IGNEOUS AGENCIES. 151 



column twenty feet in diameter to the height of sixty feet, 

 and through this great mass it shoots up several lesser jets 





PIG. 80. Pink terraces, New Zealand. (After Peale.) 



to the height of 250 feet. It erupts about once in eleven 

 hours, and plays twenty minutes. 



4. The Beehive, so called from the shape of its mound, 

 shoots up a splendid column two to three feet in diameter 

 to the height of 219 feet, and plays fifteen minutes (Fig. 

 82). 



5. Old Faithful, so called from the frequency and regu- 

 larity of its eruptions, throws up a column six feet in 

 diameter to the height of 100 to 150 feet, and plays fifteen 

 minutes (Fig. 83). 



Cause of Geyser Eruption.* This may be explained, 

 in a very general way, as follows : Experiments show that 

 the heat of the water rapidly increases as we pass down the 

 geyser-throat. There is no doubt, therefore, that in spite 

 of the increasing pressure (which raises the boiling-point) 



* For a complete discussion of this interesting subject, see author's 

 " Elements," pp. 99-104. 



