ANDREWS: LIMESTONES OF THE FIJI ISLANDS. 39 



line of volcanic vents, while its north and south extremities consist of 

 lofty limestone escarpments. Silicihed corals lie on the summits of the 

 razorbacks and higher slopes of Vanua Mbalavu, and are evidently 

 examples of silicihcation by contact metamorphism through percola- 

 tion into reef coral of superheated water derived from the volcanic 

 rocks. 



At Mango and Thithia similar silicihcation 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 coast is 500 yards ; the stream, 

 which is of considerable volume, reappears on the beach 600 yards away. 

 It is far mere 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, Tuvutha, and Kambara 1 the old lagoon floors are still 

 intact. 2 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, /. c, p. 74. 



2 At Kambara certainly not. — A Agassi*. 



