Sea caves are formed by the constant action of waves which attacks the weaker portions of rocks lining the shores of oceans and large lakes. Such caves testify to the enormous pressures exerted by waves and to the corrosive power of wave-carried sand and gravel. In desert areas, some shallow caves may be formed by the sandblasting effect of silt or fine sand being blown against a rock face. These eolian caves, some of which are spectacular in size, are surpassed in number by caves of other origins in most deserts. More common even in the driest deserts are sandstone caves eroded in part by water, particularly if the sandstone is limy.
Most wind caves are, in fact, solution caves.
The melt-water streams draining out along the floor of a glacier cave or the surging, pounding waves at the mouth of a sea cave offer immediate evidence of the origin of these caves. Solution caves, however, have always been a source of wonder to man. After a rain, water seeps into cracks and pores of soil and rock and percolates beneath the land surface. Eventually some of the water reaches a zone where all the cracks and pores in the rock are already filled with water. The term water table refers to the upper surface of this saturated zone.