Columbia subject headings:
Geology--Montana.
Ludlow, William, 1843-1901.
Montana--Description and travel.
Paleontology--Montana.
United States--Discovery and exploration.
Yellowstone National Park.
Zoology--Montana.
Harvard subject headings:
Princeton subject headings:
Geology--Montana.
Ludlow, William, 1843-1901.
Montana--Description and travel.
Paleontology--Montana.
United States--Exploring expeditions.
Yellowstone National Park.
Zoology--Montana.