302 



W. II. WEED — TWO MONTANA COAL FIELDS. 



mences to cut through the nearly horizontal strata of the plains, and 

 near Great Falls plunges over a series of sandstone ledges in a succes- 

 sion of cataracts collectively known as the " Great falls of the Missouri.'' 

 Below the falls the sandstones gradually pass beneath the dark carbona- 

 ceous shales so well exposed at Fort Benton, from which place they take 

 their name. These sandstones, with their interbedded shales, now known 

 as the Great Falls formation, have long been known to all geologists visit- 

 ing the region, but until recently failed to reveal any fossil remains and 

 were referred to the Dakota epoch, whenever mentioned, on account of 

 their inferior position to the well developed Fort Benton shales. Their 

 true age was first made known by Professor J. S. Newberry,* who identi- 

 fied a number of fossil plants from the Great Falls formation and found 



Figure 1. — Sketch Map of Montana showing Location of Coal Fields. 



The shaded zone extending from the headwaters of Musselshell river to the hit irnational 

 boundary includes the coal fields. 



them to be species characteristic of the Kootanie rocks of the Canadian 

 geologists. 



South of Great Falls, a few miles nearer the mountains, this formation 

 holds a thick seam of excellent bituminous coal, which is being exten- 

 sively mined at Sandcoulee and has been opened at a number of other 

 localities along the base of the mountains. The area underlain by coal 

 has been called the Great Falls coal field, and as these strata constitute 

 the only occurrence of the Kootanie rocks yet recognized in our territory 

 they possess a decided interest apart from their economic importance. 



In prosecuting a study of the coal fields of Montana for the United 

 States Geological Survey, a visit was made to this held in the spring of 



♦ School of Mines Quarterly, vol. viii, no. 4, July, 18S7, p. 327. 



