THE WORK OF GROUND-WATER. 



239 



Fig. 216.— Cone (or crater) of Grotto Geyser, YelloAvstone Park. (Detroit Photo. Co.) 



about themselves, the cone being of material deposited from solution. 

 In the Yellowstone Park the pre- 

 cipitation of the matter in solution 

 (chiefly silica) is partly due to cool- 

 ing and partly to the alga^ which 

 abound even in the boiUng \Aater, 

 and the brilhant colors of the depos- 

 its about the springs are attribu- 

 table to these plants. When the 

 water from any geyser or hot spring 

 ceases to floAV the plants die and the 

 colors disappear. The details of the 

 surface of the deposits about geysers 

 and hot springs are often comph- 

 cated, and frequently very beautiful 

 (Fig. 218). 



The heating of geyser and hot- 

 spring water must cool the lava or 



Fig. 217. — Cone of Giant Geyser, Yellow- 

 stone Park. (Wineman.) 



