282 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



the Devonian limestones ; the latter have been crushed together on 

 the north and south axis of the mountain so as to form a rather sharp 

 syncline at the summit (see pi. 48). On the east face the bedding and 

 dip are uniform down to the shaly beds of the Mons formation, in 

 which the broad canyon valley between Fossil Mountain and Oyster 

 Peak has been eroded (see pi. 48). The western side of Oysier Peak, 

 as well as its southern ridge, is formed of the hard, compact, thick- 

 bedded, gray arenaceous and magnesian limestones of the upper part 

 of the Lyell formation. On Oyster Mountain, directly east of the 

 summit of Fossil Mountain, a great glacial cirque extends back for 

 nearly a mile (1.6 km.) into the ridge, exposing the Upper Cambrian 

 Lyell formation, some of the Bosworth and Arctomys, and the Middle 

 Cambrian Eldon formation. A fault here interrupts the section 

 in about the same manner as in the Ranger Brook section, 19.5 miles 

 (31.4 km.) to the southeast. 



From the summit of Fossil Mountain down the eastern side there 

 is an estimated thickness of 600 feet (182.9 rn.) of thick-bedded, dark 

 gray, rough-weathering Devonian limestones that correspond in ap- 

 pearance and in the presence of Middle Devonian corals to the Mes- 

 sines formation of the Clearwater section 16.5 miles (26.5 km.) to the 

 north-northwest. 



The presence of Devonian corals and stromatoporids in abundance 

 in the talus of the south side of Fossil A^ountain, undoubtedly sug- 

 gested its name. 



DEVONIAN 



DiSCONFORMITY 



Feet Meters 



No apparent physical unconformity exists between 

 the rough-weathering, dark lead-gray limestones car- 

 rying numerous corals and stromatoporids of the 

 Middle Devonian Messines formation and the sub- 

 jacent strata. 



Ghost River Formation? 



Beneath the Devonian there is a series of thin layers of 

 magnesian limestone with layers of chert i to 2 inches 

 (2.5 to 5.0 cm.) thick which may be between the 



layers or form part of them 35 



The dark, coarse Devonian Messines limestone 

 above and the light gray relatively soft Ordovician 

 Sarbach limestone beneath these cherty magnesian 

 beds define the latter as a formation unlike either, and 

 as one deposited under dissimilar conditions. It may be 

 the representative of the Ghost River formation of 

 the Ghost River section (p. 261). , 



