124 C. W. TOMLINSON 



2,000 feet, more or less, in Utah. 1,500 feet in the Livingston quad- 

 rangle, Montana. 



2. Coarsely crystalline, very fossiliferous limestone, free from chert. M.T., 

 150 feet, Snowy Mountain section, Yellowstone Park. 



1. Very hard, cherty, black or gray limestone. Fossils few or fragmentary. 

 M.T., 175 feet, Snowy Mountain. (Members 1 and 2 of the Mississippian 

 are differentiated from Member 3 only in Yellowstone Park and vicinity.) 



DEVONIAN 



(Member 21 may prove to be of Mississippian age; Members 1 and 2 may 

 be Silurian.) 



Three Forks Formation 



(M.T., 978 feet, Blacksmith Fork) 



21 ( = Haynes's 1, 2, and 3). Thin-bedded or papery black shales, overlain 

 by yellow or reddish sandstones, sandy shales, or arenaceous limestones. 

 M.T., 197 feet, Blacksmith Fork. 



Break in Sedimentation 



20B. Blue-gray platy or nodular limestone. M.T., 361 feet, Blacksmith 

 Fork (Beds 146B-149). 



20. ( = Haynes's 4 and 5). Fissile green shale, capped by nodular gray lime- 

 stone, both very fossiliferous; the horizon of the Clymenia fauna in 

 Montana. 130 feet, Logan, Montana. M.T., of Members 19 and 20 

 together, 420 feet, Blacksmith Fork (Beds 146-146A). 



I g > (=Haynes's 6 and 7). Orange-yellow to reddish platy limestones and cal- 

 careous shales (drab to cream or yellow on fresh surfaces). 109 feet, 

 Logan (238 feet, Goose Creek Ridge). 



Upper Division of the Jefferson Dolomite 

 (M.T., 270 feet, Blacksmith Fork) 



18. Brecciated (j-inch to f-inch fragments) drab to gray-brown, massive 

 dolomite, in most places forming cliffs. M.T., 136 feet, Blacksmith Fork. 



17. Drab, yellow, and buff to dark-brown, thin-bedded limestones or dolomites, 

 locally in part shaly. M.T., 85 feet, Livingston Peak. 



16. Moderately massive dolomite, gray to brown, with rough surface. Spar- 

 ingly fossiliferous in Yellowstone Park. M.T., 40 feet, Antler Peak 

 (Iddings and Weed). 



15. White or variegated sandstone, locally represented by light-gray dolomite 

 full of coarse quartz grains, or by limestone conglomerate ( ?) (Snowy 

 Mountain). In the Teton River section, interbedded with dark-brown, 



