230 THE ERUPTION OF VESUVIUS IN APEIL, 1906. 



lava was sufficiently cool after a few days to allow access to the 

 houses, the chambers not filled with it had a suffocating temperature. 



The weak conductivity of the lava for heat explains why all com- 

 bustible objects were not immediately consumed, but the carboniza- 

 tion of the woodwork proceeded slowly, contributing to the vapors 

 emanating from the magma itself. The chimneys and the conduits 

 of the gutters gave forth much smoke or currents of heated air. To 

 this weak conductivity is due further the survival of trees hardly 

 carbonized at the base, protected by a crust of lava that congealed 

 rapidly at their contact. Investigations may reveal interesting min- 

 eralogical alterations in the houses that have been overwhelmed. In 

 other instances devitrification of glass and crystallization of silver, 

 zinc, and copper and the formation of new minerals have been 

 observed, and such alterations will have a special interest in this 

 instance from the leucitic nature of the lava. 



All the particulars of the progress of the lava present a striking 

 analogy to those of the thick flows of mud. This is easily explained 

 by the fact that in both cases they are the result of fluidit}^ of the 

 mass in motion, due in the one case to temperature and in the other 

 to the presence of water. 



EXPLOSIVE PHENOMENA. 



STKOMBOLIAN EXPLOSIONS. 



These present no special point of interest except their intensity 

 during the night of April 7, in the course of which the emptying of 

 the crater by the great flow brought them to an end. They furnished 

 bombs and vitreous scoriae, a part of which was very light. The 

 form and structure of the material attest the great fluidity of the 

 magma at the time of ejection. On my arrival these deposits were 

 completely covered b}^ the material of the Vulcanian explosions. 



VULCANIAN EXPLOSIONS. 



These in all respects form the chief interest of the eruption. Their 

 characteristic traits have already been described. The enormous 

 columns of clouds developed to a height of several thousand meters 

 above the crater. Dense, gray or black in color, seamed by lightning, 

 accompanied by heavy detonations, they were successfully thrust 

 forth, the one into the other, like puffs from each stroke of a steam 

 engine under strong pressure; later the ascension was less rapid; 

 the columns rose majestically upward, merging into one another; 

 still later they mounted slowly, then for some minutes remained 

 stationary above the crater till dispersed by the wind. Avalanches 

 of solid material descended from their base, but in no case did they 

 become sufficiently dense to assume the Peleean form. Often in the 



