Vol. 54.] ME. J. S. GAKDINER ON THE GEOLOGY OF ROTUMA, 5 



the top about 240 feet deep, and an external slope of 50° to 60° 

 near the summit ; there are also craters on the summits of Atja 

 and Hoi, and Matja is simply a crater with one side blown out. 



Generally the rock is the same as on Satarua, a very vesicular 

 Java (see Appendix, p. 10, No. 2) ; but at the bases of Hoi, E,au, 

 Matja, and Vavasse, near the sea, a much finer-grained basalt 

 (loc. cit. No. 3) is found. 



At Oinafa, Noatau, Pepji, and many places along the coast the 

 volcanic rock is shut off from the sea by the formation of a sand- 

 flat, which also to some extent is found at the mouth of the 

 U-shaped range of hills. At Noatau in places it is | to ^ 

 mile broad, and is about 1 foot above high-tide level. Between 

 it and the sea is a further small rise of 2 to 3 feet. Holes dug 

 in it in places to a depth of 6 to 12 feet give nothing but loose 

 sand with fragments of corals, shells, nullipores, etc. Towards the 

 sea, on the beach between extreme tide- marks, it ends with a 

 * beach-sandstone formation '" sloping down at an angle of from 

 6° to 12° to the sea, and showing corresponding stratification ; in 

 places, however, this beach-sandstone is much overlain with sand. 

 It can be and is used for gravestones, split off in blocks of any 

 dimensions, but the strata never run more than 4 to 7 inches in 

 thickness. Below the first layer thus removed is a second, which, 

 however, is never so firmly consolidated. It then becomes less firm 

 till in 3 or 4 feet loose sand and fragments of coral, nullipores, etc., as 

 on the flat, make their appearance. On the beach the projecting ends 

 of six or seven layers, like so many steps, may be seen. Used as 

 gravestones, exposed to the air and not acted on by the sea, it 

 hardens, becomes more compact, and rings to the hammer. After the 

 removal of a layer the under layer now exposed hardens consider- 

 ably, and the place of the old layer is taken up by the sand. The 

 part exposed to the air and waves is hardest, and where broken off 

 from the stratum is usually covered with sand. Here, however, it is 

 reformed, growing up under the covering sand, as it were, from the 

 broken edge. 



At Oinafa this sand-flat has a height at most parts of a few 

 inches above high tide, but 100 yards in from the coast, imme- 

 diately behind the anchorage, it descends to 1-3 feet below high- 

 tide level. This area is nearly half a mile long by 300 yards in 

 greatest breadth. In places in it are pools 6 to 7 feet deep, and much 

 of the remainder is taken up by a swamp, in which papoi or broka, 

 a species of arum, is cultivated for food. On it, more or less buried 

 in the sand, are loose blocks of coral strewed about, and a crowbar 

 cannot be forced down far without meeting solid rock, which is 

 usually of coral formation. Between it and the sea to the north-east, 

 the sand-beach is 3 to 4 feet above high tide, and the beach-sand 

 rock is unusually well defined. It seems really as if a small lagoon 

 in connexion with the sea had once existed here, but had been filled 

 up by corals, sand, etc., and cut off from the sea by the formation 

 to the north of a saud-beach. 



Somewhat similar but much smaller swamps exist in Noatau and 



