50 FOYE. 



contact was found between tuff and limestone; yet because the tuff 

 deposits underlie the limestone and rise into it in a series of irregular 

 domes, it is inferred that the history of the island must be as stated. 

 Besides, the pyritization of the tuff must have occurred before the 

 deposition of the limestone, since the latter rock is not pyritized. 



Dips of 10° to 14° were seen in the limestones, but, since the lime- 

 stones of the other islands rise to a uniform level, it is believed they 

 have not been tilted, but rather were deposited at this angle. The 

 same argument holds good for similar irregularities of dip indicated 

 on the map of Vanua Mbalavu. 



On the southern side of Avea, coral heads in place were found in 

 small, secluded inlets along the precipitous coast. These heads are 

 conformably overlain by coralliferous limestone. They are surrounded 

 by a paste of coral and shell rubble, as in the present-day reefs. The 

 coral heads indicate that a considerable subsidence must have fol- 

 lowed their growth. 



• Yanu Yanu. The relation of the tuft's to the andesites is not clear 

 from the occurrence at Avea, but is revealed by a study of Yanu 

 Yanu, (see Figure 20). This island is almond-shaped with a sand 

 point extending westward. The island is less than a mile in length 

 and is cone-shaped. Its northeastern side is formed of tuft', visible 

 in a cliff 40 to 50 feet in height. The original form of the deposit has 

 been lost through profound erosion. It now covers an area of less 

 than an acre. To the south the ash is intruded by an acid andesite, 

 which cuts off its further extension in that direction. To the west, the 

 main mass of the island, rising in a cone to an elevation of 270 feet, 

 is composed of an olivine basalt of the second volcanic period, which 

 intrudes and overflows the ash. The presence of these later rocks, 

 surrounding the very loose and easily eroded ash, accounts for the 

 preservation of the latter. 



Malatta. The islands of Malatta and Susui, adjacent to Vanua 

 Mbalavu, represent a continuation of the limestone mass forming the 

 southern end of Vanua Mbalavu. This limestone mass has been 

 separated into the three islands by the process of solution and outward 

 drainage outlined abo^'e. The process is still continuing and the 

 islands will undergo further dismemberment. 



Malatta averages about 200 feet in height. Its interior is so 

 roughened with solution pits that the island is practicafty impassable. 

 About its shore-line, precipitous cliff's, 40 to 50 feet high, render land- 

 ing from a boat very difficult. These clifts break down only near the 

 strait separating the island from Vanua Mbalavu. Just east of the 



