ABSTRACT
As mentioned in the previous chapter, reefs are a particularly important feature of carbonate shelves, and they deserve their own chapter. The term ' reef was originally applied to rocky prominences on the sea floor on which ships could be wrecked. Coral reefs are a particular form of this navigational hazard found today in tropical waters. Geologists have applied the term reef to lenses made of the calcareous skeletons of sedentary organisms. In many cases, however, it is not possible to demonstrate either that an ancient ' reef was a topographic high on the sea floor or, i f it was, that it was wave resistant. Cummings (1932) classified calcareous skeletal deposits into:
Bioherm ' A reef, bank, or mound; or reeflike, moundlike, or lens-like or otherwise circumscribed structures of strictly organic origin, embedded in rocks of different lithology' (ibid., p. 333).
