GEOLOGICAL OBSKRVATIONS IN FIJL 117 



Its f)osition in the norm classification is: — 



Class III Dosalane, 



Order o Gernianare, 



Rang 4 Hessase, 



Subrang 3 Hessose. 



b. Ba^'alt. Porphyritic basalts are found througiiout the Lambasa 

 valley. They overlie the gabbro just described and form agglomer- 

 ates composing the bulk of the peaks of the Three Sisters and Mount 

 Avuka. The specimen to be described was taken from a limestone- 

 covered ridge, jutting out into the delta'plain a mile and a half north- 

 west of Laml)asa. 



Phenocrysts of diallage are associated with more abundant pheno- 

 crysts of plagioclase (Ab6oAn4o, to AbioAneo) in the rock. Due to 

 decomposition, epidote is abundant in the ground-mass associated 

 with feldspar and augite. Magnetite dust is also present in large 

 amount. The structure of the ground-mass is diabasic. 



The feldspars are zoned, but difficult to determine because of decay. 

 The average feldspar approaches a basic andesine and hence the rock 

 in places verges into basaltic andesites. 



c. Foraminiferal Basaltic Ash. A number of hills rising to an 

 elevation of approximately 160 feet dot the Lambasa flood plain. 

 They are composed of fine, greenish ash of basaltic composition, 

 doubtless allied in origin with the basalt of the adjacent hills. 



The ash is well cemented into a compact, greenish-gray rock of 

 very fine texture. The grain is, however, coarser than that of the 

 marls of the Suva district. Foraminiferal tests indicate that the 

 deposit was laid down beneath the sea. 



d. Andesitic Porphyrite and Piichstonc. The shore east of the 

 ]Mbutha Sau river, near Lambasa, is composed of a fine, grayish white, 

 rhyolitic ash. The ash is occasionally intruded by slightly vesicular, 

 porphyritic dikes, having pitchstone contact-facies against the rhyo- 

 lite. The dike rock described below occurs on Salia Levu Point, near 

 Wavu Wavu. 



The rock is slate-gray in color, massive, and shows an occasional 

 minute feldspar in an aphanitic ground-mass. 



The feldspar phenocrysts have the composition, oligoclase-andesine, 

 (AbroAnao) , and the ground-mass is composed of feldspar and glass with 

 a hyalopilitic texture. 



