Davis. — Signified ni Features of Ecef -bordered Coasts. 7 



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 I.slands. — 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 some- 

 what cliffed, and but little fringed with corals. Reunion, 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 cUffs 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 do^vn 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 sub- 

 mergence 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 upgrow- 

 ing 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 



