116 A. HAGUE THERMAL WATERS IN YELLOWSTONE PARK 



analysis, ranges from .22 to .67 grams per kilogram of water, the former 

 being the amount found in the cauldron of the Excelsior, having the 

 largest outflow of any pool in the park, and the latter from Opal Spring 

 in Norris Basin, with but slight run-off and without any apparent inflow. 

 The cause of these differences is, I believe, to be sought in the varying 

 amounts of infiltrating surface water. 



Dr. W. H. Hallock has shown conclusively, by experimental tests with 

 self-registering thermometers, that the thermal waters stored in under- 

 ground geyser reservoirs possess a temperature far in excess of the boiling 

 point at the surface, due to increased pressure of the overlying column 

 of water in the geyser tube. The results were in accord with the theo- 

 retical boiling point. It can not be affirmed positively that these super- 

 heated waters maintain the same composition after being thrown out as 

 the underground waters at greater or less depth or even with those of 

 the geyser reservoirs. On the other hand, there exists no evidence of 

 chemical changes due to relief of pressure before the waters reach the 

 surface through geyser orifices. 



On the relief of pressure, hydrated silica, associated with traces of an 

 equally insoluble silicate of alumina and lime, is deposited on the broad 

 plains of the geyser basins. Nearly all remaining constituents are car- 

 ried away in solution by surface streams. Although the composition of 

 the deposited sediment is everywhere much the same, its external habit 

 varies with the manner of its secretion, which may have happened in 

 several ways. It may have been caused by precipitation on relief of 

 pressure, precipitation on cooling, separation by evaporation, and assimi- 

 lation by algae. Mr. Walter H. Weed has shown conclusively the im- 

 portant part such organisms perform as geological agents in the accumu- 

 lation of sinter deposits.^ 



The volume of siliceous alkaline waters far exceeds those of the acid 

 type. On the other hand, the latter occur more widely distributed, are 

 more complex in their composition, and consequently more varied in their 

 deposits. These acid waters come to the surface through fumaroles, sol- 

 fataras, and the so-called mud springs and paint pots. In nearly all 

 such occurrences the waters carry either free hydrochloric or sulphuric 

 acid. In general these thermal waters, which rise through narrow seams 

 and rifts, run but little water and leave behind only thin incrustations 

 around the sources of supply. These deposits are found widespread over 

 the park and consist principally of sulphates of alumina and double com- 

 pounds of alumina and iron. While they show a mingling of saline 



5 Wnlter H. Weed : Formation of travertine and siliceous sinter by the vegetation of 

 hot springs. U. S. Geological Sur-ey, Ninth Annual Report, Washington, 1890. 



