44 Vol. XLIIL, Art. 6. — S. Tsuboi : 



supposed to have direct connection with the main magma reser- 

 voir, it is difficult to explain why they expired so soon in view 

 of the high probability of a constant action of " gas-flnxing " or 

 " blow-piping." 



Explanation of the Present Features. 



The topography is the end product of structure, process, and 

 stage, as Davis says, and all the present features of Oshima are 

 well explained when they are considered to be the combined results 

 of tlie structure of the volcano and the agencies at work on it. 

 The surficial agencies that are believed to have been acting on 

 the island are winds, temporary streams caused by cloudbursts, 

 and sea waves. No doubt these agencies must have been operat- 

 ing at every stage of the development of the insular volcano 

 since it came into existence. But, on the other hand, repeated 

 volcanic eruptions depositing juvenile products have covered the 

 effects cf these surficial agencies, whereupon the agencies have 

 begun to act anew. Thus the surficial agencies have not yet had 

 a sufficient opportunity to modify greatly the original topographic 

 features depondent on the structure. In the following, an ex- 

 planation for the more remarkable topographic features will be 

 given : — 



(I) Jlie Developmeni of the Mountain Slopes. 



The development of the mountain slopes of Oshima is not 

 uniform in all directions. 



(1) The loestern flank of the somma is very regularly de- 

 veloped showing a gradual slope with decreasing inclination down- 

 wards. This may be because no conditions have obstructed the 

 natui-al development of the mountain slope in this part. 



