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REGINALD A. DALY 



water, as well as to the latest, violent expulsion of the juvenile 

 gases from the increasingly viscous magma. 



Little is known of the detailed geology of the Kohala district, 

 but the abundance of cinder-cones on the heights of this other 

 great pile suggest a differentiation history resembling that sketched 

 for Mauna Kea. However, the strongly alkaline "andesite" of 

 Waimea, like the phonolitic trachyte of Puu Anahulu, may repre- 

 sent limestone-fluxing as a leading condition for such specially 

 advanced differentiation of the basaltic magma. 



Parallel differentiation in other oceanic islands. — Weber's recent 

 study of the Samoan lavas, including those from Savaii, shows a 

 remarkable similarity between them and the rocks of the Hawaiian 

 group. 1 The types already found in Savaii and in the neighbor- 

 ing islands include: olivine basalt, olivine-poor basalt, andesitic 

 basalt, trachydolerite, " Alkali trachyt," trachyte, and phonolite. 

 " Savaii" is said to be the Samoan equivalent of the name "Hawaii." 

 By a curious coincidence the vent of Matavanu is, among vents 

 now active, the most perfect known analogue to Kilauea; and the 

 volcanic mechanism seems to be practically identical in these two 

 archipelagoes. The writer entirely agrees with Weber as to the 

 necessity of regarding the subalkaline and alkaline rocks of each 

 island group as syngenetic. The parallelism in the magmatic 

 histories of Savaii and Hawaii is shown even in details, for Weber 

 described olivine-augite nodules in the feldspar basalt of Mauga 

 Loa, a rock which in all respects recalls the nodule-bearing, ande- 

 sitic basalt of Mauna Kea. 



Among the leading effusive types in Tahiti are olivine basalt, 

 olivine-free basalt, hauynophyre, phonolite, and picrite, the 

 description of the last-mentioned rock resembling that of the ana- 

 lyzed 1852 flow in Hawaii. Although basalts compose most of 

 Tahiti, this mid-Pacific island has also furnished nephelite syenites, 

 theralites, essexitic gabbros, and tinguaites. 2 In the Solomon 

 islands olivine basalt and augite andesite are associated with an 



1 M. Weber, Abhandlungen Math-phys. Klasse, Kgl. Bayerischen Akademie der 

 Wissenschaften, XXIV (1909), 287. 



2 A. Lacroix, Bulletin Societe geologique France, X (1910), 91-124. 



