A Herd of Bisons crossing a River Bottom on the Upper Missouri, by W. J. Hays, 1862. Engraving of a painting. In crossing the richer pastures of the river bottoms the herd will sometimes form a compact mass of a mile long; sometimes it is miles in length. A single herd has been computed to contain 10,000, even 20,000, heads. The herd is generally directed on the march by the largest old bulls...but, when retreating from man, as they precipitately, smelling him at a long distance if he comes in the line of the wind, some old bulls will also guard the rear...Nothing is so terrible as a whole herd in full stampede; the very earth shakes and everything in its track is trodden to death. When a large herd in full stampede directs its charge on the line of march of the States army in crossing the plains, the great guns have been obliged to open on the head of the advancing column to turn them from their way; for, when thus rushing madly on, had there been a collision, baggage-waggons, guns, and every living or dead thing that came in their way would have been trampled. The Indians take advantage of the liability of the herd to panic to kill immense numbers...by firing the prairie at different points.... From "Illustrated London News", 1862.