A model is presented for the motion of a single species of ion into shale. Ions and solvent (water) flow along a channel, the walls of which consist of charged clay particles. The clay is surrounded by electrical double layers, and the two sides of the channel-repel each another. The final separation of the clay particles depends upon the applied stress. If this is sufficiently small, the channel will swell even when placed in contact with an external reservoir containing concentrated electrolyte. However, the rate of swelling will be slower when the concentration in the outside reservoir is increased. The direction of motion of the ions and solvent need not be the same. Examples are given in which ions flow into the channel, but solvent flows out. As time proceeds and the swelling front moves along the channel, the motion of solvent (or ions) at any given point may change direction. Results are also presented for the potentials generated both by changes in ionic concentration and by fluid flow.