270 



Y. OINOUYE 



to the size of the cone, the thicker laminae being found in the larger 

 cones. As is usual with all the cones of this region, it was cold 

 water that issued from them before the eruption of the volcano. 



On the north side of Usu a few cones were found on the flat farm 

 land at the foot of the mountain. At no other place in the neigh- 

 borhood were these phenomena observed. All the cones were 



Fig. 14. — Step fault at the west foot of Kompirayama. Taken August 18, 1910 



formed by the first severe earthquake, which occurred at 4:30 p.m. 

 on July 24, 1910. The phenomenon is not a peculiar one, for such 

 cones have been reported at many places where strong earthquakes 

 have taken place. They are invariably located along the crack 

 formed by the earthquake where the ground- water issuing through 

 the newly opened vent brings sand and mud with it to the surface. 

 After the eruption of the volcano the mud cones ceased to be 

 active and were gradually obliterated by the process of erosion. 



4. Rise of the water-level in near-by wells. — Practically all the 

 wells in the neighborhood of the volcano showed a rise in the 



