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The ExpeditionYellowstone River ReturnCoal in the Bank
Pumies Stone
Building on Coal

Side View, Fort Union Formation

Millions of years of geological history are recorded in the successive layers clearly seen in this cross-section of the Fort Union Formation. Neither Lewis nor Clark saw this particular scene, which was photographed about halfway between the Yellowstone and the Missouri rivers in eastern Montana, but they certainly saw many that were similar.

--Joseph Mussulman

Pumies Stone
Building on Coal

From Discovering Lewis & Clark ®, http://www.lewis-clark.org © 1998-2014
by The Lewis and Clark Fort Mandan Foundation, Washburn, North Dakota.
Journal excerpts are from The Journals of the Lewis and Clark Expedition, edited by Gary E. Moulton
13 vols. (Lincoln: University of Nebraska Press, 1983-2001)