FORT UNIOX OF CRAZY MOUNTAIN FIELD, MONT. 27 



that more detailed study and discovery of fossils, especially verte- 

 brates, would permit their differentiation here. West of the moun- 

 tains the late Cretaceous and early Tertiary strata are thi'own into a 

 series of folds, rouglily parallel to the mountain flank and udth north- 

 south trend. There is no wide zone of Fort Union, as east of the 

 mountains, but strata lithologically similar to the Fort Union do occur 

 in narrow zones, as folded. Some of them are almost identical in 

 character with the Melville beds of the eastern flank and include 

 abundant leaves. This Fort Union facies, overlying the Livingston, 

 also occurs in the southern part of the mountain area, but it is much 

 disturbed and poorly exposed and not enough work has been done to 

 trace its continuity with the well-differentiated series in the north- 

 eastern area. It is probable, as Stone and Calvert suppose, that it 

 includes only the upper part of the Fort Union of the latter region. 

 No mammals have been found in it.'° There is a large area litho- 

 logically like the Melville around the southeastern flank of the 

 mountains also, but here again exact correlation is impossible at 

 present, and considerable search has not yet revealed any mammals 

 or other fossils indicative of exact age. 



The Fort Union exposures are siu-rounded by older rocks throughout 

 the northern and western areas, and no extension or correlation of 

 the beds in these directions is possible. 



Following the beds southward, the division between the No. 1 and 

 No. 2 tends to break down, and this is probably true also of that 

 between the Hell Creek, Bear, and No. 1 Fort Union near the Yellow- 

 stone River. The beds here take on a violet hue, especially the 

 shales, a color also seen in the northern area but there rare and here 

 predominant. The indivisible beds so colored apparently include the 

 Lebo, probably the lower part of the Melville, and also extend down 

 into the Cretaceous — that is, this part of the series is blending into 

 the undivided Livingston, as reported by Stone and Calvert. 



There is a dark sandstone that may represent part of the No. 1 

 Fort Union skirting this area and visible near the 4,700-foot contour 

 on the south of the divide between the Yellowstone and Stillwater 

 Rivers, south of Reed Point, and also apparently at Absarokee, but 

 the identification is uncertain. If this is the No. 1, it represents the 

 farthest point to which a definite subdivision of the Crazy Mountain 

 Fort Union can really be traced, even in this highly dubious fashion, 

 as far as I have been able to ascertain. We were unable to establish 

 any continuity with the Red Lodge or Polecat Bench areas, and 

 lithologically the beds in those areas are not comparable to those of 

 the Crazy Mountain Field, nor are similar subdivisions recognizable. 



'" About 1910 a sheep herder showed Mr. Silberling a jaw of an animal similar to Pantolambda that he said 

 was found near the head of Shields River, or between it and Potter Creek. It was impossible to obtain the 

 specimen for exact identification or to verify its reported origin. 



