PEALE.] DEFINITION OF GEYSER. 417 



The difference between geysers and ordinary hot springs is not readily 

 explained, nor even always recognized. The difference between a quiet 

 thermal spring and a geyser in aciive eruption is very marked, but be- 

 tween the two there is every grade of action. Some geysers at times 

 api)ear as quiet springs, as for instance the Grand Geyser during its 

 period of quiescence. Others might easily be mistaken for constantly 

 boiling springs, as in the case of the Giant Geyser, in which the water is 

 constantly in active ebullition. This is true also of the Strockr of Ice- 

 land. Many of the springs, therefore, that in the Yellowstone Park have 

 been classed as constantly boiling springs may be unsuspected geysers. 

 The Excelsior Geyser was not discovered to be a geyser until eight years 

 after the setting aside of the Park. Almost all constantly boiling- 

 springs have periods of increased activity, and those which spurt a few 

 feet into the air have been classed as pseudo-geysers. 



It has been noticed that geysers occur where the intensity of volcanic 

 action is decreasing. In the neighborhood of active volcanoes, such as 

 Vesuvius, the temjierature apijears to be too high, and the vapor escapes 

 as steam from what are called stufas.* When the rocks at the surface 

 are more cooled the water comes forth in a liquid form. 



We will now pass to the consideration of the various geyser theories 

 that have been proposed by different writers. 



GEYSER THEORIES. 



HerseheWs tlieory. — The first theory I shall give here is one suggested 

 by Sir J. Herschell.t 



An imitation of geyser jets may be produced on a small scale by heat- 

 ing red hot the stem of a tobacco pipe, filling the bowl with water, and 

 so inclining the pipe as to let the water run through the stem. Its 

 escape, instead of taking place in a continued stream, is then performed 

 by a succession of violent explosions, at first of steam alone, and as the 

 pipe cools, almost wholly of water. At every such paroxysmal escape 

 of the water a portion is driven back, accompanied with steam, into 

 the bowl. The intervals between the explosions depend on the heat, 

 length, and inclination of the pipe; their continuance on its thickness 

 and conducting power. The application of this experiment to the gey- 

 sers requires that water percolating through fissures and crevices in the 

 earth should reach a fissure in which the rock is red hot. Steam would 

 then form and force its way to the surface, carrying with it some of the 

 water, and also drawing some of it back towards the source. After the 

 steam was all condensed the water would return, and a repetition of the 

 l)henomena would take place. 



McKenzie's theory. — Sir George McKenzie visited the Iceland geysers 

 in 1810, and in 1811 he proposed the following as the explanation of their 

 intermittent action: 



He supposed that the geyser tube P M (Fig. 28) communicated with 

 a cavity (A), to w^hich meteoric water had access from the surface by 

 means of fissures. The walls of this cavern are hot from the nearness of 

 the seat of volcanic fire, and also receive heat from steam that comes 

 into it by fissures at the bottom. Tliis steam, having an extremely high 

 temperature, heats the water in A to and above the boiling point. The 

 water stands at the level B 0, and the space above it is filled with steam 



*The steam from stufas usually Las temperatures far above the hoiliug point of 

 water. 



tMSS. read to Geol. Soc. of London February 29, 1H32, cited by Lyell in rriuciplea 

 of Geology, p. 555. 



27 H, PT II 



