ON ANORTHITE FROM MIYAKEJIMA. 33 



Generally a brown coloured glass basis is found between these crystals. 

 Anorthite, Olivine, and Augite CiMistitiite the essential microscopic 

 porphyritic components. The order of crystalliziition of these com- 

 ponents can pretty certainly be described as follows: — Aj^atite, 

 Magnetite, Olivine, Anorthite, and Augite. A specimen of Basalt- 

 glass or Tachylite is also known. Under the microscope, it is found 

 to consist of a brown glass, in which well-defined crystals of Anor- 

 thite, Augite-microliths, Olivine and Magnetite are developed. The 

 recent lava of Miyake may therefore be called Anorthite-basalt. 



The volcanic rock composing the upper part of Fujiyama is, 

 according to Lüdecke and AYada,* Anorthite-basalt. It is probable 

 that this rock constitutes most of the lavas of comparatively recent 

 eruptions in the volcanoes of the Shicliitö Group. The chemical 

 analysis of the Anorthite forming the porphyritic component of the 

 rock f(jund near Tönosawa, situated within the extinct volcano of 

 Hakone, was first published by Wada.* But unfortunately the 

 crystaîlographic and optical characters could not be well investigated 

 because of the nature of these crystals. Certain glassy Felspar crystals 

 which had been brought from the Island of Oshima and known as 

 Saiiidine, were found on examination to be completely identical with 

 the specimens from Miyake. Dr. E. Xaumannt states in his account 

 of the Island of Oshima, that Sanidine crystals occur very abundantly 

 in the lava of that Island. So far, however, I have been unable to 

 find anv Sanidine crystal in anv of the collections brouofht from 

 Oshima, which have been to mv hand. 



The Anorthite-crystals from Miyakejima are 1 - 4om. in their 

 longest direction, and are always covered with a black or sometimes 



* Notas ou FujiyaniA — Transactions of the Seism. Soc. of Japan. Vol. IV 1882. 

 t Die Vulkauinssl Ooshima u. ihre jüngste Eruption — Zeitschft. d. deutsch, geol. Geseiht. 

 Bd. 29. 1877. p. 378. 



