Gerard Mercator

2) The cusps seem to form most easily when there is a vertical stratification of material, with relatively coarse shingle at the surface and a mixed, impermeable layer a few inches beneath. This can be quite simply explained in terms of the mobility of the material in the swash zone; an underlying impermeable layer reduces the percolation of the swash through the beach and so increases the power of the waves to move the shingle. Further the heaped shingle on the cusp promontories is more permeable than the thinner layer in the bays, and consequently is less subject to erosion. This con? tributes to the relative permanence of the cusp system. (3) Waves whose height is too great for the dimensions of the cusps tend to sweep over the cusp promontories and destroy them

Cartography · Geography · Mercator projection · Geology · Maritime and Coastal Archaeology