Outer (Jlacial Drift. — Uphaui. 153 
sonu' looalitics, lia\'f Ijccii niaik', l)y L'1iaml)viiin and Salisbury 
in central Montana; \)\ (."nlvcr on the front rang-:! of the Rocky 
mountains in the north cdme of that state; by Weed in the 
vicinity of h'ort lienton ; and hv Chaniberhn, Wilhs, Russell, 
and others, in Idaho and Washing^ton. 
There yet remains, however, to he applied to all that west- 
ern half or two-fifths of our continental drift border, from 
western North Dakota and tlu' lower Yellowstone river to 
Puget sound and the ( )lyni])ian mountains in Washington, 
the painstaking diflferentiation of the successive stages of the 
Glacial period, and precise mapping of any marginal moraines 
that may be found, such as have been very carefully and in- 
structively worked out in the northern central states of the 
Mississippi basin, from Ohio to Iowa and Minnesota, noting 
there a dozen or more moraine-forming stages in the departure 
of the ice-sheet. 
Broadly viewed, the most noteworthy feature of the western 
half of the continental drift sheet is its less extent southward 
than that of its eastern half, from Kansas to the Atlantic 
coast. The rather arid climate of the Great Plains from the 
lower [Missouri river to the Rocky mountains, and likewise 
of the wide Cordilleran belt until we come to the narrow tract 
between the Cascatle range and the Pacific, had the efifect 
to limit the glaciation in Montana and westward to latitudes 
averaging about eight degrees, or 550 miles, north of the 
average limit from Kansas eastward. 
In the central part of the continent, for the distance of 
about 1.600 miles, from southwestern Ohio to the upper Mis- 
souri river and its trilnitaries. Maria's, Teton, and Sun rivers, 
in northern Montana, reaching nearly to the base of tlie Rocky 
mountains on the international boundary, the border of the 
glacial drift belongs to earlier stages of the Ice age than either 
east or west. Through that central region, the outermost 
drift, referred to the Albertan. Kansan Illinoian. and lowan 
stages of the long (ilacial period, has generally, an attenuated 
edge, destitute of morainic knolls, hills, and ridges, such as 
extend in narrow belts along the boundaries of the late Wis- 
consin drift, and which also, in a numerous series of these mo- 
rainic belts, traverse the areas of that later drift, marking 
pauses or slight re-advances during the general retreat of 
