DENISON OLMSTED AND THE 1825 GEOLOGIC MAP OF NORTH CAROLINA

Early geological mapping in the United States was often on a small scale. Not until the early 1800’s was knowledge of the regional geology sufficient for the first geologic map by McClure (1808). His map was a broad-brush representation of geologic knowledge gleaned from his own travels and observations, as well as numerous other investigators. The description of the units was based upon Wernerian stratigraphy, modified by McClure (1808) to relate to the descriptions and outcrops found from the northeastern states to the Gulf of Mexico. McClure’s 1817 revision further modified the Wernerian stratigraphy, indicating influence by the work of early geological investigators such as Benjamin Silliman.

In 1823, the North Carolina General Assembly authorized a geological survey, hiring UNC-Chapel Hill mineralogy professor Denison Olmsted. Olmsted was charged to “promote agriculture and family manufactures within this state” and to “direct his attention chiefly to such objects as were of practical utility.” With these demands in mind, the “Olmsted Survey” began the first geological survey of North Carolina, even though he was not designated as the official state geologist.

The draft geological map produced by Olmsted in November 1825 was never published. Titled “Geological Map of North Carolina,” it is small (10 x 15.25”) and was created prior to Olmsted’s departure to his new position at Yale. Although the map was catalogued in Laney and Wood (1909) and mentioned in Merrill (1924), it was thought lost, until a chance rediscovery of it in a map drawer in the North Carolina Geological Survey map collection.

Examination of the geologic map reveals that it was probably used in conjunction with Olmsted’s preparation of his 1825 reports. The units described by Olmsted were a modified form of the Wernerian stratigraphic column, similar to McClure’s (1817) map. In addition, the map reveals how Olmsted followed his interpretation of the legislature’s demand to provide a practical venue for agricultural and economic mineral resources rather than examining the geological structure and rock relationships of the region. This is especially apparent in the detailed depiction of the coastal inlets, as Olmsted was attempting to show that the geological survey was providing useful information for the improvement of “internal navigation”.