 30 feet of gray to pink sandstones 

 (mostly massive), followed by a talus-covered interval of about 100 feet, 

 east of which appear ledges of Fremont limestone merging upward into 

 a few feet of gray sandstone. The latter is overlain by the basal red con- 



