Abstract

Glacial striae on shonkinite exposures at Snake Butte, a prominent intrusive in the plains south of Harlem, Montana, trend southeastward. A train of shonkinite boulders, many of them enormous and some of them striated and polished, extends southeastward 50 miles from Snake Butte across the plains of the Fort Belknap Indian Reservation. The indicated southeastward movement of the ice is explained as a diversion of the southward-moving Keewatin glacier as it piled against the north side of the Bearpaw Mountains, developing a downward gradient toward the southeast.

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