Benson.—Structural Features of the Margin of Australasia. 121 
northern and eastern portion of the Solomon Islands, Florida, Ysabel, 
Choiseul, Bougainville, Вака, and thence along the volcanic islands of the 
Namatanai chain a short distance east and north of New Ireland and 
New Hanover, and terminating in St. Matthias Island (Mussau) ; while 
cordilleran nature of the Namatanai ridge is shown by the occurrence of 
diorite i і s. 
In regard to the structure of the Solomon Islands, little can be added 
here to Suess's (1909) account of this group. According to Stanley (1923), 
the latest phase of volcanic activity is represented in Buka and Bougainville 
Islands; and in Poperang, a small island immediately south of the latter, 
there is a grey crystalline limestone containing Rhynchonella, which Suess 
thinks may possibly be Mesozoic. In Ysabel, diallage-serpentine is known, 
and schistose serpentine and granulite in Florida Island. In Gaudalcanar, 
andesite, dolerite, and porphyry occur, besides Recent volcanic rocks, 
peridotite, gabbro, serpentine, and a grey slickensided (possibly Mesozoic) 
limestone. San Christoval is very clearly a: portion of an ancient 
uniform « 
(cf. Guppy, 1887). 
The arc of the Solomon Islands is separated by a deep transverse 
depression from that of the New Hebrides. Mawson (1905) was unable 
by the outpouring of basalt and the formation of unfolded Pliocene and 
