164 The America)) Geohxjist. September, 1897 
hot springs, paint pots, and mud i)utfs — all different stages of 
the same phenomena — represent the mighty conflict of mete- 
oric waters and volcanic fires. As Bunsen explained, water 
collecting in a tube, which is very deep and very liot at the 
bottom, is heated far above the boiling point, since it is under 
pressure. Circulation setting in, liot portions of the water 
reach a point at which the expansive force of the steam ex- 
ceeds the confining power of the pressure and fiash into steam. 
One explosion creates a vacuum ; the vacuum, relief of pressure 
at greater depths. This in turn allows another explosion and 
so on until equilibrium is restored. If the tube is shallow or 
heat applied at the sides or the heat is not very great instead 
of a geyser there occurs a boiling spring. Less heat would 
produce a hot pot ; less water a mud pot. If the mud is 
colored it is called a paint pot. 
The springs differ not only in size, shape, temperature, and 
amount of water but also in the miture of the substances dis- 
solved in them. Ordinary water has the power of dissolving 
a large number of mineral substances. The number is enlarged 
and the power of the action is increased if the water is in- 
tensely heated. The presence of various gases and chemicals 
in the water gives another great increase in its power of de- 
composition. In the park the water is abundant, highly heated 
and full of powerful corrosives. The deposition of dissolved 
materials around the mouth of the springs is enormous. 
There are three principal kinds of springs, acid, calcareous, 
and alkaline-siliceous. The acid springs (which are the least im- 
portant) deposit alum, sulphur, soluble salts of iron, and some 
of them contain hydrochloric acid (Norris Basin). They do 
not affect the scenery materially. 
Far more important are the calcareous springs like those of 
the Mammoth Hot Springs basin. They contain chiefly cal- 
cium carbonate, and also calcium sulphate, magnesium sul- 
phate, calcium chloride, alumina and silica. The deposits cover 
three square miles with several hundred feet of travertine. 
The soui'ce of this lime is interesting. It is doubtless derived 
from the Cretaceous limestones which underlie the rhj^olite, 
filling up the basin. 
The most interesting and important of all the springs are 
the alkaline-siliceous for geysers occur only with them. They 
