372 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



like cone surmoimtiiig a broader roound of deposit. In Iceland these 

 chimneys appear to be absent, nor are they so prominent in Kew Zea- 

 land, the latter region appearing to be intermediate in this respect. 

 Most of its geysers are described as pools of considerable size. 



Prof Joseph Le Conte, in his "Elements of Geology,-' page 104, says: 

 "The more chimney-like form of the craters in the case of the Yellow- 

 stone geysers is probably due to the greater abundance of silica in solu- 

 tion." This is not the case, as a single glance at the table in chapter YII 

 will show that the proportion of silica is usually less in the Yellowstone 

 Region than in either of the others. The one exception opal spring has 

 no cone or chimney. This fact also points in the direction of greater 

 age for the Yellowstone geysers. I think the reason for the greater 

 prevalence of the chimney-like form in the Yellowstone Eegion is satis- 

 factorily explained on the ground of their greater age. We have no 

 data for a comparison of the actual thickness of the sediments or depo- 

 sitions of the three regions, and if we had they might be to a certain 

 extent misleading, as the rate of deposition must be variable. A great 

 antiquity can certainly be accorded all three of the regions. 



Section II.— PHYSICAL AND THERMAL CONDITIONS. 

 CHAPTER V. 



FORMS OF BASINS, OENAIMENTATION, AND COLOR OF THE WATER. 

 FORMS OF BASINS AND OENABIENTATION. 



No matter where we find thermal springs we find that certain condi- 

 tions are the same. Wherever calcareous springs are seen, the deposits 

 assume certain forms, one of the most constant being that of the beauti- 

 ful bath-like basins (Fig. 18) arranged in terraces so characteristic of the 

 Mammoth Hot Springs of Gardiner's River. The same forms are seen at 

 Hierapolis, in Asia Minor, and in fact wherever springs exist that con- 

 tain a large percentage of calcium carbonate. It is not necessary that the 

 water should be hot. In the cavern of Luray, in West Virginia, basins 

 similar to those mentioned above are found. The same form of basin is 

 also seen in siliceous springs, but they are not so marked, as the depo- 

 sition of the siliceous sediments is not so rapid. The Te Tarata, in New 

 Zealand, is the most marked instance of siliceous terraces. Many of 

 the springs in the geyser basins of Fire Hole River show these terraces 

 on a small scale. They are well marked on the slopes leading from the 

 Old Faithful Geyser. This form of basin is characteristic of slopes over 

 which the water flows from the main springs. The shapes and forms of 

 the latter present an almost inconceivable variety in the various Geyser 

 Basins of the Yellowstone Park. Perfect funnel shapes are seen, as in 

 the Black Sand Geyser in the Upper Fire Hole Basin (see Plate XXYIII 

 in Part I). Others are bowl shaped, while still others are in the form 

 of basins surmounting tubes. The j)lates in Part I will give the reader 

 a clearer idea of the external forms and ornamentation of the springs 

 than can be given in words. Some of these deep pools are beautiful 

 beyond description. Filled with brilliantly clear water of sea-green 

 turquoise and indigo-blue tints, the pure white siliceous basins are in- 

 describably lovely. The corrugated sides of some break the light into 

 its primary /sonstituents and reflect veritable rainbows. Some of the 



