CAMBRIAN AND LOWER ORDOVICIAN. 117 



The hard sandstone at the base of the sedimentary series in the Casper Range and in the 

 ridges to the southeast appears to be a shore deposit of the Casper formation. 



Battlesnake Mountains. — ^The Deadwood formation outcrops along a portion of the crest 

 of Rattlesnake Mountains west of Oil City. It is about 800 feet thick. At the base and near 

 the middle are 25 to 40 feet of brown to buff fossiliferous sandstone and the basal beds are 

 somewhat quartzitic. Sandy gray shale with thin gray sandstone layers constitute the greater 

 part of the formation, but there is a small amount of impure slabby limestone and reddish 

 shale near the top. Glauconite is a conspicuous ingredient in most beds. 



Wind River Mountains. — On the northeast slope of Wind River Mountains the Deadwood 

 formation is, about 750 feet thick, and it presents all the features which are characteristic in 

 the Bighorn and other ranges northeastward. Its presence was recognized by Comstock and 

 its distribution was shown in part on maps of the Hayden Survey. 



The basal member, which lies on granite, is about 100 feet thick and is the usual hard 

 brownish sandstone. Next are sandy shales and slabby limestone, the latter including more 

 or less of the typical flat-pebble conglomerate of gray Umestone pebbles covered with glauconite. 

 The top layer of this limestone contains many trilobites. At the top of the formation is a 

 hard, coarse, fossiliferous sandstone. 



Owl Creek Mountain^. — Extensive exposures of the Deadwood formation extend along the 

 upper slopes of Owl Creek Mountains and in the canyon of Bighorn River. It also appears 

 along Crow Creek northeast of Circle and in Owl Creek canyon. The thickness is 900 feet and 

 the succession of rocks is similar to that in the Bighorn and Wind River mountains. At the 

 base is hard coarse-grained reddish-brown sandstone, locally conglomeratic below and lying on 

 a remarkably smooth plain of the pre-Cambrian rocks. It varies from 50 to 100 feet in 

 thickness and is succeeded by 200 to 300 feet of sandy shales and thin-bedded sandstones, 

 with a prominent bed of sandstone in their lower portion. In Bighorn Canyon this bed is 50 

 to 60 feet thick and of bright reddish brown color. The medial member is 400 feet or more 

 of soft greenish-gray shale with a conspicuous gray to buff limestone in its lower part. This 

 limestone, usually 50 feet thick, consists partly of flat pebble limestone conglomerate. South- 

 west of Embar it is 30 feet thick and 300 feet above the base of the formation. At the head of 

 Muddy Creek it is 40 feet thick and underlain by a somewhat thicker mass of sediments. The 

 top member of the formation is slabby Hght colored limestone over 100 feet thick at most 

 localities, but apparently either very thin or absent in Owl Creek canyon. It contains frequent 

 layers and masses of the characteristic intraformational conglomerate of flat limestone pebbles 

 more or less intermingled with thin, twisted, and broken layers of limestone in a matrix of 

 shale and fine limestone sand. Many of the pebbles are so thickly covered with grains of 

 glauconite that they appear to be green, but inside they are gray or pinkish, similar to the 

 associated beds. 



Fossils. — ^Fossils at various horizons in the Deadwood formation are of middle Cambrian 

 age, and Dicelamus politus and Ptychoparia oweni are the principal forms. The former is a 

 small oval shell, which occurs in great abundance in the middle sandstones and in the limestone 

 layers in the shales, as well as in the upper limestone series. The Ptychoparia is a trilobite 

 which often abounds in the basal sandstone. In the middle sandstone of the formation, a 

 short distance west of Garfield Peak of Rattlesnake Mountains, the fossils included a new 

 species, which Mr. Walcott has designated Oholus (Westonia) dartoni. In the top sandstone 

 west of Lander, Orthis (Plectorthis) [EoortJiis] wichitaensis was found. 



Blackwelder, in an unpublished manuscript (1910), says: 



The Deadwood formation of central Wyoming expands westward without suffering much 

 change in Hthologic character. Near the south end of the Teton Range the basal sandstone 

 is still only 160 feet thick, but it is overlain by fossihferous shales and striped limestones, 

 which are locally conglomeratic and oohtic, to a thickness of 1,000 to 1,100 feet. The supposed 

 Cambrian beds are not sharply separated from the overlying massive limestones which contaia 

 Ordovician and Silurian fossils. 



