776 INDEX TO THE STKATIGRAPHY OF NORTH AMERICA. 



Belt Mountains. Scott quotes from the first description by Grinnell and Dana 

 (1875) : • 



The Tertiary beds found here consist for the most part of homogeneous cream-colored clays, 

 so hard as to be with difi&culty cut with a knife. The beds are horizontal. * * * Some 

 bluffs were noticed where the Miocene beds attain a thickness of about 200 feet and these were 

 capped by 50 feet of the Pliocene clays, both beds containing characteristic fossUs. 



Scott infers an unconformity between the two, there being suggestions of 

 erosion in the surface of the lower and " the fossil contents of the two series of 

 strata" being "very strikingly different." 



Calkins, in an unpublished manuscript, states that the age relations of the 

 Tertiary rocks in the Philipsburg quadrangle are very imperfectly known. 



If the Eocene is represented at all, it is probably by a very thick accumulation of cemented 

 gravels observed at the east end of the Anaconda Range and by some of the andesitic and 

 rhyolitic tuffs associated with them. These rocks are considerably tilted but show far less 

 deformation and metamorphism than the pre-Tertiary rocks of the region. No fossils have yet 

 been found in them. 



See also L 12, Chapter XVII (pp. 831-832). 



L 12. BULL MOUNTAIN COAL FIELD, MONTANA. 



According to Woolsey,''" the Fort Union formation in the Bull Mountain coal 

 field (latitude 45° 30', longitude 108°) is 1,400+ feet thick and consists chiefly of 

 gray to buff sandstone, alternating with gray shale. The sandstone, though 

 extremely variable, is commonly massive and evenly distributed throughout the 

 section. Coal beds occur at intervals of about 100 feet or less and are most numerous 

 in the upper part. The base of the formation is strongly marked by contrast with 

 a band of olive-green clay shale, which belongs to the next lower formation. 



Richards®"^ and Lupton^®^ have reiaorted later on the central and eastern parts 

 of the field respectively. 



L 12. BED LODGE COAL FIELD, MONTANA. 



Woodruff ^*^ describes the Fort Union formation in the Red Lodge coal field 

 as 8,500 feet thick and as consisting of sandstone and shale, with carbonaceous 

 shale and coal at several horizons. Workable coal beds are confined to a zone 

 above the middle of the section. The formation is therefore divided into : 



Feet. 



Upper barren member 1,975 



Middle productive member 825 



Lower barren member 5,700 



8,500 



The lowest member is composed mostly of yellowish sandstone and shale. Beguming 

 1,650 feet above the bottom of the formation is a group of beds 1,000 feet thick, composed of 

 varicolored sandy shale with a few beds of soft yellowish sandstone, numerous beds of carbon- 

 aceous shale, and in the upper part a few coal beds, one of which contains 18 to 24 inches of 

 coal. Above this group carbonaceous shale and coal beds occur at diminishing intervals as the 

 productive member is approached. * * * 



In the middle productive member * * * the sandstone and shale resemble the sand- 

 stone and shale of the lower member and do not seem to indicate any essential difference ia 



