Davis. — Significant Feattires of liitf -bordered Coasts. 11 



duration of the post-emergence or post-submergence stationary period, 

 the estimation of which may now be considered in some detail. 



Time since Emergence. — The shore-line of an emerged and thence- 

 forward stationary coastal plain may be locally built forward, or 

 " prograded," by deltas if its rivers are of large volume and well charged 

 with detritus from an elevated backland ; and sand reefs enclosing 

 shallow or marshy lagoons may be cast up by the waves between the 

 deltas, and may advance seaward as the delta-fronts advance. Conditions 

 of this sort appear to prevail along the Madras border of India, and 

 around the south-west side of Borneo, thus proving that these coasts 

 have been somewhat changed from their simpler initial form ; but the 

 littoral conditions are still manifestly unfavourable to coral-reef formation. 



It is conceivable, however, that after a temporary supply of gravel 

 and cobbles has been washed out by a flooded river to a certain part 

 of the front of a delta that is for the most part composed of finer 

 sediments the river may change its course, as rivers on deltas are prone 

 to do. Then corals, attaching themselves to the larger cobbles, may 

 spread sufficiently to form a small fringing reef, until a return of the 

 river buries the corals. A buried reef of this kind will slant forward 

 with the delta-front, and will lie conformably between the earlier and 

 later foreset delta-beds. Such seems to have been the origin of a small 

 elevated reef near Suva, Fiji : it lies on a local deposit of gravel, and 

 both the gravel and the reef lie conformably in the slanting beds of 

 volcanic mud, there known as '' soapstone." 



The extent of the littoral lowland that is prograded along the border 

 of a coastal plain will give some idea of the time that has elapsed since 

 the plain emerged. But such lowlands are not always developed ; for, 

 if large rivers are wanting, the shore-line of a coastal plain may be cut 

 back or retrograded farther and farther by the sea, as long as no change 

 of level takes place. The farther it is cut back, the higher will be the 

 resulting bluSs along the coastal-plain margin. The height of the bluffs 

 along the shore of a retrograded coastal plain will therefore give an 

 indication of the time during which it has been attacked by the sea. 

 A more important point is that, however far such a stationary coast may 

 be retrograded, a beach of loose detritus, continued off shore by a sheet 

 of finer sediments, will, according to accepted physiographic theory, always 

 cloak the abraded ^^latform along the base of the retreating bluff's. No 

 reefs are therefore to be expected on such a coast. 



The ReeJ-free Coast of Madras. — It is important that the coasts of 

 the coral seas should be examined with these principles in mind in order 

 to test their correctness. As far as I have read, there is no published 

 account of a strongly retrograded coast in the torrid seas that is still 

 suffering abrasion in its original stand with respect to sea-level. It is 

 interesting to note, however, that the high, hard-rock cliffs which, as 

 described by Gushing, rise a short distance inland on the coast of Madras 

 appear to have been cut back by the sea before the emergence of the 

 present Madras coastal plain ; hence the cliffs must, before the sub-recent 

 movement of emergence by which a negative shift of the shore-line was 

 caused, have exemplified a maturely retrograded, reef-free coast ; and 

 at the beginning of their abrasion the hard-rock land-mass must in all 

 probability have been covered, near its shore-line at least, with the sedi- 

 ments of an ancient coastal plain of emergence, just as the emerged 

 platform of marine abrasion which fronts the high cliff's is covered by a 



