606 MR. J. J. LISTER ON THE GEOLOGY 



•wide opening, overarched by a natural bridge of the limestone 

 rock, the under surface of which is festooned with stalactites. The 

 sea entering beneath the arch washes the bases of the nearly vertical 

 sides of the chasm. The place is called by the natives Matalanga 

 Maui (or the hole made by the implement for planting yams belong- 

 ing to the god Maui). The manner in which the chasm has been 

 excavated appears obvious. At the foot of the cliffs there are 

 several caves in ditferent stages of excavation, which are formed by 

 the sea wearing back the volcanic rock where it is exposed beneath 

 the limestone. The Matalanga Maui has been formed by the 

 removal of the volcanic rock to such an extent that the cave has 

 approached the surface of the terrace and the roof has fallen in. 



I may here recapitulate the main features which seem to be 

 indicated by the structure of Eua. 



The presence of the plutonic rock points to the existence of an 

 ancient and much denuded mass of such a character in the vicinity. 



In the neighbourhood of this mass, and at a considerable depth 

 below the surface of the sea, a volcanic eruption occurred, forming 

 a mound, some of whose upper layers were mingled with pelagic 

 organisms as they were laid out. 



It appears that the mound Avas elevated above the surface, con- 

 siderably denuded, and afterwards depressed to such a depth, at 

 least, as to submerge its summit. 



A covering of calcareous organisms was deposited on the volcanic 

 basis while it was submerged ; but so far as the evidence goes the 

 formation is a shallow-water one. The island has since been again 

 elevated by stages to the present height. 



During periods when the elevatory forces were in abeyance, the 

 sea wore back the already emerged limestone-deposits, forming 

 terraces bounded by lines of cliff, but in one case at least (namel)', 

 the western terrace a) it appears that a true coral-reef was formed 

 in the neighbourhood of the shore. 



Dr. Murray finds that it is impossible to assign the organic 

 deposits of the island to a definite geological epoch. Though he is of 

 opinion that they are old, there is no satisfactory evidence to refer 

 them to the Tertiary period. 



(c) Islands formed entirely of Limestone. 



The islands forming the remarkable group of Vavau differ widely 

 in their shape and arrangement from coral islands in general. 



Yavau consists of one large island which gives its name to the 

 group, and of a number of smaller islets (see PL XXIII.). Yavau 

 Island presents a high and fairly even coast-line to the north and 

 north-east, bordered by limestone cliffs from 300 to 500 feet in 

 height. On the south and south-west the general lie of the laud is 

 lower than that on the noithern coast. Long promontories stretch 

 out from the main mass of the island, separated by narrow and deep 



