While the geometry shown in this cross section and in the block diagram would be considered a very reasonable Valley and Ridge (or any “thin-skinned” sedimentary fold-thrust belt) structural style today, conceptual models of Appalachian Valley and Ridge geometry were somewhat different in 1964. Drilling was expected to encounter the Cambrian quartzite (green in the block diagrams) at just under 11,000 ft (3,353 m) deep because faulting beneath anticlines was believed to involve crystalline basement rock (gray in the diagrams) and cut across sedimentary layers at constant angles, regardless of the mechanical properties of the layers.