Outer Glacial Drift. — L'pluuii. 157 
i'mk'ssnr (I. I^. Culver, cxplorini;' tlic fr«iiit ranj^c of the 
Rockies in northern ]\fontana. found that ice was accumulated 
so thickly west of the main eastern range, within thirty miles 
southward from the forty-ninth parallel, that it outflowed 
eastward through th.c passes, carrying dioryte boulders from 
ledges west of the watershed to a distance of several miles on 
the plains at the eastern base of the mountains. No Laurentide 
cr eastern drift was observed there, but in the valley at the 
head of St. Mary's river, a tributary of the Belly river, flow- 
ing northeastward into Alberta, on latitude 113° 30", five to 
twenty miles south of the international boundary, he noted 
shore lines of a glacial lake, which was probably formed by 
the neighboring barrier of the Laurentide ice-sheet on the 
northeast. These old shore lines occur up to tlie higl:t of at 
least 800 feet above the present St. ^Mary's lakes, or approx- 
imately 5,400 feet above the sea.'^' 
Tlie Altamont, Gary, Antelope, Kiester, Elysian, Waconia, 
and later moraines, which have been traced in concentrically 
lobate courses through South and Xor*-h Dakota,! were quite 
surely formed at exactly or approximately the same time with 
the terminal moraines, outermost and recessional, which cross 
Ohio, southwestern Xew York, Pennsylvania, Xew Jersey, 
Long Island, and southern Xew England. Throughout that 
eastern part of their extent, the outer moraine is at or near 
the extreme boundary of the glacial drift. In -ill the interior 
region, however, from Ohio to the Rocky mountains, the out- 
ermost of this series of moraines lies far back from the drift 
boundary, excepting on the east side of the Wisconsin drift- 
less area, and again along a considerable distance, about 200 
miles, in South Dakota, where the Altamont moraine comes 
nearly or quite to the Missouri river, while the older glacial 
drift beyond this moraine is scanty or altogether wanting west 
of the river. 
It also appears very certain, according to the judgment of 
expert glacialists, that the latest great development of glaciers 
and piedmont ice-sheets in the western Cordilleran region 
of the L'nited States, spreading generally farther than in the 
• 
'Trans.. Wisconsin Acndemv of Scieace. Arta and Letters, vol. viii. pp. 
187-205, with map; Dec. 30, ISOl. 
Tj. 1-: Todd. Proc. .\ . .\. A. S.. vol. xxxiii. 18S+. pp. 381-.S93; V. S. Geol. 
Survey. Bulletin No. 1++. 1&9C.. 69 pages. \\ akhek Vrii AM, V. S. Geol. Stir- 
vey, Slon. XXV, 1895, chapter iv, pp 108-l"91. 
