GEOLOGIC STRUCTURE OF THE EIUKIÜ CURVE. g 



Lutmria (?), Gardiwn (?) and EcMiiodùcus. According to Richthofen, 

 trachyte with its tuff and agglomerate, is found in the north-east and 

 south-west of Köbi, near Daiton-zan and Kwannon-zan ; and compo- 

 ses the foundation of the environs of Köbi. Here a C[uite horizontal 

 tuff predomates and forms the vast plateau ontlie south-west of Köbi. 

 Porphyrite hills are found, according to 'i'yzack, at Daiton-zan and 

 Kiirun-zan. 



The more careful geological observations and microscopic studies 

 by Japanese geologists, show these inferences to have been mostly 

 incorrect. The igneous rocks of Daiton-zan, Kwannon-zan, Kiirun- 

 zan and others, are proved to be not trachyte but andésite; and there 

 has been found no trachyte tuft*. The rocks of the vast plateau near 

 Köbi is nothing else than latérite. 



Mr. Y. Ishii published in 1897 a reconnuisance map of Formosa 

 with an explanatory text in Japanese.* Except the doubtful occurrence 

 of gneiss, he found all the oldest rock to be crystalline schists, extending 

 from the eastern side of Mount Sylvia up to the north-west of Pinan. 

 A crystalline limestone, probably Palaeozoic, is observed along the 

 western side of this schistose belt, and extends from the east of Sessan 

 to the north-west of Pinan. A clay slate of unknown age occupies a 

 very wide area, between Toi, north of Giran, and Böryö near the 

 southern end of Formosa. The main skeleton of the island, thus 

 formed by the schists, limestone and clay slate, has been called the 

 " Taiwan mountain system " by Mr. Ishii. The clay slate seems to 

 surround the region of schists and limestone. The Tertiary sediments 

 which overlie the clay slate without any discordance, are developed 

 along the northern, western and southern sides of the principal ninge, 

 as well as the middle of the eastern coast. Those in the northern part 



fâ^K^;É^itM^ (Explanatory Text to the Map of Formosa, showing Geology and 

 Mineral Kesources). 



