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Transactions. 



shallow seas may ])erliaps be thus explained ; but, as this aspect of the 

 problem has been little considered by observers on the ground, the chief 

 object of this paragraph is to stimulate local and critical observation rather 

 than to announce an assured conclusion. / 



Cliffed Coasts, partly submerged. 



Since the proposal of the glacial-control theory of coral reefs (Daly, 

 1910 ; 1915) it has become important to note whether the spur-ends of 

 embayed coasts inside of fringing or barrier reefs are cut off in cliffs 

 that descend steeply below sea-level. That theory assumes that mid- 

 Pacific volcanic islands have long stood still, and that their embayments 

 occupy valleys which were eroded while the ocean was lowered during the 

 Glacial period. It assumes furthermore that the lowered ocean was chilled 

 sufficiently to kill the corals and other organisms of coral reefs, so that 

 the reefs would be cut away, probably at some such level as 40 fathoms 

 below the present ocean-surface. 



Now, if these assumptions are correct, it follows that an embayed island, 

 like Murea in the Society Group, which is now surrounded by a barrier reef 

 about half a mile from the shore, must, after its corals were killed and its 

 reef was cut away by the waves of the lowered sea, have been strongly cut 

 back in cliff's ; for, if the sea were actively abrading the island during a 

 period long enough for the excavation of the open valleys now occupied by 

 arms of the sea, the spurs between the valleys must have been cliffed. Be 

 it remembered here that, according to the testimony of volcanic islands in 

 the temperate oceans, the retreat of cliffs under the attack of sea-waves is 

 more rapid than the deepening of valleys by streams, and hence all the 

 more rapid than the slow widening of valleys by the weathering of their 

 side slopes. Rock-resistance need not be considered, for it will affect cliff- 

 cutting and valley-widening in similar fashion. 



It is evident, therefore, that close attention should be given to the forms 

 of spur-ends where they disappear in the lagoons of barrier reefs, particu- 

 larly where the barrier reefs are not far off shore. If the spurs are cut off 



Fio. 4. 



in bluff's, B (fig. 4), from 10 ft. to 50 ft. in height, in front of which 

 rock platforms extend from 30 ft. to 100 ft. forward, such bluffs and plat- 

 forms must be attributed to wave-action at present sea-level, as has been 

 explained above. 



If, on the other hand, high spur-end bluff's or cliff's, LH, are found but 

 no rock platforms are visible in front of them, and if (except for a narrow 

 fringing reef) the lagoon has depths of 10 or 20 fathoms near the cliffed 

 spur-ends, then the cliffs should be attributed to wave-action producing a 



profile HCP when the sea was lower or the land was higher than now. 



As 



