Magic Pile Erected by the Assiniboins, from Travels in the Interior of North America, 1839-43
Aquatint engraving
Ackermann & Co., London
Greenslade Special Collections and Archives
Olin and Chalmers Libraries
Kenyon College

Notice how the gradation of tone from the aquatint creates the illusion of distance in the background hills and the sky. Detail is added by printing a dark layer of contour lines, with the most precision appearing in the central foreground objects.