A glowing exception to the perceived absence of twentieth-century woman geographers and cartographers is the monumental work of Marie Tharp. Her large collection of material which comprises some of the finest work ever produced by a woman cartographer is held by the Geography and Map Division. The Heezen-Tharp Collection, dating from the 1940s to the present, is based on the work of Bruce C. Heezen and Marie Tharp who were pioneers in the exploration and mapping of the ocean floors.

Marie Tharp and Bruce Heezen's work proved that the ocean's Atlantic Ridge extended into the Arctic, went around the tips of both Africa and South America, and joined with similar structures in the Indian and Pacific Oceans, confirming that the Atlantic Ridge is part of a continuous set of ridges existing at the Earth's plate boundaries for over forty thousand miles. The geographers' work supported and confirmed the theory of plate tectonics, explaining earthquakes, volcanic activity, and changing formations on the ocean floors. This manuscript map, believed created in 1977, shows the work of Heezen and Tharp, hand painted by Heinrich Berann, an artist who worked with them over a long period of time. It superimposes new data on the seismicity of the Earth to illustrate clearly how earthquakes follow the Earth's shifting plates.

The collection consists of primary data, including ship tracks and bathymetric soundings, bottom profiles, geologic and hydrologic data, information on gravity and magnetism, earthquake and seismic data, and a variety of water and ocean current data. In addition, secondary data in the collection consist of contour information, province maps, and Tharp's special domain—physiographic diagrams that she drew by hand. Tharp's hand-drawn, original manuscript maps of ocean floors are based on systematic study of each ocean's depths and contours. The maps provide compelling evidence of her contributions to geographic knowledge. Rounding out the collection are globes, photographs, undersea cable data, various worksheets, preliminary drawings, and published maps used for points of reference.

In the course of their laborious work, Tharp and Heezen made a remarkable discovery. The Atlantic Ridge had long been known to exist, but what was not known was that there was a valley down its center. It was here that the continental plates were spreading as new material rose from the ridge itself. Dating of the rock proved that the material on both sides of the valley became older as the distance from the valley's center increased. It took Tharp almost a year to convince her male colleague of the accuracy of her findings before he was willing to publicly acknowledge their discovery.¹⁷

In addition to Tharp, there are legions of twentieth-century women who have worked in various settings as engravers, geographers, and cartographers, particularly in government agencies where individual authorship is seldom acknowledged. Once again, the true extent to which women have participated in the accumulation of knowledge about the earth and who have made maps has been obscured by the erroneous perception that geography and cartography are primarily male disciplines.