ANDREWS: LIMESTONES OF THE FIJI ISLANDS. 33 
of volcanism, probably in Tertiary time, during which masses of volcanic 
material were heaped up along a fairly well-marked north and south line 
of weakness. The highest of these masses of volcanic rock, such as 
Yathata, Tuvuthé, and Vatu Vara, came within the reef-building zone 
of corals, and reefs commenced to form upon them. Alternating epochs 
of upheaval and stable equilibrium followed, during which the reefs grew 
outwards over calcareous banks as well as the bedded limestone. This 
is demonstrated by the long lines of erosion cut into the cliffs of Lau 
and the sub-horizontal terraces above them. This state of unrest must 
have continued, for a long period of time, to have produced the vast 
masses of limestone like those of Mango and Tuvutha. 
Another volcanic phase occurred in recent time. The andesite out- 
bursts, which disrupted the old reef rock and bedded limestones, formed 
the coarse agglomerates with large included lumps of coral, and capped 
the latter with domes of lava. Many of the limestone islands became 
centres of eruption. At first numerous explosion craters were formed, 
and blocks of andesite and reef limestone were hurled from the vents 
until large islands were piled up by the ejectamenta. The former island 
of Vanua Mbalavu was almost completely wrecked as a result of the 
volcanic explosions. 
Another instructive feature in these outbursts’ is the fact that the 
bases of the great limestone cliffs became in many places the centres of 
disturbance. If the eruption was extensive, then the clitf vanished and 
a heap of calcareous agglomerate was all that was left to attest to its 
former existence. If the disturbance was smaller, then the volcanic 
matter welled up from the cliff base without wholesale fracturing of the 
limestone. 
Subsequent to, or perhaps immediately after the first paroxysmal out- 
bursts, the andesites welled up in dome-shaped form and buried the coral 
agglomerates, produced by the earlier explosions, as well as the surround- 
ing limestone. A final phase in the eruptions is marked by the later 
eruptions of olivine basalts. These found vents at the bases of the older 
andesite domes, and at Mango are represented by small tongue-shaped 
flows and minor masses. 
From these fragmentary traces of basal rocks and from these indubi- 
table signs of elevation, it is possible to understand the mode of formation 
of the Lau limestones and their subsequent elevation. Along the sub- 
marine plateau and running a little west and east of a meridional line, 
volcanic masses were erupted along the axis of regional elevation ; and 
on these as a base great accumulations of volcanic ash and conglomerates 
VOL. XxXxXvIII. — No. l. 3 
