For gravimetric investigations, a naturally occurring limestone cave may be compared with a buried empty sphere or cylinder, depending on its shape. The practical limit of detection for a subsurface void, utilizing available equipment (Worden gravity meter) and standard field procedure, is 0.1 milligal. Most corrections normally required by the gravimetric method may be neglected in cave detection, but the altitude control for the field traverse must have an accuracy of ± 0.1 foot. The detectability of a limestone cave, based on field work done at Luray Caverns, Virginia, and at other localities, is related to its shape, Radius (R), and distance from surface to the cave center (Z). It follows a non-linear relationship. Detectability is possible only when R3/Z2 = 4.3 feet and R3/Z = 2.89 feet. For a cave room and a cave passage respectively.