Oolite

Oolite, or Roe-stone, a limestone made up of rounded concentric grains resembling the roe of a fish, each grain being formed round a minute grain of sand, fragment of coral, shell, or other body. It would seem to have originated in lagoons or enclosed areas of sea, where the water could become concentrated and gentle currents keep the grains in motion. Some Carboniferous limestone is oolitic; but those of our English Jurassic (q.v.) rocks are so markedly so as to be often termed the Oolites. Bath-stone is very typically oolitic. When the grains are as large as peas, the rock is called a pisolite or pea-yrit, which is much less common.