68 



Y. KIKUCHI 



pinnacles and ridges, due to the extrusion of the harder rock- 

 masses by erosion. The most prominent of these ridges rises 

 about 1100 ft. above sea-level. 



The volcanic rocks are chiefly Andésite ; sometimes in a mas- 

 sive state, occasionally showing prismatic joints ; sometimes interstra- 

 tified with tuffs. These tuffs usually contain fragments of volcanic 

 rock, of various sizes, forming agglomerates. The volcanic rocks 

 are generally much altered, and as the product of alteration, we find 

 secretions of Chalcedony, Calcite, and Zeolite among the fissures. 

 This is especially the case among the more basic glassy varieties, the 

 characteristics of which will be given briefly in this place. They 

 are also much decomposed at the surface into a peculiar reddish soil 

 resembling Latérite. 



In the first account relating to the geoloo'v of the island, found 

 in the narrative of the famous American Expedition under Commodore 

 Perry,* it is stated (Vol. I, p. 202) ''The geological formation of the 

 island is trappean, with its various configurations and mineralogical 

 peculiarities ; columnar basalt appears, and hornblende and chalcedony 

 are found." The 'hornblende' mentioned in the above citation most 

 probably refers to the crystallized Rhombic Pyroxene here to be 

 described. This mineral therefore seems to have attracted the atten- 

 tion of early observers. Also in some Japanese book, treating of the 

 products of the island, we find its crystal-form figured and mentioned 

 as Olivine, and stated as also occurring in Kitajima, a small island 

 to the north of Ototojima. 



In the summer of 1884, Mr. T. Suzuki of the Geological Survey 

 visited Chichijima, and made a collection of rocks, an account 



* Narrative of the Expedition of an American Squadron to the China Seas and Japan 

 performed in the years 1852, 1853, and 1854, under the command of Commodore Perry, com- 

 piled by F, L. Hawks. 3 vol. 1 Atlas. Washington 1856. 



