416 N. H. DARTON PALEOZOIC AND MESOZOIC OF WYOMING 



North Platte hadn and southivanJ. — The uppermost member of the 

 Casper formation in Natrona and Converse counties and southward is a 

 hard, massive sandstone, often 100 feet or more thick, which is believed 

 to be an extension of the TensIeejD. It is conspicuous at the east end and 

 along the south side of Casper mountain and from the head of Muddy 

 creek eastward, notably on La Prele creek, where it constitutes the nat- 

 ural bridge, and on Wagonhound creek 10 miles south by west of Douglas. 

 South of ]\rarshall it is 100 feet thick and rises in high knobs, and its 

 outcrop is wide in the anticline 12 to 15 miles southwest of Garrett. It 

 constitutes "Flat Top," a high ridge on the axis of the anticline 6 miles 

 north of Medicine Bow. It is from 100 to 150 feet thick along the east 

 side of Shirley hills, from Troublesome creek to the head of IMuddy creek, 

 and appears extensively in the anticline north and west of Difficulty as 

 well as in two anticlines east of that place. The sandstone is about ,150 

 feet thick in the canyon of Platte river, 5 miles above Alcova, and it is 

 brought up again by a beautiful anticline through which the river cuts a 

 gorge just above Alcova (see plate 24). 



Age. — ISTo fossils were observed in the Tensleep sandstone in central 

 "Wyoming, but in the Bighorn mountains it contains a Penns3dvanian 

 fauna. 



EMBAR FORMATION 



General relations. — In the Owl Creek and Wind River uplifts and for 

 some distance southeast the Tensleep sandstone is separated from the 

 Chugwater red beds by a series of limestones and cherty beds from 150 to 

 250 feet thick, which has been designated the Embar formation. It ap- 

 pears not to extend into the Platte Eiver region, excepting one or two 

 doubtful occurrences. 



Owl CreeTc tiplift. — In the Owl Creek uplift the Embar formation 

 varies from 200 to 250 feet thick. It outcrops along both sides of the 

 Owl Creek mountains and the north side and east end of the Bridger 

 range. The most prominent exposure is in the great dip slope adjoining 

 Bighorn canyon, a few miles south of Thermopolis, where an upper lime- 

 stone 50 feet thick constitutes the surface for many square miles. The 

 formation is also extensively exhibited along the mountain slopes near 

 the head of Muddy creek, along the line of outcrop extending through 

 Anchor, and in the anticline southeast of Embar. It appears again in 

 the more elevated portion of the anticline which passes through Ther- 

 mopolis. The limestone in the canyon walls south of Thermopolis is 50 

 feet thick, of gray color, moderately massive bedding, and of considerable 

 hardness. It is underlain by about 100 feet of shale, partly limy, filled 

 with oval concretions of chert mostlv from 1 to 2 inches in diameter. 



