A Monograph of Marcus Island. 91 



corals iu the centre of the growth die from want of suitable food, 

 and as a rule a simple lagoon surrounded by a ring of coral results. 

 Through the acftion of the waves fragments of coral are detached 

 from the outer edge of the reef and piled on its surface together 

 with shells and other land-building materials. In the lagoon, 

 which at this time must have been more or less cut off from the 

 sea except iu the periods of storms, there begins to form an ooze 

 which is augmented by the decaying vegetable matter supplied 

 from the hardy shore plants growing on the ring of new formed 

 land about it. 



Located as our embryo island is iu the regions of the terrific 

 monsoons that sweep over the west and northwest Pacific, it is not 

 difficult to account for the frequent appearance of small fragments 

 of pumice and other light volcanic produdls that, floating on the 

 surface of the ocean, have eventually been carried over the ring of 

 sand and shingle and deposited in the comparatively quiet water of 

 the lagoon and there mingle with fragments of coral, bits of shell, 

 and other forms of ocean debris which are brought thither from 

 time to time. 



We have no definite clue as to the time required to build up the 

 land to the greatest height it can attain from the ordinary aClion of 

 the sea ; but from the charadler of its surface at the highest points, 

 consisting as it does of boulders of coral twelve inches or more 

 in diameter, which are mingled with smaller fragments, we are 

 able to leave out of account the a(5lion of the wand that is so 

 frequentl)' a potent agent in building coral islands above the high 

 water mark. Investigators have determined that the highest waves 

 are but little more than a third the height of this island (75 feet), so 

 that we must look elsewhere for the agencies that would build up 

 this heap of sand and shingle to its present height. Perhaps the 

 most apparent and convincing testimony would be derived from a 

 study of the 6x\ lagoons and the material which forms their floor. 

 Mr. Sedgwick made excavations in all four of these, but especially 

 in the larger central one which is designated on the map. Review- 

 ing the conditions found there it would appear that at a time when 

 the island had been piled up to the height of thirty or more feet, 

 the ring of land, lagoon and all, had been of a sudden subject to a 

 uniform uplift. Gradually this lake-like lagoon had evaporated or 

 leached out through its porous bottom, leaving a deposit of black 



