SINTERS AT STEAMBOAT. 341 



waters, the proof that tlie water which uiulermiiied the basin south of the 

 furnaces was similar to that now issuing- near tlie railway is neg-ative. At 

 Sulpliur Bank, however, we have springs of similar (puilitative composi- 

 tion which are not depositing- sinter to any extent and which are actually 

 removing material by their solvent action. The difference at the two 

 localities appears to depend largely upon the rpiantity of sulphuric acid 

 generated. At Steamboat, also, the depressed basin contains sulphates, 

 which have been formed by the action of sulphuric acid on the rock.s, 

 and I can see no reason to doubt that the quantity of sulphuric acid 

 generated has determined deposition of sinter or removal of constituents 

 of the rocks. 



The silica of the sinters. — As has beeu Stated, one portion of the sinter area 

 consists almost solely of a flinty or chalcedonic mass. This is by no means 

 ancient, for scalding steam still issues at one point, nor does it show any signs 

 of erosion. Under the microscope the sinter is found to be composed of ordi- 

 nnry quartz crystals and fibrous, crystalline silica. No opal was detected 

 with certainty by the microscope. This rock is almost absolutely identical 

 with some of the chalcedonic specimens from Knoxville, which contain, in 

 addition, cinnabar. The sinters from the springs now most active are finer 

 grained than that just described. They are composed of silica and carbon- 

 ates. The silica is certainly in part crystalline and does not remain dark 

 between crossed nicols. 



To obtain further information about the existence of opal, water deter- 

 minations were made of three specimens, care being taken to separate the 

 water from other volatile constituents. One of the specimens was a milky- 

 white, compact rock with dull luster; a second was a very dark slate-col- 

 ored rock with a resinous luster; and the third, a pure-white sinter, earthy 

 and friable in part. The water absorbed in a calcium chloride tube was 

 in the order of the descriptions 0.72, 3.77, and 0.67 per cent. These ex- 

 periments show that hydrous silica was present in three specimens and 

 that they were true chalcedonies, if by that term is understood a mixture 

 of crystalline and amorphous silica.^ It is evident from these observations 



' Some remarks wiU be made io Chapter XIV on auotUer use of the word olialcedony. 



