694 



NOTE ON SOME RECENT WORK ON THE ROCKS 

 OF SAMOA. 



By H. I. Jensen, D.Sc. 



I have recently received from Professor M. Weber, of Munich, 

 an exhaustive report on the petrography of the Samoan Islands, 

 worked oat from a collection of rocks made by Herr J. 

 Friedlander in 1907.* The report is, to me, of extreme interest, 

 since it casts further light on two problems already discussed in 

 m}^ papers. 



In my chemical note on a recently erupted hyalopilitic basalt 

 from Savaii f my analysis showed a higher soda-content than 

 might have been expected from the petrological description. I 

 explained that this was probably due to the existence of an 

 alkaline matrix in the glassy base, and to a high alkali-content 

 in the greenish-brown augite. Professor Weber has examined a 

 specimen of the same lava and has also found the felspar to be 

 hytownite. He has not analysed this specimen, but in his other 

 analyses of older Savaiian lavas he finds, as I did, that their 

 titanium-contents are remarkably high; and he also finds that 

 many of them approach, both mineralogically and chemically, 

 to the alkaline division of igneous rocks. My own researches 

 were confined to those specimens which I collected near the active 

 volcano, and near Apia in Upolo; hence I failed to discover any 

 rocks of a distinctly c^/^"aZi/ie/ac^es. The rocks described by Professor 

 Weber include felspar-basalts, palagonite-tuff, phonolite,nepheline- 

 basanite; and, from the island of Tutuila, which I did not visit, 

 he describes alkali-trachyte, and phonolitic trachyte as well. 



* Weber, M., " Zur Petrographie der Samoa-Inseln," Abh. d. ii. Kl. K. 

 Bay. Akad. d. Wiss. zu Munchen. xxiv. 287, 1909. 



t These Proceedings, 1907, p. 706. 



