MAGMA TIC DIFFERENTIATION IN HAWAII 



3°7 



they would be more salic and alkalic than the parent basalt. As 

 a matter of fact, a goodly number of such derived magmas seem 

 to be represented in Hawaii. Table VIII, columns 2-6, shows the 

 chemistry of the principal types to which this mode of origin may 

 be, at least tentatively, ascribed. 



TABLE VIII 



tt Determined from hand-specimen collected by the writer. All three rocks for which specific 

 gravities are given, are holocrystalline. 



1 Average analysis of twenty basaltic types in Hawaii. 



2 Andesitic basalt of Mauna Kea. 



3 Trachydolerite of summit, Mauna Kea. 



4 "Andesite" (trachydolerite) of Waimea, Kohala district (analyzed by A. B. Lyons, Amer. Jour. 

 Scl, II [1896], 424). 



5 "Augite Andesite from the Sandwich Islands" (silica determined by E. Cohen, Neues Jahrbuch 

 fiir Mineralogie, etc. [1880; II, 38]). 



6 Phonolitic trachyte of Puu Anahulu (described by W. Cross, Journal of Geology, XII [1904], 510). 



On p. 53 of the paper by Cohen, for which the reference has 

 been given, it is stated that in the rock collection there described, 

 four other occurrences of "typical augite andesites" in Hawaii 

 are represented. Two of the specimens were taken on Mauna 

 Kea; the other two were collected on this island, but the labels 

 failed to give their exact localities. No analyses were made of 

 these specimens, but, of course, one may trust Cohen's well-known 

 skill in diagnosis and place all four rocks among the more salic 

 types of Hawaii. 



From the table it seems clear that the strongly alkaline trachyte 



