This paper makes no contribution to general theories of reef-formation or to detailed studies of ecology. It attempts to summarize provisionally various observations, from scattered outcrops and wells, on the stratigraphic relationships of some reefs in the Middle East.

The principal types are fringing-reefs, barrier-reefs, shoal-reefs, reef-knolls, and bank-reefs, the last term being used to indicate reef-complexes formed over submerged highs, generally of tectonic origin. It is shown that, under ideal conditions, the back-reef, reef, and fore-reef (basinward) facies-zones of a reef-complex can be differentiated by petrographic and micropaleontologic criteria recognizable in thin sections, even of well cuttings; and that by this means it is commonly possible to infer the position and history of a reef from a series of local observations.

The term "reef-complex" is applied to the aggregate of reef limestones and the calcareous rocks genetically (?) associated with them.

The zone of interdigitation between a reef-complex and the basinward sediments is considered to be particularly favorable for the generation, migration, and accumulation of oil, subject to certain conditioning factors such as the relative development of primary and secondary porosity; or of primary or secondary lime cementation in fore-reef limestones which, if porous, may act as carrier beds and reservoirs.

It is shown that the reefs grew in certain sub-littoral zones and on some submerged highs of epeiric seas covering the Arabian foreland, in which deposition of the globigerinal chalk-marl facies predominated.