One hundred and fifty years ago, Michael Tuomey completed his 'Report on the Geology of South Carolina,' the result of four years of arduous labor. The report is the first detailed and comprehensive geological description of the entire state, and it includes a geological map that shows the distribution of Coastal Plain and Piedmont-Blue Ridge units. In the sesquicentennial of Tuomey's survey, it is fitting that we recognize his important early contribution to the geology of South Carolina and the southeast. Tuomey's report is a 293-page volume with a 48-page appendix and an index. Although he gave a complete depiction of Coastal Plain geology and delineated Cretaceous, Lower Eocene, Eocene, Miocene, Post-Pliocene, and alluvial units on his map, the emphasis herein is on his mapping of the Piedmont and Blue Ridge. The metamorphic units he delineated are clay slate, mica slate, talcose slate, hornblende slate, gneiss, and lime rock. Gneiss is the most extensive unit on the map. His map shows many elements of the geologic framework we recognize today. The distribution of his clay slate unit corresponds closely with the Carolina slate and Bel Air belts as we know them now. The gneiss between the two clay slate areas matches the Kiokee belt. Areas of mica slate approximate the northern part of the Kings Mountain belt and the Chauga belt. He also recognized that his talcose slate unit was associated with gold deposits. Granitic and basaltic intrusive rocks are also delineated on the map. It shows the Newberry, Columbia, and Liberty Hill granites we recognize today. Basaltic intrusives outlined include the Bush River of western Newberry County, Dutchmans Creek, Big Wateree Creek, and Ogden gabbros. He described the regional extent of diabase dikes as occuring from Virginia to Alabama, noted their preferred direction and diagrammed their near-vertical orientation. He also referred to the distinctive soil and topography that develops on the large gabbros. Michael Tuomey's report is truly a benchmark publication, for sixty years passed before the next statewide survey was done. Upon completing the report, he left South Carolina to become director of the Alabama Geological Survey.