THE LAGOON 199 



white coral sand ; and the whole beach raised again by the 

 agency of the wind and waves. He would even see, in all 

 probability, a series of little terraces made in the sandy shores 

 as gradually waning high tides built to their maximum levels ; 

 then he might possibly think that the land was steadily gain- 

 ing on the sea. It is always assumed in estimating any 

 changes in the shore-line that the surface of the ocean stands 

 constantly at the same level, and yet, strange though this may 

 appear, it is not always safe to assume this. It is apparently 

 one of the strange phenomena of far-out blue water that its 

 mean surface-level is subject to considerable variation. Of 

 this strange fluctuation in level, such a place as the atoll forms 

 a very interesting index — it is the Plimsoll-mark of the 

 ocean's variations. During my stay in the islands I have seen, 

 for a week at a time, and without any variation in the tides, 

 the curious condition of the barrier never being once exposed 

 at low tide. The tides went through their usual excursions, 

 the high tide being higher than normal, and the low tide not 

 so low as normal ; but the whole surface-level of the ocean 

 was set at a higher plane than was ordinary. This state of 

 affairs is doubtless brought about by the banking up of the waters 

 of the Indian Ocean, and the event happened after a report had 

 come over the cable that a violent storm of long duration had 

 raged in the neigbourhood of the island of Rodriguez. It was 

 the time of neap tides, and so the increased high tides did not 

 reach the striking level that they would have done had the 

 event happened during spring tides ; but the phenomenon was a 

 very striking one. It is easy to see that if a change of ocean- 

 level — even of very brief duration — were to be accompanied 

 by a combination of high winds and spring tides, imprints 

 would be left on the islands which might appear to indicate a 

 shore movement of several feet. It would not be at all likely 

 that these appearances would be rightly interpreted by a 

 visitor to the atoll who had not seen the process in its 

 making. 



The average tidal variation is from three to four feet, and 

 the tide's turn takes, as a rule, about an hour and a halt" to 



