ORDOVICIAK SYSTEM 411 



late on the slopes of the Deadwood formation. On Dinwoody creek the 

 massive dolomite, 50 feet thick, lies on 100 feet of shaly limestone that 

 is very sandy. 



Owl CreeJc mountains. — In the eastern part of the Owl Creek uplift 

 the Bighorn limestone is ahont 40 feet thick ; in Phlox moimtain and 

 Owl Creek canyon it is over 150 feet, and near Crow creek it is alwut 100 

 feet thick. The outcrop is continuous around the liigher central area of 

 the uplift, and it extends westward along South fork of Owl creek to a 

 point 3 miles west of longitude 109°. It shows again on the slopes ad- 

 joining Crow Creek canjon and tlie upper portion of West fork of Muddy 

 creek and in Bighorn canyon. Tlie most prominent exposures are in the 

 great escarpment of Phlox mountain. It is a hard, massively hedded 

 dolomite, mostly of a light huff color, hut somewhat darker when weath- 

 ered, filled with a coarse network of irregular siliceous masses, mostly 

 from a half to 1 inch in diameter. On Aveathering, this material stands 

 out half an inch or more on the rock surface as a ragged network, the 

 purer rock between having been dissolved. This feature and the very 

 massive bedding are characteristic. In Owl Creek canyon the massive 

 limestone is overlain by 20 feet of white limestone, capped by a 20-foot 

 massive bed similar to the thick limestone below, while at the top of the 

 formation there are a few feet of sandstone and shale. In places these 

 upper beds weather to a reddish tint, strongly suggestive of the member of 

 Eichmond age which occurs in the northern portion of the Bighorn uplift. 

 The appearance of two of the most prominent outcrops in the Owl Creek 

 canyon is shown in plates 76 and 77 of my memoir on Ordovician of the 

 Northwest.® 



Fossils and age. — Fossils usually are rare in tlie Bighorn limestone, 

 consisting mostty of fragments of maclurina and corals. At one locality in 

 the Wind Eiver mountains, however, Mr Woodruff obtained an extensive 

 fauna from the basal calcareous sandstone, which was determined by Mr 

 E. 0. Ulrich as follows: Eeccpticulites oireni Hall; Streptelasma cf. pro- 

 fundum Conrad and corniculum Hall ; a ramose bryozoan resembling 

 Callopora niultitahula Ulrich; Pledamhonites scricius, var. Dahnanella 

 testudinaria, var. Strophomena, n. sp. near 8. sulcata Yern. and S. fluc- 

 tuosa Billings; Ctenodonta cf. levata Hall; Cyrtodonta cf. rotulata Ul- 

 rich; PsiJoconclia n. sp. ; ArchinacelJa cf. A. deleta Sard, and A. subro- 

 tunda Ulr. ; Protowarthia cf. cancellata Hall; Lophospira. near L. elevata 

 Ulr. ; Trochoiiema umliiJicatum Hall; Hyolithus cf. haconi Whitfield; 

 Chiton canadensis Billings ; Ortlioceras, near 0. olorus Hall and 0. nicol- 



' Loc. clt. 



