2'/2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



Bonnet Peak Section 



This section is at the head of Lake Douglas Canyon Valley in the 

 northwestern portion of the Sawback Range, 15 miles (24 km.) north- 

 northwest of Ranger Canyon section and nearly 6.7 miles (10.8 km.) 

 east-southeast of Fossil Mountain section. The dark massive beds of 

 Middle Devonian Messines limestones f-orm great northward-facing 

 cliffs overlooking the upper alpine valley of Douglas Creek, 6 miles 

 (9.7 km.) south of Lake Douglas and about 1.5 miles (2.4 km.) north 

 of Bonnet Peak (10,615 feet, 3,235-5 "i)- (^ee pi. 35-) The high 

 cliffs extend west and north on the western side of Douglas Canyon 

 Valley until they merge into the cliff slopes of Mounts St. Bride 

 (11,220 feet, 3,419.9 m.) and Douglas (11,015 feet, 3-3574 m)- 

 (See pi. 37.) 



The Ghost River formation, which appears to be represented at 

 Fossil Mountain section by 35 feet (10.7 m.) of cherty magnesian 

 limestone, is represented by not more than 10 feet (3 m.) of a drab, 

 buff-weathering, finely arenaceous shale. This shale readily breaks 

 down and disintegrates to form a well-defined zone at the base of the 

 Devonian cliffs. The conditions here are similar to those in the Ranger 

 Canyon section where a thin bed of shale is all that occurs between the 

 Devonian and the subjacent Sarbach formation. There is no evidence 

 of an unconformity between the Devonian and Sarbach at either 

 locality. 



DlSCONFORMITY 



DEVONIAN 

 CANADIAN 



Sarbach Formation 



The only recognizable beds that can be referred 

 to the Sarbach formation are layers of cherty lime- 

 stones beneath the Devonian shale, which are similar 

 to a series of beds above the Mons formation as it 

 occurs 15 miles (24.1 km) to the south-soutlicast in 

 the Ranger Canyon section (see p. 264). These lime- 

 stones break down and form a broad, irregular, rough 

 slope towards the clififs above Lake Gwendolyn. The 

 section was measured across this slope and down to the 

 lake and across the brook to the slope leading to the 

 amphitheater beneath and west of Halsted Pass, where 

 the upper beds of the Upper Cambrian Lyell forma- 

 tion are exposed. 



Only a few fossils were collected as none of them 

 was striking or well preserved. The entire thickness 

 of the Sarbach was found to be about 520 feet 



