suffered. Some coasts have a smooth seaward slope, and consist of imperfectly consolidated marine strata, dipping gently seaward, which have been little eroded since their emergence from the sea in which they were deposited: these are typical coasts of emergence. Other coasts, whatever their structure may be, exhibit forms of subaerial erosion, such as hills and valleys, the slopes of which appear to continue below sea-level, as if they had been partly submerged since they were eroded: these are coasts of submergence. Coasts of Emergence. — Along coasts of emergence of the kind above specified the shore-line will generally be almost rectilinear or of simple curvature. The amount of emergence may be inferred from the altitude to which the marine strata rise along their inland border. It may be at once stated that coasts of this kind are seldom fronted by coral reefs, apparently because the loose sediments of their beaches and submarine slopes do not afford a suitable foundation for coral-growth: witness the Madras coast of India, the south coast of Java, and the west and south coasts of Borneo, all of which bear marks of sub-recent emergence. Another class of coasts of emergence, on which coral reefs abound, will be given special description below. Young Volcanic Islands.—The coasts of young volcanic islands may be associated with coasts of emergence, especially if composed largely of ash and not of solid lava. They are frequently cliffed and beached, without reefs. Barren Island, east of the Andamans, in the Bay of Bengal, is somewhat cliffed, and but little fringed with corals. Réunion, in the western Indian Ocean, has reached a rather mature stage of erosion and abrasion, with a very imperfect development of fringing reefs, as will be further explained below. It therefore resembles certain strongly cliffed volcanic islands in temperate latitudes. Let it be noted that the cliffs of such islands are usually cut back by the waves at a faster rate than the valleys are cut down by their streams, so that the valleys are left hanging above sea-level, and their streams cascade down the cliffs to the beach. Coasts of Submergence.—On coasts of submergence the shore-line will necessarily be irregular, advancing seaward around the outstanding points of partly submerged spurs and entering landward around the branching embayments of partly submerged valleys. Conversely, shore-lines of this kind indicate that the coasts which they border have been submerged, as Dana pointed out in 1849. Singularly enough, Darwin never perceived the value of this evidence in support of his theory (Davis, 1913). The spur-ends of coasts of submergence in the coral seas usually offer excellent opportunity for the growth of fringing reefs, for their firm rocks are soon swept bare by the waves, and they are free from the detritus that accumulates in the bay-heads. If the submergence be slowly continued, a fringing reef, A (fig. 1), may be transformed into a barrier reef, B, by upward growth as the sea-level changes from S to T; but if the submergence be renewed at a more rapid rate, changing the sea-level from T to U, the barrier reef will be drowned, and, if a pause then occurs, a fringing reef of a new generation, G, will be formed, as will be more fully stated below. Unconformable Reef Contacts.—In all cases of reefs bordering coasts of submergence the original fringing reef which forms the base of an upgrowing barrier reef, as well as the lagoon deposits within the barrier reef and the secondary fringing reefs that grow on the spur-ends of the lagoon shore, and also all fringing reefs of new generations, must rest unconformably on