In addition to the recent discovery of a Proterozoic sandstone with natural-gas potential in the central Kentucky part of the basin, an ancient eroded mountain belt, called the Hoosier thrust belt, was discovered lying farther northwest in the English Basin part of the East Continent Rift Basin of Kentucky and southern Indiana. This mountain belt appears to have formed as the result of contraction developing during several episodes of orogeny during the Proterozoic. The thrust and fold structures of the eroded mountain belt also form potential natural gas traps that need to be evaluated by deep drilling. These structures were first recognized in northern and western Kentucky, but recent availability of seismic data in southern Indiana has greatly enhanced our understanding of their distribution. Overlying the fold and thrust structures are two later Proterozoic sequences; the younger sequence shows no contractional structures, indicating the termination of regional compression. An understanding of these deep Proterozoic sequences and their effect on overlying Paleozoic rocks is important to future petroleum resource exploration, CO2 sequestration, and other waste-disposal programs, and in understanding mechanisms that cause earthquakes.