Notes on brown hornblende and biotite from Shabō-zan, of the Dalton volcanoes, Taiwan, Japan

Abstract

The Dalton volcanoes include all the volcanic groups which rise up at the north-western end of Taiwan (Formosa). They are old extinct volcanoes underlain by highly disturbed Tertiary sediments. Among them Shichisei-zan is the highest and the most prominent, rising up to 1108.7 metres above sea-level. It is mostly made up of hornb]ende-andesite, hypersthene-hornblende-andesite, and agglomerates. On the western slope of this partly dissected volcano there is a very characteristic cone called Shabō-zan. Its elevation is 643 metres above sea-level, and it is mostly made up of hypersthenehornblende- andesite poured out through the thick accumulation of agglomerates. The andesite here has usually a grey colour, but often passes into a light reddish-brown variety, being sometimes associated with a noritic segregation mass. It is noteworthy that some of the andesites abundantly contain brown hornblende. This mineral also frequently appears, together with brown biotite, in the segregation mass.