FORT UNION OF CRAZY MOUNTAIN FIELD, MONT. 23 



under the influence of the Widdecombe Creek antichne, the axis of 

 which is mostly on the lower Lebo, with the upper Lebo forming a 

 horseshoe valley around it, the eastern limb being occupied b}^ Widde- 

 combe Creek. The exposures then swing around the northern end of 

 Bear Butte (with the No. 2 also continuous through the gaps across 

 the axis of the Bear Butte syncline) and then swing southward and 

 widen until they form a very wide area of low relief in the vicinity of 

 the Glass Lindsay lakes (Lake Adam and Lake Walvoord). The upper 

 limit against the No. 3 swdngs abruptly westward in sec. 34, T. 4 N., 

 R. 15 E., and runs over to the Crazy Mountains, which it reaches 

 some 17 or 18 miles south of its northern departure from those moun- 

 tains. The exposure as a whole thus forms a great loop closed on the 

 west by the mountains, as shown in plate 1. 



The No. 1 and No. 2 beds seem to be perfectly conformable and to 

 intergrade, forming a natural unit, sandier in its lower part, so that 

 the single name Lebo for both is acceptable. In the northern part of 

 the field they are generally sharply separable, but in the south it is 

 often difficult to distinguish them. It is to be noted, however, that in 

 this southern area they are nearly horizontal and are very poorly 

 exposed and that in this direction all subdivisions, even between 

 undoubted Cretaceous and Tertiary, tend to break down or to be 

 very difficult to distinguish. 



The best exposed section shoAving the whole thickness of the Lebo 

 is in sees. 15-22,^ R. 6 N., T. 15 E., where it has been measured by 

 Stanton and Silberling who give the following section (Stanton, 1909, 

 p. 263, here slightly modified): 



No. 3 { Massive sandstone (Not measured) 



Feet 



Shale with a few thin bands of sandstone 112 



Gray sandstone 5 



Shale 18 



Gray limestone, weathering brown [a concretionary layer, not a 

 No. 2^ continuous stratum] 3 



Greenish-gray somber shale with much soft sandstone of same 

 color and brown .... concretions in lower third, a few thin 

 bands of sandstone in upper part and several concretionary 



. zones near top 700 



No. 1 



838 



(Brown, thinly cross-bedded sandstone forming .... ridge 32 



[Somber greenish] shale 200 



Greenish-gray sandstone 15 



Greenish-gray ehale 249 



496 



A section of the underlying beds at this same locality is given on a 

 previous page. 



> Stanton says sec. 15, but the greater part of the beds are here in the adjacent sec. 22. 

 119212—37 3 



