In 1946-1947 two deep tests, one on the Cincinnati arch in Kentucky, and one on the Nashville dome in Tennessee, were the first wells to penetrate the entire sedimentary section in this geologic province.

The California Company's A. R. Spears No. 1, located 1.7 miles northwest of McKinney, Lincoln County, Kentucky, reached the total depth of 6,117 feet, stopping in rhyolite porphyry, probably pre-Cambrian in age. This test was drilled on a local anticline on the south plunge of the Cincinnati

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arch. Starting in the lower part of the Tate formation of the upper Ordovician, the well penetrated 418 feet of argillaceous limestones and shales of upper Ordovician, Maysville, Eden, and Cynthiana groups; 191 feet of middle Ordovician, Lexington limestone; 651 feet of lower Ordovician, Wells Creek dolomite; 2,936 feet Cambro-Ordovician dolomite probably more or less equivalent to the Knox dolomite group of Tennessee; 137 feet of Cambrian limestone and dolomite with minor amounts of gray shale tentatively correlated with the Maynardville limestone; 739 feet of Cambrian reddish brown and gray shales with some fossil fragments, and gray interbedded siltstones, considered to be in part correlative of the Nolichucky formation; 615 feet of quartzitic sandstone with intercalated green and ray shales and siltstones that may be middle or lower Cambrian in age; 25 feet of Cambrian or pre-Cambrian limestone, the lower part containing pebbles of rhyolite; and 356 of rhyolite porphyry, probably pre-Cambrian in age.

The California Company's E. W. Beeler No. 1, located 1/3 mile southwest of Campbellsville, Giles County, Tennessee, reached the total depth of 5,750 feet, stopping in granite, probably pre-Cambrian in age. This well is on a prominent local closure on the southwestern extension of the axis of the Nashville dome. Starting in limestone of the Carters formation of the middle Ordovician, this well penetrated 660 feet of middle Ordovician, Black River-Stones River limestone; 69 feet of lower Ordovician, Wells Creek dolomite; 4,571 feet of Cambro-Ordovician dolomite probably correlative of the Knox and Bibb-Ketona-Brierfield groups; 338 feet of Cambrian calcareous and shaly dolomite; 77 feet of quartzite and quartzitic sandstone, Cambrian or pre-Cambrian in age; and 45 feet of granite.

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