BULL. GEOL. SOC. AM. 



VOL. 32, 1920, PL. 10 



Figure 1. — The sharp Coxe of Laccolith M. 1 of Figure 4 

 View is taken looking- due north, with minette sill, number 39, in the middle foreground. 



FiGURi-; 2. — DioTAiL OF Sill ^'L.Miuai :','.) 



Showing the polygonal columns, unusual in the sills. The rock is minette. thicklv set 

 with inclusions of I'recambrian rocks. The nearest exposures of Precambrian rocks are about 

 100 miles west. 



GOLD BUTTE, SWEET GRASS HILLS, MONTANA 



