144 



PROCEEDINGS OF THE AMHERST MEETING 



Additional evidence of viscosity of the lava at the time of the great erup- 

 tions, May 19 and 22, 1915, is furnished by some of the homhs ejected at that 

 time. No such homhs had been found in that region before the great eruption, 

 and the ones in question were certainly ejected during that eruption. The 

 bomb studied was slightly oblong-round and about three feet in diameter. It 

 was completely enveloped in a bread-crusted surface and when broken was 



Figure 2. — .Yc/r Lara from Lassen Peak, California 



This new lava, which erupted May 22, 1915. overflowed the crater rim northeast into 



the head of Lost Creek. 



found to contain a number of compact, dark inclusions, apparently early secre- 

 tions from the magma. As the soft material of the bomb, when relieved from 

 pressure by being ejected, enlarged radially by the expansion of the contained 

 gases, it elongated the vesicles in the viscous lava and drew away from the 

 solid inclusion on lines perpendicular to the bread-crusted surface, showing 

 clearly that at the time of its ejection the mass of the boulder was viscous. 



I SOURCE or HEAT JX VOLCANIC ACTIVITY 

 J'.Y LEASON H. ADAMS ' 



(Abstract) 



The object of this note is to direct attention to the thermal effect accom- 

 panying extrusion as a competent source of heat for volcanic phenomena. 



1 Introduced by II. S. Washington. 



