Volcano Üshima, Idzu. 133 



middle Tertiary and lasted toward the end, with repeated renewal 

 and decay in activity. 



How these rocks are magmatically related to one another is 

 a matter needing further investigation, yet it seems but natural to 

 consider them as of two distinct hneages— rhyolitic and andesitic. 

 It is to be noted that ike rocks of these two Uncages erupted 

 -alternatehj in the Idzu peninsula In the Tertiary period. 



This order of eruption of these two rock-types being very 

 important, the writer made a special point of confirming it during 

 his trip. Tlie youngest pyroxene -andésite covering the other rocks 

 is seen in almost every part of the peninsula. There is, besides 

 this, an older pyroxene-andesite underlying a liparitic rock. This 

 older andésite was included by Kôzu in his " propylite " though 

 the rock is, as he himself says, sometimes quite fresh. The age 

 relation of this older andésite to a liparitic rock was observed by 

 the present writer at two localities : near Nagata^\ a small village 

 4 km. (or 1 ri) northeast of Shimoda, where a liparitic tuff bed 

 •containing blocks of pyroxene-andesite was seen; and at the 

 boundary of Asahi-mura^^ and Chikuma-mmu^\ on the north side 

 of the main road that runs westward from Shimoda through 

 Kisami^\ where an altered andesitic rock is overlain by a bed of 

 hparitic tuff some 4 m. thick. 



Of the andesitic and rhyolitic rocks, the former continued to 

 extrude in the Quaternary period in the Idzu peninsula and its 

 environs. The Quaternary volcanoes, Amagi, Ashitaka, Fuji, Atami, 

 nakone'''\ etc., are all built up of rocks belonging to the andesitic 

 lineage which are considered to have descended from the Tertiary 

 andesitic rocks of the southern part of the Idzu peninsula. 



As a whole, the nature of the lavas of these volcanoes appears 



