effects. No one now goes to the Park on account of its mineral 

 waters. It would, therefore, be premature to assume that there is 

 no medicinal virtue in them. Two great drawbacks are to be 

 encountered, and these alone are sufficient to explain why the Yel- 

 lowstone will probably never become a resort for invalids. Inacces- 

 sibility, length and severity of the winters are sufficient obstacles 

 to the National Park ever becoming such a resort. The open 

 summer season lasts only about three months. 



The hot springs and geysers, on the other hand, are interesting 

 to the geologist, because of the remarkable phenomena connected 

 with their origin and activity ; to the botanist they are fascinating, 

 because of the low forms of vegetal life found existing in them 

 even at high temperatures. 



As before stated, the waters which run from the hot springs and 

 geysers of the Yellowstone m.ay be comprehended under two heads — 

 those which deposit silica, as sinter, and those which form calcium 

 carbonate, as travertine. The last-mentioned substance is only 

 found in the Mammoth Hot Spring Basin ; the latter makes up the 

 characteristic formations of the Norris, Lower and Upper Geyser 

 Basins. The question naturally arises, how are the beautiful terraces 

 which surround many of the hot spring centres formed ? Are they 

 not simply built up by the deposition of new material from the over- 

 flow water, as it evaporates and cools at the surface ? At first sight, 

 it would seem that the craters and bowls of the geysers and hot 

 springs were foimed in this way, because we know that boiling 

 water, under pressure, will dissolve and hold in solution much more 

 inorganic material than ordinary river or spring water at the normal 

 temperature, and that in many instances, when the pressure is 

 relieved and the temperature lowered, the water will precipitate its 

 mineral contents. 



In the case of the richly carbonated waters of the Mammoth Hot 

 Springs, calcium carbonate is deposited by the relief of pressure, by 

 the escape of the carbon dioxide and by the evaporation of the 

 water ; but this physical process is not the sole cause of the varied 

 and beautiful terraces, which will presently be described. At the 

 Norris Geyser Basin, relief of pressure and cooling will cause a 

 separation of silica from the hot waters, but the waters of the other 

 geyser basins contain very much less silica, and, as far as has been 

 observed by geologists, neither relief of pressure nor cooling will 



