BEACH SANDSTONE. 343 



occurs on the beaches. In Ceylon, where silica is always met with to a very considerable 

 extent in some form or other in the beaches, my examination — extending round more than 

 the half of the coast-line of that island — failed to find any tyjaical formation of beach sandstone 

 or indeed any trace of formation at all, except where the land above was of coral origin. In 

 many parts the other conditions were perhaps not favourable, but in others looked eminently 

 so. In any case the presence of even 5 per cent, of silica seemed to prevent any extensive 

 building up of the sand of the beach into layers and terraces, typical of the appearance of 

 the beach rock on coral islands. At Rotuma off Noatau, Oinafa and Pepji', where a typical 

 formation exists, the beach was built up of almost entirely the same constituents as those which 

 form the shores in the Maldives, the land in Rotuma for some distance behind the beach being 

 in the above positions of coral formation. 



Even the finest textured specimens of the sandstone show their constitution to the 

 unaided eye. Of the very numerous pieces, which I broke off, none were in any way 

 homogeneous, but all could be clearly seen to have been formed of sand grains of varying size. 

 Where the sand was of extreme fineness, no rock was ever found. Minikoi has near the 

 village on the lagoon side, where the conditions appear in many places exceedingly favourable 

 for the formation of the rock, such a sand on its beach, but there is no trace of any 

 consolidation into rock. Along the west side of Hulule, the sand is perhaps a trifle coarser 

 but there is no sandstone except near the south point, round which coarser material is swept 

 up on to the beach. Of coarseness there is no limit, the rock sometimes consisting of 

 pebbles with the interstices filled in by sand. Indeed, it is only essential that there shall 

 be such an amount of the latter that the surface of the beach is smooth, all the interspaces 

 being filled in by the sand. The coarsest material on a beach is naturally found at its base, 

 and in correspondence the sandstone usually increases in fineness, the higher it lies above the 

 low tide level. 



The beach sandstone is everywhere in the Maldives perfectly distinct fi-om the raised 

 rock of the islands, which is a submarine formation difiering radically in its constitution. 

 Both rocks, if in the same position, i.e. on the beach, would be affected by the same conditions, 

 and might hence in external appearance resemble one another. The structure of the raised 

 rocks has already been dealt with (pp. 35, 162, etc.), but it cannot be too strongly emphasised 

 that the formation of this sandstone can only take place on the beach and between tide-marks. 

 Its constituents show all the characteristics of such a formation, being much broken, angles 

 rounded and surfaces pitted. Among them may be recognised pieces of coral of all the kinds 

 found on the reefs or in the raised rock, but branching species especially of the genus Pocillopora 

 are by far the most abundant. Small Molluscan shells and fragments of shell are common. Bits 

 of nullipore, leaves of Halimeda and similar algae, spines and ossifications of Echinoderms, 

 Crustacean remains and shells of Foraminifera make up the residue. The only constituents, 

 not of lime formation, sometimes found are more or less decomposed fragments of pumice and 

 sponge spicules and remains, but all these are relatively scarce, and do not in the Maldives 

 form together more than '1 per cent, of the total analysis. For the constitution of the rock, 

 however, its mode of formation and its method of occurrence may best be considered. 



The sand rock presents in its typical development on any beach a series of sloping 

 terraces, separated from one another by steps. These terraces slope at the angle of the dip 

 of the beach or slightly less, and the step from one to the other is about 5 inches and extends 



1 Vide "The Geology of Rotuma," Q. J. Geo. Soc. vol. liv. pp. 1—11 (1898) and "The Coral Reefs of Funafuti, 

 Rotuma, etc." loc. cit. pp. 438 — 44 (1898). 



G. 44 



