4 



produce a separation of the silica. Water collected from the springs 

 and geysers of the Upper and Lower Geyser Basins was perfectly 

 transparent, and remained clear and without sediment after standing 

 for several years. Experiments "Showed that the silica in these 

 waters remained dissolved, even when the water was cooled down to 

 the freezing point, and it was only after the crystallization of the 

 water by freezing that the silica was separated and settled down as 

 an insoluble flocculent precipitate upon melting the ice. 



How, then, are we to account for the production of the exquisite 

 terraces, mounds, pools and geyser cones? It has been proved, in 

 addition to the causes operative in the above instance, that the rapid 

 deposition of the sinter and travertine from both classes of water is 

 due to the action of vegetation in removing the carbon dioxide from 

 carbonated waters, thus depositing calcium carbonate, and, in the 

 case of the silicious waters, depositing by the activity of the proto- 

 plasm a gelatinous silica, which, upon exposure, finally hardens. 

 We know, from numerous observations, that plants are active in 

 rock building and disintegration. 



The plants of the Carboniferous Period, by their death and con- 

 solidation, formed the extensive and useful coal beds. Sphagnum 

 and mosses compacted yield peat, and, in some cases, soft coal. Sili- 

 cious diatoms have given rise to extensive diatomaceous earths. 

 In several of the higher algae, for example, Halimeda opjintice, the 

 carbonate of lime deposited by the plant forms a sieve-like cover 

 about the tips of the algal filaments, and, in Acetabularia, it occurs 

 as a tube about the stalk of the plant. In the chak.e the lime is 

 separated and deposited in the cells and cell walls of the back alone, 

 while in the Corallines it is found only within the cells. Nor is our 

 knowledge of the activity of protoplasm in the deposit of mineral 

 substance solely confined to plants. We know that many animals 

 secrete silex and carbonate of lime, foraminifera, coral polyps and 

 molluscs generally. Before, however, we can understand the part 

 which vegetation has played in forming the travertine and sinter 

 beds of the Yellowstone Park, we must become familiar with the 

 general appearance and character of the deposits themselves. 



First in importance among the many points of interest accessible 

 are the Hot Spring Terraces. These have been built one upon 

 another, until the present active portion constitutes a hill rising 300 

 feet above the site of the Mammoth Hot Springs Hotel. The for- 



