The Hitchcock family’s interest in geology passed from Edward to his son Charles, who by 1861 was appointed the State Geologist in Maine, and later in the decade State Geologist in New Hampshire. Geologic mapping of the area west of the Mississippi River grew rapidly after the Civil War, and the 1872 map displayed here by Hitchcock and William Blake is an example of that effort. Prepared for the 1870 statistical atlas of the United States, this map represents a transition from earlier 19th-century examples, as it uses highly detailed placement of vivid colors to differentiate between geologic time periods, and examines the fossils contained within the rocks.