ANDREWS: LIMESTONES OF THE FIJI ISLANDS. 39 
line of volcanic vents, while its north and south extremities consist of 
lofty limestone escarpments. Silicified corals lie on the summits of the 
razorbacks and higher slopes of Vanua Mbalavu, and are evidently 
examples of silicification by contact metamorphism through percola- 
tion into reef coral of superheated water derived from the volcanic 
rocks. 
At Mango and Thithia similar silicification may be noticed. 
On Mango, a spring draining the north side of a volcanic mass 600 
feet in height suddenly disappears in an enormous mass of limestone. 
This point of disappearance is at the 50 feet level above high-water 
mark, but almost immediately above this another andesite mass rises 
seawards to a height of 150 feet above the sea in such a position that it 
is interposed between the point of disappearance of the stream and the 
sea-shore. The distance thence to the cuast is 500 yards; the stream, 
which is of considerable volume, reappears on the beach 600 yards away. 
It is far more probable that the water worked its way through a lime- 
stone substratum than that it percolated through the more or less imper- 
vious andesite. If this is so, the volcanic rock must here be above and 
newer than the limestone. 
At the south of Vanua Mbalavu a hot spring bubbles up through the 
limestone near the tidal zone. The temperature, though below boiling- 
point, is high enough to scald the skin. At times the water in the ad- 
jacent lagoon becomes heated over a small area. About 30 yards distant 
from the first spring, another hot spring occurs in the midst of a lime- 
stone fissure. 
Both these springs are in close proximity to the junction line between 
what, in my opinion, is one of the latest intrusions of andesite and the 
old reef rock. 
At Naitamba, Tuvuth4, and Kambara! the old lagoon floors are still 
intact.? Mango and Thithia were doubtless once possessed of similar 
lagoon hollows prior to the great covering of volcanic alluvium which 
now hides the old limestone floor. Consequently, if this reasoning is 
right, these lagoons antedate the chief volcanic outbursts. 
Calcareous deposits obscure everything along the coasts of Lau with 
the exception of the volcanic rock, whether in dome-shape, dyke-form, 
or as tuffs. The enormous rolling hills of andesitic lava that have spread 
out from the cliffs have no trace of limestone or calcareous material at- 
tached to their sides, except at Kambara, where whitened, burnt blocks 
1 See A. Agassiz, J. c., p. 74. 
2 At Kambara certainly not. — A. AGAssiz. 
