Vol. 54.] MR. J. S. GARDINER ON THE GEOLOGY OF ROTUMA. 7 



large pit leading into a number of passages and caves. South of 

 Mea is another such pit on a slight rise, called An Hufhuf (the Cave 

 of Many Bats) ; the detailed descriptions of both are appended. 



South of these are two hills, Sorou and Meamea, both of which 

 are of volcanic ash ; the former has, like Sororoa, a crater on the side 

 away from the sea. 



III. Caves, Pits, etc. 



On the summit of Mafiri (see figs. 1-4, p. 8) is a pit 13 to 14 feet 

 broad at the top and nearly circular in shape. Round the edge is 

 a raised rim 1 to 2 feet high and 6 inches thick, consisting of 

 much-weathered vesicular lava. Descending, the pit narrows to a 

 breadth of 5 feet at a depth of 32 feet, and then opens into an 

 immense chamber 70 feet long by 30 broad at the level of the 

 summit of a mound, which has formed in the centre 82 feet below 

 the mouth of the pit. The narrow pit to the depth of 32 feet has 

 the appearance of a wall, built up by man, of great rectangular 

 concave blocks of stone, owing to horizontal and vertical fractures. 

 The mound consists of loose masses of lava, earth, decaying vegetable 

 matter, etc., which have fallen in from the summit or the walls. 



On one side the mound slopes down, at an angle of 45°, for 

 60 feet or so into a small chamber, which is much filled np by 

 large fallen masses of rock. Twelve feet above one part of the 

 slope is a narrow triangular tunnel, about 3 feet high by the same 

 broad, running for 30 yards outward with a slight downward slope 

 of 1° to 3°. Near its end it opens into a chamber 16 feet high. Por 

 the last two-thirds of this tunnel the floor has a rough, black, some- 

 what ropy appearance, showing clearly the direction of a lava-flow 

 outward. On the roof hang a few small, sharp, conical stalactites, 

 never more than 2 or 3 inches long. At the end the roof and 

 floor approach each other at a very acute angle. 



On the other side of the mound the first slope is steeper, and runs 

 rather deeper down. It ends then in a tunnel about 110 yards 

 long, sloping down at an angle of 10° or less. Its general height is 

 about 6 feet in the centre, with a breadth of 12 to 15 feet. Its floor 

 is slightly higher in the centre, and shows for most of its course, 

 about i| feet from the walls, two cracks or fissures, 10 to 12 inches 

 deep by 3 or 4 broad at the top ; these follow very regularly its 

 course. N'ear its end it opens, as does the other tunnel, into a 

 large chamber, and the angle at its end is likewise very acute. The 

 structure of its walls, floor, and roof is the same as in the smaller 

 cave ; in no place, not even in the large chambers, is there any sign 

 of the walls or roof falling in in any way. The ropy appearance of 

 the floor, its raised centre and general trend, show conclusively the 

 direction of the flow of lava along the tunnel. Examining the 

 contour of the land above, there is a distinct rise, running out for a 

 considerable distance to the south-west, but signs of any direct 

 outflow from this tunnel or any difference of the lava could not be 

 detected. 



An Hufhuf seems to be directly comparable to Mafiri, only the 



