INTRODUCTION 439 



international boundary. All three rise abruptly from the plains at a 

 distance of approximately 100 miles east of the Rocky Mountains. The 

 summits at the maximum are nearly 3,000 feet above the neighboring 

 jjlains and are striking landmarks, even when viewed from the railway 

 train at a distance of 40 or 50 miles. As a result of observations made 

 ill 1873-74, Dr. George M. Dawson^ records that these isolated moun- 

 tains were called by the half-breed hunters "Montagues du Foin de 

 Henteur," and by the traders of the Missouri region the "Sweet Grass 

 Hills." On the maps of that time they were also named "Three Buttes.'' 

 Today the name Sweet Grass Hills seems well established and in general 

 usage. 



The three elevations are called, from east to west. East Butte, Middle 

 Butte, and West Butte. The center of the Middle Butte uplift is distant 

 10 miles from the center of West Butte and practically the same from 

 the center of East Butte. The area of uplift for East Butte is, roughly, 

 9 miles from east to west and 10 miles from north to south. Middle 

 Butte is smaller. Its uplift extends about 5 miles from east to west and 

 the same distance from north to south. West Butte covers an area, 

 roughly, 5 miles east and west by 6 miles north and south. The relative 

 positions are shown on figure 1. West Butte is some 20 miles east from 

 the toAvn of Sweet Grass, on the branch of the Great Northern Railroad, 

 which connects the main line with the Canadian railway leading north 

 into Alberta. The town is at the international boundary. The main 

 line of the Great Northern is somewhat farther south of the hills. A 

 mail auto-service runs daily from the post-office of Gold Butte, on the 

 western side of Middle Butte, southeast 28 miles, to Chester, on the main 

 line of the Great Northern. As stated above, the Rocky Mountains are, 

 roughly, 100 miles to the west. The Bear Paw Mountains, an eroded 

 volcanic center, are nearly 100 miles southeast. To the south the High- 

 woods, embracing both volcanic plugs and laccoliths near Great Falls, 

 are over 130 miles distant. To the north, in Alberta, there are moderate 

 elevations of sedimentary strata in the Evergreen Hills, which can be 

 seen from the Sweet Grass Hills on the farthest horizon. In the great 

 plains there are no more outbreaks of igneous rocks to the north and east 

 for hundreds of miles. 



The Sweet Grass Hills are thus the most northerly of the laccolithic 

 and volcanic mountains lying east of the main range of the Rocky Moun- 

 tains in Montana, and of which the very valuable papers of Waldemar 



2 British North American Boundary Commission. Report on the geology and resources 

 of the region in the vicinity of the forty-ninth parallel. Montreal, 1875, p. liiS. 



XXXI — Bull. Geol. Soc. Am., Vol. 32, 1920 



