Volcano Oshima, Idzu. 49 



of the outer slopes of the somma is normal in this part and the 

 layers of éjecta covering the solid lavas are comparatively thin. 



On the southeadern flank, as the original relief is complicated 

 owing to specially frequent volcanic actions on this side (p. 26), 

 the development of the valleys is accordingly irregular. Moreover, 

 as easily dissectible scoriaceous éjecta constitute the ground in 

 this part, temporary streams have excavated it deeply. 



The eastern slope of the volcano, continuing from the inside 

 of the caldora toward the east coast through the great north- 

 eastern gap of the ring- wall of the somma, is thickly covered by 

 loose sandy materials. There the ground is almost undissected. 

 This is due to the constant levelling action of the western wind 

 in shifting the loose materials. 



The part along the east coast of the island is deeply dissect- 

 ed, valleys being sometimes as deep as 200 m. These apparently 

 incomprehensible sculptures may be well understood when the 

 drainage in Oshima is considered. The water that falls hi the 

 Ciddera, after soaking down through the sands and lapilli, by 

 which the inside of the caldera is loosely covered, till the surface 

 of the underlying lava is reached, runs off the natural slopes ; 

 accordingly a larger quantity of water is supplied to the eastern 

 part of the island than to any other, since the ring- wall of the 

 somma is greatly broken on the eastern side and the running 

 down of temporary streams is uninterrupted. Moreover, the slope 

 of the ground is especially steep near the east coast. Both of 

 these conditions would naturally favour a greater dissection here. 



(Ill) 2lie Coast. 



The island is constantly subjected to marine erosion at its 

 margins. The waves that dash against the shore break up and 



