NO. 5 PRE-DEVONIAN PALEOZOIC FORMATIONS 287 



Feet Meters 



16. Thin-bedded, light gray to cream-colored, hard, thin- 

 bedded, fine, siliceous silt-like mud rock, with a few 

 thin layers of bluish-gray limestones containing many 

 fragments of trilobite tests 510 i554 



Strike N. and S. Dip in lower part 35° W. 



Measured 210 feet (64.0 m.) in thickness and esti- 

 mated that the upper portion was 300 feet (91.4 m.) 

 thick. 



Total Arctomys formation 725 220.9 



MIDDLE CAMBRIAN 

 Eldon Formation 



la. Thick-bedded, rough-weathering, siliceous and finely 

 arenaceous limestones in dark and light gray bands 

 100 feet (30.5 m.) or more in thickness. 

 Thickness not measured. 



At the eastern upper end of Cotton Grass and 

 Tilted Mountain Cirques, the Eldon limestones rise 

 high above the shales and limestones of the Arctomys 

 and abut against the Devonian limestones, which are 

 upturned against them in Cotton Grass Cirque and 

 downward in Tilted Mountain Cirque on the line of a 

 westward sloping fault^. (See diagrammatic out- 

 line fig. 25). 



Section on Northeast Shoulder of Fossil Mountain 



This section is 2 miles (3.2 km.) north of the Fossil Mountain 

 section proper. It is capped by dark Middle Devonian limestones 

 (Messines), which are conformably superjacent to the light gray- 

 weathering limestones of the Skoki formation. There are no traces 

 of any distinct deposit, such as the Ghost River formation or the 

 Mount Wilson quartzite above the Skoki, but there is a thin bed of 

 shale at the base of the Devonian. 



The Skoki and Sarbach formations are excellently exposed, and 

 several zones with characteristic fossils were located, the most im- 

 portant of which is the Isotcloidcs of the lower Sarbach. The lime- 

 stones are about 400 feet (121. 9 m.) thicker than 2 miles (3.2 km.) 

 south, apparently owing largely to the development of the Skoki 

 formation. 



^ Smithsonian Misc. Coll., Vol. yy, No. 2, 1925, fig. i, frontispiece; fig. 7, p. 5 ; 

 fig. 13, p. 10; and fig. 17, p. II. 



