360 ELEMENTARY GEOLOGY 
The fifth cause for earthquakes is the attempt of 
lava to escape. It may succeed in rending the cone, 
and thus bring about conditions favorable for violent 
eruption. In such cases the earthquake is a part of 
the eruption, as was so well illustrated at Krakatoa 
mt hdd eT Se Ty 
Fig. 219. 
Cracking of the ground along the fault-plane, revealed during the Japanese 
earthquake of 1891. The shock was caused by this faulting. 
(p. 343). Or the attempt of the lava to reach the 
surface may be only partially effective, so that the 
dyke, sheet, or intruded mass may be thrust violently 
into a fissure broken in the earth. This would also 
cause an earthquake ; and from such a source, numerous 
shocks might spring. As the earth ruptures, and the 
