This report to the state of Massachusetts was Edward Hitchcock's major work on the fossil footprints and other impressions in the sandstone of the Connecticut River Valley, the culmination of half a lifetime of labor. It is one of the first American books to use photographs for scientific illustration, although they were not printed directly onto the pages. Hitchcock used a type of photograph called "ambrotypes", which were images on glass plates. The printer used the ambrotypes as the basis for "sketches" to transfer the images onto paper.