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every one that is diminishing in splendor or becoming extinct a new 

 m one is preparing to take its place. The gradual manner in which all 

 these changes take place, and the enormous amount of geyserite accum- 

 lated around the craters of different geysers give some idea of th< 

 countless ages that must constitute the life period of each. Old Faith- 

 ful Geyser,. for example, appears to have built np no less than live cones, 

 the remains of which are to be seen grouped about it in different stages 

 of disintegration, the most recent of which is still 15 feet in height, 

 while its present mound is 12 feet above the surrounding surface, and 

 measures 145 by 215 feet at the base, all formed by deposit from the 

 water, and yet the amount accumulated in a single year is but the mere- 

 est film. It is probable, therefore, that whatever may eventually be 

 the fate of these rare and wonderful objects of interest, the time is st ill 

 remote when they will have become extinct or even materially dimin- 

 ished in splendor. 



The now generally accepted theory of geyser action was first an- 

 nounced by Professor Bunsen, after a careful study of the Iceland gey 

 sers, and it may be interesting in this connection to refer briefly to the 

 principles upon which it is based, in order to see whether they fulfill all 



the conditions presented by the geysershere in the Yellowstone Basin. 



It will be remembered that, while water boils at a temperature of 212 

 Fahrenheit, under the ordinary weight of one atmosphere, a greatei 

 degree of heat is required to form steam when the water is subjected to 

 pressure, as, for example, at the bottom of a long vertical tube, where 

 the whole column from above presses upon the water below. The amount 

 of h<eat required to form steam at the bottom of such a tube would be 

 greater than at the top, and the difference would be in proportion to the 

 pressure exerted by the superincumbent column. Now, when water ra 

 heated under pressure in this way it has the property of expanding into 

 steam when the pressure is removed, and if it be strongly heated under 

 heavy pressure, as at the bottom of a geyser tube, and the pressure be 

 suddenly and largely relieved as by throwing out a considerable por- 

 tion of the water, a large amount of steam will form with sudden and ex- 

 plosive violence. This, it is thought by Bunsen, is the vis a tergo at the 

 bottom of all eruptive geysers. And now for the mechanism by which, 

 in the laboratory of nature, these few simple principles are applied to 

 bring about the wonderful results which we have seen. 



The geyser must have a tube of reasonable length and width, extend- 

 ing more or less vertically into the earth ; a supply of water from the 

 surrounding surface, as wells are supplied, for example, heat sufficient 

 in amount and applied to the tube at a reasonable depth below the sur- 

 face. The variation of these conditions and the modifications of them, 

 which will be explained farther on, is all that is necessary to give variety 

 to the character of the geyser, and when they are exceeded its activity 

 fails. 



The heat— One of the first things that arrests our attention in entering 

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