Crustal structure of the southern Appalachians and adjacent Interior Low Plateaus in Tennessee is derived from seismic-refraction measurements observed by the U.S. Geological Survey in 1965 along reversed lines, normal (NW-SE) and parallel (NE-SW) to the structure of the Appalachian Highlands' major geologic divisions. Its easternmost part is located approximately 80 km southwest of the westernmost part of the COCORP seismic-reflection traverse within the Blue Ridge province. The velocity-depth models derived for both observational directions consist of three crustal layers with surprisingly high velocities, being about 6.1-6.2 km/s in the upper crust down to 7-10 km depth, 6.7-6.8 km/s for the middle crust between about 17 and 34 km and varying from 7.1 to 7.4 km/s for the lower crust at about 40-47 km depth. The boundaries between the three crustal layers as well as the crust-mantle boundary are transition zones of up to 11 km thickness. Similar to old orogens in other parts of the earth, the main result is a thick crust, at places in excess of 50 km, with high average velocity and a broad crust-mantle transition zone. ?? 1984.