662 



GEOLOGY OF SAMOA AND THE ERUPTIONS IN SAVAII, 



Lister gives an excellent account of the terraced appearance 

 and geology of this island. He found inclusions of tourmaline- 

 bearing rock, and gabbro in the lavas of the island. He also calls 

 attention to the terracing of Vavau. I made an examination 

 of the interesting hill at Vavau, and found ffour distinct 

 levels represented on the island, (l)the summit of the hill 420 

 feet, (2) a 280 feet level, (3) the 160-180 feet level, and (4) a 40 

 feet level, evidencing at least four distinct uplifts. From the top 

 of the hill to sea-level, the hill is composed of coral limestone 

 containing coralline seaweeds (Nullipore, Lithothamnion), fora- 

 minifera (Miliolinida^, Orbitoides, and Rotalidse) and mollusca. 

 The limestone has a late Tertiary appearance. 



The oceanic depths near Tonga and the Kermadec Islands are 

 also of interest. East of these groups the greatest known depths 

 have been obtained, and there is, in fact, a long, very deep trough 

 running parallel to the volcanic line, between which and the 

 trough the shelf, on which the islands stand, is situated. West 



looo (eel 



Fig.6.— Sketch Section W.N.W.-E.S.E. across Tonga. 



of the volcanic belt the depth also suddenly increases. Con- 

 siderable depths are also known between the' several groups of 

 islands (see fig.6). 



The foregoing facts show that the volcanic belt from Lake 

 Taupo to Samoa is ranged along a great structural line in the 

 earth's crust, which possibly marks the eastern border of the 

 submerged Fijian continent. The deep trough eastward is 

 probably the depressed deep ocean which usually obtains near the 

 shores of continents, and may represent an old trough fault or 

 otherwise faulted area.* The volcanic line probably represents 



Of. Dana, " Characteristics of Volcanoes." Part 3. 



