SOIL FORMATION: ROCK DISINTEGRATION. 317 



of the atoll. On a portion of this ring grow certain grasses and 

 carices. The soil for some depth shows a wet peat made up of 

 decaying grasses, carices, and much peat moss (sphagnum). 

 In some places one element seems to predominate, and in other 

 cases another element. On some portions of the outer ring are 

 shrubs one to three meters in height, and occasionally small 

 trees have gained a foothold. 



Next inside of this belt is a broad, level zone, with Carex 

 filiformis, other carices, grasses, with a few dicotyledons. 

 Intermingled are various mosses and much sphagnum. The 

 soil formation underneath contains remains of carices, grasses, 

 and sphagnum. This intermediate zone is not a homogeneous 

 one. At certain places are extensive areas in which Carex 

 filiformis predominates, while in another place another carex, 

 or grasses predominate. 



483. A floating inner zone. — But the innermost zone, that 

 which borders on the water, is in a large measure made up of 

 the leather-leaf shrub, cassandra, and is quite homogeneous. 

 The dense zone of this shrub gives the elevated appearance to 

 the atoll immediately around the central pond, and the 

 cassandra is nearly one meter in height, the "ground" being 

 but little above the level of the water. As one approaches 

 this zone, the ground yields, and by swinging up and down, 

 waves pass over a considerable area. From this we know that 

 underneath the mat of living and recent vegetation there is 

 water, or very thin mud, so that a portion of this zone is 

 "floating." 



The inner, or cassandra, zone is more unstable, that is, it is 

 all " afloat," though firmly anchored to the intermediate zone. 

 The roots of the shrubs interlace throughout the zone, firmly 

 anchoring all parts together, so that the wind cannot break it 

 up. Between the tufts of the cassandra are often numerous 

 open places, so that the water or thin mud on which the zone 

 floats reaches the surface, and one must exercise care in walk- 

 ing to prevent a disagreeable plunge. No resistance is offered 



