346 J. Stanley gardiner. 



300 feet on to the reef, as well as the remains of two series almost parallel to the beach 

 at distances of 270 and 530 feet from the same. 



The action, which forms the rock, is quite clear and requires little comment or explana- 

 tion. The sea twice in the 24 hours covers and recedes from the beach. In a tropical 

 region the sand may be said to be twice wetted and dried. In the latter process the salts 

 in the sea-water are deposited on the sand grains. Some are at once redissolved on the 

 tide again covering the beach, but the carbonates and the sulphate of calcium largely remain, 

 in course of time filling up the interstices between the sand grains and binding them 

 together. The sulphate of calcium later becomes largely replaced by the less soluble carbonate, 

 a rock being ultimately formed of almost pure carbonate of lime. The rock is naturally 

 built from the surface downwards, the drying up and fresh wetting by the sea being mainly 

 superficial. The thickness of the layers, 5 or 6 inches in the Maldives, probably represents 

 the mean depth to which the drying up of the surface is effective at low tide. That the 

 sand must be formed necessarily in the first place of almost pure carbonate of lime remains 

 is probably due to the more powerful attraction that bodies of the same or like constitution 

 have on one another together with the restriction of the variety of the crystalline forms 

 that would occur in the beach ^ 



From the consideration of the foregoing account of the beach sandstone it will be obvious 

 that almost any conceivable complication may arise in its appearance and distribution off 

 any island that may be washing away. In nearly all cases the slope of any mass is that 

 of the beach, of which it originally formed a part. The masses in course of time become 

 more and more indurated with carbonate of lime and of great density and hardness. Where 

 the beach is washed away and they lie on the flat, the terrace arrangement may disappear, 

 and they will then become separate, long, irregular blocks, more or less rounded at the top. 

 In this state they resist the action of the sea even more than the coral conglomerate, and 

 where all remains of the latter may be lost these masses often are left. It is obvious then 

 that from the study of such masses off any island or on any reef the former extent and 

 contour of the land may be deduced with considerable certainty. The erosion of land in 

 the Maldives, the formation of flats at about the low tide level by the washing away of 

 the land and the hollowing out of such flats to form first pools, then velu or definite lagoons, 

 may absolutely be traced. The facts speak for themselves, and — if my views as to the 

 formation of this rock be correct, of which I can have no doubt — I claim to give indubitable 

 proof that the conceptions of Murray as to the formation of lagoons and my own opinions, 

 enunciated in Chapter VII. of this j)aper, rest on a firm and correct basis. 



' The skeletons of the organisms that form the sand are in the instances mentioned above (p. 343), is not however 



generally of calcite or arragonite. Most of the deposit of quite clear. 



calcium carbonate is in the first place in the amorphous It is interesting to notice that the natives of Suvadiva 



state, subsequently metamorphosing to the crystalline form make use of this indurating action of the tidal waters to 



of the remains of the organism nearest to it. This deposition harden the corals of which they make gravestones. The 



of amorphous material may be due to the constant presence coral — generally a mass of Pori'teareHOsa — is roughly squared 



of a small trace of organic matter, hindering crystallisation. and then deposited for a year on the beach between tide 



The reason why a relatively small amount of organic marks so that the pores may be filled up, the whole then 



matter should prevent the formation of beach sandstone, as wearing much better when placed in position. 



(To he continued.) 



