WEST INDIAN VOLCANIC ERUPTIONS 



209 



evidently outlets of underlying heated deposits, which, whenever 

 reached by sufficient water, expressed themselves by the geyser- 

 like eruptions. 



Process of eruption. — Over the bed-rock bottoms of the periph- 

 eral streams a certain considerable amount of flood-plain deposit 



Fig. 6. — Mud flows on Blanche Lake divide. 



had taken place before the eruptions. Upon this plain, and well 

 up upon the including valley walls, were deposited hot volcanic 

 ejecta of dust and bowlders. The high temperatures of the 

 latter were maintained, aided by the blanket covering of over- 

 lying ash; and by their gravity they had tended to gather in the 

 old river channel, forming loci of concentrated temperatures. 

 Into these heated beds water percolated from above. The vapor 

 generated by contact with the hot rocks increased until it sud- 



