34 J. STANLEY GARDINER. 



organisms, especially sponges, may work destruction. If the growth of the reef be vigorous, 

 the whole action of the latter may be neglected, the corals not being seriously weakened. 

 If on the contrary the conditions are unfavourable, whole masses of coral may collapse with 

 the slightest superincumbent weight into small grains, giving, with the solution and redeposi- 

 tion of the lime, great bricks, as it were, of structureless rock. Other skeletons suffer with 

 those of corals, but the solvent action is invariably more and the boring action less pro- 

 nounced. 



Above the sea- and tide-marks the first action on the same reef-rock is the solution 

 by the rain of the softer parts, sand, nuUipore, etc.^ Some of the water escapes cari-yiug 

 its lime, but a considerable portion percolates into hollows and is dried up, its lime serving 

 to consolidate the sand, etc. The water attacks the corals from the base, where they are 

 weakened by boring organisms, breaking them off and causing a sinking of the whole 

 surface, portion by portion. This continues until the crevices below are to a large extent 

 filled up with sand and fragments, more or less consolidated together. There results finally 

 a solid surface, strewn with coral blocks, which have less rapidly dissolved. A few chambers 

 may remain in the rock ; they either existed as such from the original reef, in which they 

 were closed in, or were subsequently dissolved out owing to the rain having ready means 

 of access and escape. 



Between tide-marks the action is more complicated by the wetting and partial drying 

 of the rocks by water, containing a large amount of calcium sulphate in solution, and 

 further charged with lime from the neighbouring shore and reefs. First the surface, ex- 

 posed to the tide, has its pores to some extent filled up by sand particles. It further 

 hardens, and becomes thoroughly indurated with lime, precipitated from the water, which 

 dries on the surface after each ebb. Yet withal solution is quite marked ; the waves 

 stream off by tortuous channels worn in the sand and nullipore formations between the 

 harder corals, which, if branched, are left as an upstanding forest of stems. Behind the 

 surface loose sand becomes more consolidated than where there is rain-water action alone. 

 The solvent action within the masses, save a little due to the rain, is inconsiderable, and 

 the whole differs very little from the original reef, except in its better consolidation and 

 the filling in of some of its interspaces. 



The conglomerate in Minikoi is found everywhere at the base of the outer beach, 

 especially at the points. Immense masses occur in the beach on the lagoon side of Kodi 

 point (PI. I. fig. 2), and continue in smaller pinnacles along the same shore, as far as 

 the rocky beach extends. The masses are much pitted and very rough on the surface 

 and of a slate-grey colour; they consist of a consolidation of corals, nullipores, shells, etc. 

 Between tide-marks the scour, sweeping the sand and pebbles to and fro, undermines and 

 finally precipitates the masses, to wear themselves beds perhaps in the rock beneath, to 

 which they may become consolidated. It follows then that no results can be obtained by 

 the examination of the smaller masses in respect to the position of the corals, etc., of 

 wliich they are composed. The large lagoon masses near Kodi point are of rough surface 

 with their corals freely exposed (Fig. 9). Madrepora is by far the most abundant genus 



^ These deductions are largely based on my observations and the adjacent islands. See Report Brit. Ass., p. 400, 

 on indubitably raised rocks iu the Fijies, but more particu- 1900. 

 larly in the northern districts of Ceylon, the Jaffna Peninsula 



