'PUFF" CONES ON MOUNT USU 



585 



the eruption the surface of the flow was so hard that it was difficult 

 to discern footprints upon it, and specimens could be obtained 

 only with the aid of a pointed stick or a hammer. At this time the 

 surface was flat except for low, wavy undulations and very irregular 

 sun cracks. 



A year later the writer found the flow covered with thousands 

 of small cones, each of which had an opening which was compara- 



OiaUtUii 



Fig. 2. — Map of Mt. Usu and vicinity, showing the position of craterlets and mud 

 flow here described. 



tively large but of no particular shape. The cones were of different 

 sizes, the smallest being o . 5 meter in diameter and o . 1 meter 

 in height while the largest was 3 . o meters in diameter and 1 . 5 

 meters in height. They were irregularly arranged on the flow 

 at intervals of 10 to 30 meters, and were either dome-shaped or 

 resembled a common bell with a slope of forty degrees. 



The cause which produced these elevations is the same as that 

 which forms small pitted cones when any viscous substance is 

 boiled, namely, the escape of gases or vapors through the mass 



