306 



DYNAMICAL GEOLOGY. 



north of Yellowstone Lake, and six from " Crater Hills." Some of the mud 

 pools are simply muddy water; others are like kettles of boiling soap; some 

 like caldrons of mush or paint, and still others like 3tif£ mortar. They vary 

 in stiffness with the dryness of the season. They have generally a circular 

 pit 10 feet deep, and rise sometimes into a mound several feet above the 

 general level. All together, the number of hot springs and geysers in this 

 region cannot be less than 10,000. The hot waters are usually siliceous, 



279. 



and deposit the silica in the form of a tufaceous or porous opal called gey- 

 serite. It makes cones and basins of various shapes, and covers the surface 

 over wide areas. The deposits of the Gardiners River at the Mammoth Hot 

 Springs are calcareous ; Fig. 282 represents one of its calcareous cones, the 



