THE LOMBARD OVERTHRUST AND RELATED FEATURES 283 



West of the overthrust fault there is another valley formed in 

 the Three Forks formation. Numerous good sections of the forma- 

 tion were obtained in the small tributary gullies which cut across 

 the dip of the strata on the western sides of these valleys. 



The fossiliferous members of the formation are Nos. 1, 2, 4, 

 and 5. The general conclusions from a study of the fauna are that 

 the formation is very late Devonian in age, as reported by Dr. 



Fig. 9. — View north from southern end of valley, at apex of southward pitching 

 anticline. 



Raymond in 1907, 1 and probably represents a transition into the 

 Mississippian in its upper part in members 1 and 2. 



Carboniferous. — Throughout the mountainous part of south- 

 western Montana the Carboniferous formations are very prominent 

 and form conspicuous and precipitous cliffs. In the region about 

 Three Forks the Carboniferous strata attain a thickness of from 

 1,500 to 2,000 feet. 



1 P. E. Raymond, Amer. Joiir. Sci., XXIII (1907). 



