268 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



immense reef flat flanking the lagoon side of the southern face of Taritari. 

 The cementing of slab shingle on the top of the Millepore heads killed by 

 Nullipores shows how living and dead corals may alternate and strata be 

 passed through in which some coral is found in its natural attitude, while 

 the rest appears as if it had been transported by the sea a considerable 

 distance. This certainly is not the case on the extensive flats of Taritari, 

 where the old material, or rather the dead material, is still in place occupy- 

 ing the position it had when forming a part of the great living coral reef 

 flat of the lagoon. 



On the lagoon flat to the west of the village of Butaritari (PI. 159, fig. 1), 

 the Porites covering the flat have been killed by a process identical to 

 that which has changed the great thriving Millepore reef of the eastern 

 part of the atoll into a shallow flat, over which are scattered small slabs 

 of Nullipores, and fragments of dead Millepores, the whole covered with 

 coral sand and ooze. On the wide Porites flat forming the extremity 

 of the land rim to the west of Butaritari, certain parts have been cut off 

 along given lines by accumulations of material derived from the dead 

 Porites and have enclosed limited areas constituting secondary lagoons. 

 Scrub vegetation, forest trees, grasses, cocoanut trees have sprung up on 

 the bars thus formed, and from the decay of the vegetation and the killing 

 of the Porites in the enclosed areas by exposure or by the growth of 

 Nullipores, the shallow circumscribed flats have gradually been filled, leav- 

 ing only indistinct areas, occupied by pools separated by belts covered with 

 vegetation, slightly higher than the general level of the western part of the 

 island west of Butaritari. 



The high coral shingle beach on the western face of Butaritari, the 

 great shingle and boulder dam, extending north from the southern point 

 on the very edge of the outer reef flat, and the great sea wall running north 

 from the eastern point of Taritari, all clearly indicate how the wide reef 

 flats of these faces of the atoll have been shut off from free access to the 

 sea, and how an outer barrier has been formed behind which the land rim 

 of Taritari has slowly developed. 



The first indication of the formation of an islet on the outer reef flat con- 

 sists of a line of coral shingle thrown up to a height of not more than four 



