PHYSIOGRAPHY OF THE PHILIPPINE ISLANDS: II. 21 



the extent of this at any given point depends upon the strength of the 

 shore current at that point. The features (c) and (d) belong to periods 

 of moderate weather and hence are constantly being destroyed and 

 rebuilt. 



It is clear in the case of the cliffs of poorly consolidated conglomerate 

 surrounding the northern part of Batan, that they could not retain their 

 present form without constant cutting by the waves. Hence, the land 

 can not be rising, for otherwise the elevation of the bench would cause 

 the waves to trip before reaching the cliff, and the cliff, left to the disin- 

 tegrating action of the atmosphere and groimd waters, would slump down 

 until the angle of rest of its material is reached. On the west coast of 

 Isbayat there is a considerable depth of water very near the shore and 

 there is no beach between the cliffs and the sea. This indicates recent 

 depression. 



TIDAL SCOtTR. 



The tidal scour is another marine agency which must have considerable 

 effect. The tidal wave between the Pacific and the China Sea must pass 

 through the Bashi and Balingtang cliannels. Consequently, the wave 

 is narrowed, its force increased and an extremely complex series of strong 

 tidal currents is created throughout the islands. It is to be expected 

 that these currents should have some effect upon tloe submarine con- 

 figuration and it seems likely that the channel of Santo Domingo Bay 

 and that between Sabtan and Ibujos while possibly of terrestrial origin, 

 owe their present depth and preservation to tidal scour. The depth at 

 present of the channel between Y'Ami and May sanga is undoubtedly due 

 to the tide. 



COEAL. 



The upbuilding accomplished by the coral is opposite to the destruc- 

 tive agencies of waves and tide. There are few coral reefs in the more 

 exposed portions of the islands, such as the northern and eastern coast 

 of Batan, but growing coral is found everywhere in the more sheltered 

 portions. Beginning on the north side of Santo Domingo Bay there is 

 a series of small coral reefs extending along the west and south shores 

 of Batan as far as Disiai Point. There is only a small amount of coral 

 growing in Santo Domingo Bay, probably because of the sediment brought 

 down by the stream from Mount Iraya ; the reef is also broken by small 

 channels, due to streams, which determine the position of the barrios of 

 San Carlos de Magatao, San Vicente, San Jose de Ibana, San Antonino 

 and Itbod. Besides this the points of Chaua, Mabatuy and Mabien stand 

 out beyond the reef. The reef on Sabtan is more extensive, forming a 

 barrier around the island which is broken only by small channels at San 

 Vicente, Santa Eosa and Santa Ines, and at Natao and Ajao Points. 

 There is no inlet at the barrio of San Luis, making it necessary to launch 



