IGNEOUS AGENCIES. 



137 



erupted are 1. Rock-fragments. 2. Lava. 3. Cinders. 

 4. Sand. 5. Ashes. 6. Smoke. 7. Gas. The rock-frag- 

 ments are formed in explosive eruptions by the breaking 

 up of the hardened floor of the crater, and require no 

 further explanation. 



Lava. This term is applied to melted rock, or to the 

 same after it has hardened again. The degree of liquid- 

 ity depends partly on the degree of heat and partly on the 

 kind of fusion. The lava of Kilauea is as liquid as honey. 

 The bursting of bubbles on the surface of this thin, VIS- 



FIG. 70. Lava-tunnel, and "spatter-cone" formed by escaping steam, Kiluueu. 

 (Photograph by Libbey.) 



cous liquid draws it out into hair-like threads like spun- 

 glass, which is borne by the winds and accumulated in 

 certain parts of the crater. This is called " Pele's hair." 

 Thin hivji like this, when it first issues from the crater, 

 runs with ^rca-l velocity, twenty to twenty-five miles an 

 hour ; but as it cools it becomes stiffer, first like tar, then 



