102 



IGXEOUS AGENCIES. 



diameter, on the top of a mound thirty feet high. From the bottom of 

 the basin descends a funnel-shaped pipe eight or ten feet in diameter, 

 and seventy- eight feet deep. Both the basin and the tube are lined 

 with silica, evidently deposited from the water. The natural inference 



is, that the mound is built up by deposit from the water, in somewhat 

 the same manner as a volcanic cone is built up by its own ejections. 

 In the intervals between the eruptions the basin is filled to the brim 



