The development of salt domes is formulated as a case of Taylor instability in the salt-sediment system. It is assumed that the salt layer rests on a rigid substratum, while the upper surface of the sediment is free. Both salt and sediment are assumed to behave as highly viscous media. Of the entire spectrum of infinitesimal perturbations the component of the fastest growth is assumed to become dominant and to determine the spacing of domes.Exact solutions are derived for the linear theory in equations (3.7) and (4.24). Corrections due to the nonlinear terms are analyzed qualitatively in (5.8) and (5.9).