= BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
with ferric oxide. A small hole exists near the present sea-level in 
the limestone, and by crawling in one finds a small cave about 8 feet 
long and 3 feet wide. The sides are composed of red volcanic clay 
most distinctly bedded. Above this is found a reddish, hard lime- 
stone, and a very short distance away the coral rock itself occurs. Hot 
springs also exist throughout this limestone area. 
Mango. — On the summit of a typically shaped andesite dome, and 
carried to its present position by the eruption of this same lava mass, 
a massive bedded limestone occurs (Plate 2, Fig. 1). It overlays a 
greatly decomposed volcanic conglomerate, gray to greenish in color. A 
number of gasteropods are scattered throughout the mass of the con- 
glomerate. The stratified beds immediately above the decayed vol- 
canic material are a dense, compact, reddish limestone, with fragments 
of fossils in places. It is very similar to the basal limestone at Mba Vatu 
and Malatta. 
The bulk of this volcanic conglomerate cannot lie at a depth much 
below sea-level, if, as seems probable, its thickness is comparable with 
that of the outlier shown on the left hand of the section of Mango given 
on Plate 2, Fig. 1, which has been pushed up into its present position 
by an outburst of andesite.1 We can easily avoid the necessity for ex- 
plaining away huge deposits of coral reef origin, since the overlying reef 
material occupied but a fairly thin crust. 
Tuvuthd is as instructive as Mango. An old volcanic conglomerate 
almost identical in appearance with that seen on Mango occurs on the 
sea beach. A newer andesite lava has broken through and poured over 
it and also towards the limestone cliffs, leaving a gap between the two. 
Geological History of the Lau Group and its relations to 
the Western Fiji Islands. 
It is now possible to suggest the general lines along which the present 
features of Lau were developed. Calcareous deposits, which afterwards 
formed the “bedded” limestones, were laid down on the floor of the 
ocean, the submarine plain which later was to form the foundation of 
the Lau Group. The existence of a basal volcanic conglomerate below 
the reef rock at Mango and Tuvutha shows that there succeeded a period 
1 This does not imply that compact basal limestones project above the floor of 
the central hollow, but that the undisturbed and the disrupted rock are similar in 
their upper portions. 
