THE ISLAND BEACHES 173 



This sand is made in many ways wliich will need detailed 

 examination, but the most important of all the agents in its 

 making are the grinding movements of the wave-driven 

 boulders on the shore platform, and the myriad beaked Scari 

 which are perpetually reducing dead coral masses to fine 

 sand. 



The sand is the lightest of all the degradation products of 

 the coral, and is carried the farthest both by the waves and 

 by the wind ; it is the fluctuating currency of the land, and 

 is deposited and swept away, accumulated and withdrawn, as 

 it makes and unmakes new land. In all the fluctuations of 

 this sand movement there is a compensation, and if a westerly 

 wind piles up the lagoon shore a foot higher with sand at one 

 point of the atoll ring, it has robbed some other part, and has 

 left a breccia platform exposed, instead of a gently sloping 

 sandy beach. 



The great extent of the inner margins of the island ring con- 

 sists of this white sand beach on which lines of agar-agar, and 

 other lagoon algse, mark the excursions of the tide ; but in 

 places it is broken by breccia platforms, exactly like the shore 

 platforms of the seaward barrier. These rock layers, often 

 broken and displaced by the sucking action of scours and 

 eddies, stretch out from the accumulated island sand and 

 run far into the lagoon, becoming continuous with the dark 

 patches which break the stretches of blue-green water, and 

 mark the site of the lagoon breccia rocks. 



It must not be imagined that these breccia slabs, found on 

 the lagoon shore, have been formed in situ under the present con- 

 ditions. The only site of typical breccia formation is the surf- 

 beaten barrier, and the breccia slabs of the lagoon shore were 

 laid down in the distant past, when the present lagoon shore 

 was the wave-beaten outpost of the island plateau. Although 

 typical breccia — the well-consolidated mosaic of coral frag- 

 ments — is not formed on the lagoon shores, yet the same 

 forces that produce the seaward breccia are always acting in a 

 lesser degree on the lagoon shore. The gentle lapping waves 

 of the lagoon shore are for ever tending to weld sand particle 



