Continental geology and tectonics are explored through this study of modern beach sands of South America. This report assesses how well petrographic studies of sandstones can recreate continental geography. Data on the petrography of 218 modern South American beach sands are presented and analyzed. The five major mineral associations of light minerals that exist along South America's coastline are explained in relation to both the petrographic data and to onshore geology. Study results support the premise that the five mineral associations that were specified by the proportion of rock types and average values are rich in interpretive significance and can provide a basis for further inference on the tectonics and geography of a continent. Appendices include sand location lists and complete petrographic data of beach and river sands. Descriptive figures and tables are also provided. A three-page list of references is included. (ML)