Volcano Ushima, Idzi^. 201 



but similar double refraction to the afore- mentioned plagioelase, and 

 show a micrographie fabric. 



Of the many kinds of phanerocrystalline blocks found in the 

 Tolcanoes of Japan, one somewhat similar to that described hero 

 was discovered by Hirabayashi'-' among the éjecta of FiijP, being 

 especially abundant around the crater of one of its parasitic cones, 

 Hôeizan.'-' It consists of anorthite, augite, hypersthene, and 

 magnetite. He considered it as a fragmented block of a deep- 

 seated dyke since a rock with similar pétrographie characters was 

 actually observed occurring as a dyk:' in the highly dissected 

 Ashitaka^^ an older volcano adjacent to Fuji. 



The genesis of our micro-diorite will be discussed on pp. 

 121-125. 



V. History of the Magma. 



A 



In the foregoing pages, the various rock -types of Oshima have 

 been described in detail. Each of these rock-types has certain 

 ■distinguishing characteristics, but all of them differ only slightly fi-om 

 one another, agreeing so closely in their essential features that they 

 are considered to have originated from the same magma. Wh^it, 

 then, is this original magma ? How have the various rock-types 

 and the pétrographie characters as now seen been developed from 

 it ? The present chapter is an attempt to answer these questions 



A 



and to discuss the history of the magma of Oshima. 



The more important rock- types, except those occurring as 

 dykes and éjecta, are : — 



1) " Volcanoes Fuji and Ashitaka," J^eport Earthq. Invest. Com., 'So. 24, 1899 (in Jai>anese). 



3) K*ll| 



4) ^m 



