INTERESTING PHENOMENA ON THE ERUPTION OF USU 269 



numerous small parallel fault fractures besides showing 2 m. of 

 horizontal shifting (Figs. 7 and 8). 



3. Mud cones. — The mud cones are small mounds of mud and 

 sand, well stratified and laminated. They range in size from 

 several centimeters to three meters in diameter, and are flat and 

 conical in shape, the angle of slope being from 3 to 16 degrees. 

 The smallest cone seen measured 10 cm. in diameter, and the largest 



Fig. 13. — North scarp of "graben" at the top of Kompirayama. Taken July 14, 

 ion. 



5 m. (Fig. 5). The height of the former was 3 cm. and that of the 

 latter 60 cm. Great numbers of such cones were formed in the 

 bay at the southwestern foot of the mountain, distributed irregu- 

 larly upon the tidal flat (Fig. 6). About 200 m. from the shore 

 line there is a row of such cones trending generally northwest- 

 southeast. While this row of cones is roughly parallel to the shore 

 line, and consequently fairly straight, there are numerous bends in 

 the line. From the structure of the cones it follows that there must 

 have been a periodical eruption of the sand and mud. The lamina- 

 tions, ranging from 5 mm. up to 3 or 4 cm., are roughly proportional 



