Page:Memoirs of the Geological Survey of Great Britain, Volume 1.djvu/26

Rh such cases the bank of shingles often accumulates, and behind, as at L, estuary deposits of mud and sand are effected.

In travelling from A to B, where we suppose, for illustration, a point of land jutting out into deep water, and a river at D, with water in it, in its ordinary state, not sufficient to contend with the piling influence of the breakers, the shingles would pass forward gradually to B, their progress being only interrupted for a short time by floods at D, during which there might be a free passage through the shingle barrier.

Arrived at B, the pebbles would no longer keep within the influence of the breakers to be forced onwards, and they would, as it were, be shovelled into the deep water, accumulating in a kind of heap, the gradual additions to which would indeed produce some effect in collecting a mass of shingle, resting on the base of the cliff under water.

In such cases we may have the broken remains of shells among the shingles within the influence of the breakers; while some of the same kind of animals which produced such shells, with other animals, may exist undisturbed amid the pebbles thus forced into the deep water; so that this continuous mass of pebbles would, if lifted above the sea, be found to contain broken shells in one place, and whole shells, some even such as Serpulæ, tending to cement the pebbles together, in another.