208 C. D. WALCOTT PRE-CAMBRIAN FOSSILIFEROUS FORMATIONS 



Belt terrane. The estimated thickness of the formation in the type 

 locality is 300 feet. 



The only section of the Belt terrane measured in detail is that studied 

 b}^ Mr Weed on Belt creek, near Neihart. It is less than half the thick- 

 ness of the section in the Big Belt mountains and westAvard to Helena. 

 The formation names have been inserted in Mr Weed's section as nearly 

 as I could determine the horizons by comparison with other sections. . 



Section of the Belt terrane.- — -This section, which is exposed on Belt creek, 

 south of Neihart, Montana, and from which the measurements were made, 

 is as follows : 



Cambrian: Feet Feet 



Cambrian sandstone, dark red, containing white pebbles with 

 quite ferruginous matrix ; only 40 feet exposed, the bed occur- 

 ring in the creek channel a quarter of a mile below the forks 

 of the stream 100 



100 



Plane of unconformity. 



Spokane shalks : 



Red shales 200 



Red shales — laminated, brittle, and quite hard 10 



210 



Greyson shalks: 



Shales general) j' gray, rarely exposed, and forming densely 



wooded slopes 700 



Gray sericitic shale, locally disturbed by a horizontal sheet of 

 minette 170 



Shales exposed in wall on west side of canyon ; thinly bedded 

 slaty shales carrying limestone and fossils in the shaly slates, 

 2 miles to the southeast' 60 



No exposure 25 



955 



Newland lijiestone: 



Massive, block-jointed limestones, blue on fresh fracture and 



weathering an earthy brown ; dip, 20 degrees south 15 



Calcareous shales and thinly bedded limestone; beds hidden 



by talus 200 



Limestones with massive outcrop, blue on fresh fracture, weath- 

 ering an earthy buff color 60 



Slates (minette intrusion) 125 



Limestone, fissile and slaty 18 



Massively bedded slate 15 



Impure limestone 5 



Black or gray slate with glistening surface ; dip, 30 degrees. ... 15 

 Trachyte intrusion, which disturbs normal dip of strata. 



Limestone and slate, not well exposed. . . 30 



Minette sheet 6 



