The color of soils
A 1911 Washington government publication by W. O. Robinson and W. J. McCaughey of the U.S. Department of Agriculture's Bureau of Soils, written as a technical study of soil colour for agricultural scientists and surveyors. The pictures are a Department of Agriculture seal with a corn plant over a plough and a plain labelled colour triangle running from white through grayish, yellowish, reddish and brownish to black, which a designer could borrow for a simple seal emblem or a tidy diagrammatic colour key.

