110 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



Wyoming; (2) the Tensleep sandstone, traced as far south as the Manitou em- 

 bayment; (3) the gypsiferous red shale and sandstone of the Chugwater, which 

 represents the red beds of the Black Hills and Wyoming. The lower part of 

 the Chugwater he considers as Permian, the upper part as Triassic or Permian. 



"Henderson' in 1908 gave an account of the Permo-Triassic (?) of the foot- 

 hills formations of northern Colorado. He distinguishes the upper part of the 

 Wyoming as partly Permian. 



"' Lyki7is formation. — Conformably overlying the Lyons is a series of varie- 

 gated, mostly thin-bedded sandstones and shales, rather friable, chiefly deep red 

 in color, with thin limestone bands, the upper part usually gypsiferous. In the 

 Boulder district Fenneman names these beds the Lykins formation. It is the 

 exact equivalent of the upper Wyoming of Emmons in the Denver Basin and 

 the Chugwater of Darton in northern Colorado. In the Denver Basin monograph 

 it is given a thickness of 485 to 585 feet; Fenneman makes it 800 feet in Four-mile 

 Canyon, north of Boulder, and Darton gives it a thickness of 380 feet at Lyons 

 and 520 feet at Owl Canyon. Though it varies greatly in thickness and in strati- 

 graphic details, its general characters are constant throughout the region. As a 

 whole the formation is non-resistant, the greater part being concealed by the 

 debris in the lateral north-south valleys caused by its destruction. 



"'From Owl Canyon to the Little Thompson I have mapped as part of the 

 Lykins a more resistant sandstone, strongly cross-bedded, which forms a ridge 

 in the valley and which sometimes extends nearly to the top of the east slope of 

 the Lyons escarpment. It is difficult to distinguish from the Lyons sandstone, 

 and should perhaps be assigned to that formation, but is uniformly separated 

 from the latter everywhere north of the Little Thompson by strata lithologically 

 resembling the Lykins. In approaching Little Thompson Canyon these inter- 

 vening beds rapidly play out, bringing the sandstone which is mapped as Lykins 

 into contact with the Lyons and making the former the crest of the escarpment, 

 almost covering the latter. Thence southward it is doubtful if the two sandstones 

 can be recognized as distinct formations, and nowhere have I found a noticeable 

 unconformity. As the two sandstones after coalescing form an almost vertical 

 escarpment, if they are distinct it is practically impossible to represent the Lyons 

 on the map, yet northward they are quite distinct. The one which is mapped 

 as Lykins in the northern region passes beneath the "crinkled" sandstone of 

 Fenneman's report, which is but a few feet above the Lyons north of Boulder. 

 This problem is worthy of future investigation. 



" ' In some places certain strata of the Lykins are very massive, though soft, 

 and portions of the formation are locally calcareous, in addition to distinct 

 limestone bands. 



"'In the absence of paleontological evidence this formation has been usually 

 assigned to Triassic- Jurassic age. It seems quite likely, however, that the base 

 of the Lykins may represent Permian time, as the immediately underlying Lyons 

 is upper Carboniferous. The upper part of the Lykins is probably Triassic or 

 Jurassic, as it is overlaid by known Jurassic in northern Colorado, though it is 

 possible that part of the Jurassic and Triassic is represented by the general un- 

 conformity between the Lykins and the Morrison.' 



"Butters^ in 1913 gave a very detailed account of the ' Permo- Carboniferous' 



1 Henderson, First Annual Report Geological Survey of Colorado, p. 168, 1908. 

 " Butters, R. M., Permian or Permo-Carboniferous of the Eastern Foothills of the Rocky 

 Mountains in Colorado, Colorado Geological Survey, Bull. 5, pt. 2, p. 65, 1913- 



