NO. 5 PRE-DEVONIAN PALEOZOIC FORMATIONS 285 



From the strike and dip, it is estimated that there may 

 be 200 to 300 feet (60.9 to 91.4 m.) in thickness 

 beneath the lowest beds of the Mons as exposed east 

 of Fossil Mountain and the Upper Cambrian Sabine 

 formation. This would give 875 to 975 feet (266.7 to 

 297.2 m.) in thickness for the Mons, or about 100 feet 

 (30.5 m.) greater than is found 4 miles (6.4 km.) to 

 the eastward in the Bonnet Peak section. 



In the lower part of the Mons, a species of Sym- 

 physiirina occurs in a layer of limestone that projects 

 from a debris-covered slope 500 feet (152.4 m.) or 

 more west of the Lyell limestone at the west foot of 

 Cotton Grass Cirque. 



UPPER CAMBRIAN 



The uppermost Cambrian beds, if present in this section, are con- 

 cealed by debris and drift deposits, but on the strike one mile (1.6 km.) 

 to the south, they are finely exposed on Tilted Mountain Brook, where 

 the boundary between them and the superjacent Mons may be seen 

 below the foot of the falls where the brook enters the canyon valley 

 of Baker Creek. 



The thick-bedded, hard, light gray and coarse magnesian limestones 

 of the Lyell formation form the western side of the high, long ridge 

 of which Oyster Peak on the north and Tilted Mountain on the south 

 are points rising above its average height. This ridge is on the eastern 

 side of the Upper Red Deer-Baker Lake Canyon Valley, of which 

 Fossil and Brachiopod Mountains form the western limits, except 

 where the broad east and west Baker Lake depression comes in be- 

 tween them. A mile (1.6 km.) south of the summit of Oyster Peak 

 and again at the north base of Tilted Mountain, a large, deep glacial 

 cirque has cut back into the ridge exposing sections of the Upper 

 Cambrian formations. For the Oyster Peak Ridge cirque I am pro- 

 posing the name Cotton Grass, and for the Tilted Mountain cirque, 

 Tilted Mountain. These cirques are illustrated on plates 50 to 55. 

 The section at Tilted Mountain Cirque is about the same as that of 

 Cotton Grass Cirque. 



Lyell Formation 



Feet Mete 



The section exposed below the Mons is shown in 

 a few small outcrops of shale and an occasional thick 

 layer of gray pebble or interformational conglomerate 

 limestone,^ and beneath the latter the thick layers of 

 the Lyell limestone form the slope up to the mouth 

 of the cirque. 



^ The pebbles or nodules in these liinestones appear to have been formed of 

 rolled pieces of calcareous mud of about the same character as their matrix. 

 They often contain bits of fossils similar to those in the matrix. 



