470 
GEOLOGY: W. M. DAVIS 
reef, then uplifted 450 feet, and again fringed at present sea level; its 
highest summits now rise 650 feet above the sea. Vatu Vara is a former 
atoll, presumably formed during subsidence, but now standing 1030 feet 
above sea level and nearly 2 miles in diameter at its base; it is the 
highest elevated reef in Fiji. According to Andrews its steep slopes are 
contoured above and below mid-height by two corniced ^'water-lines;" 
hence its uplift must have been recent and rapid: like Mango, it is now 
fringed by a sea-level reef. Frost reef is a mile in diameter: it has no 
lagoon. Soundings of 103, 115, 134, 146, and 133 fathoms are charted 
at less than half a mile away; 200 fathoms and no bottom are recorded 
at three points toward Mango. If Frost reef be diminished by re- 
moving a fringe of somewhat less than the average sea-level fringe- 
width now surrounding Mango or Vatu Vara, it will be reduced to a 
mere point; and as such it was probably extinguished while Mango and 
Vatu Vara were subsiding; it must eventually have been submerged 
FIG. 3. 
under more than 100 fathoms of water, when the highest reefs of 
Mango and Vatu Vara were at sea level, ss; but it was revealed as a 
resurgent reef when the following uplift brought sea level to EE. 
Midway in the eight-mile passage between the great barrier reef of 
the Exploring Isles, B, and Kimbombo reef, K, on the north is Trigger 
rock, T, figure 3, a minute reef in four fathoms of water, with the 100- 
fathom circle hardly half a mile in diameter, and soundings of 110, 121, 
154 and 136 fathoms close outside. This rock must have been ex- 
tinguished during the subsidence in which the now-elevated limestones 
of the Exploring Isles and Kimbombo were accumulating, and then 
submerged to a depth of 100 fathoms or more when the highest lime- 
stones were formed at the level ss; but a later upheaval brought it to 
light again as a resurgent reef, with sea level at tt; then it may have 
been recolonized for a time while the neighboring elevated limestones 
were suffering dissection; now, since the dissected limestones have 
again subsided, so that sea level is EE, the reef is almost extinguished 
