CG PROCEEDINGS OF THE AMERICAN ACADEMY. 



problem. The thermal energy is clearly derived from magma. The 

 small amount of water ejected in the average geyser eruption, when 

 compared with the observed diameter of the geyser's throat below its 

 funnel, shows that the level of superheating is, on the average, not 

 more than a few hundred meters below the surface. The heat can 

 hardly be regarded as that residual from a Pliocene lava-flow even 

 600 meters thick. The specific heat of water is from three to five 

 times greater than that of rock-matter between the temperatures of 

 100°C. and 1000°C. 



Allowing for radiation above and conduction below the lava flow ; 

 considering also that the rhyolite was erupted tens of thousands of 

 years ago, that the rhyolite is comparatively permeable for the chilling 

 rain-water, and that the visible abstraction of heat from the rhyolite 

 by the springs is continuous and rapid, — one must doubt the hypothe- 

 sis that the original heat of even such a thick flow can be responsible 

 for the present activity of the geysers. The hypothesis suffers, too, 

 from the difiiculty that it does not explain the high temperatures of 

 the Mammoth Springs. These emerge from a Mesozoic terrane which 

 lost its rhyolite cover (a sheet formed by lateral outflow from the main 

 area of extrusion) in pre-Glacial times. The same point may be urged 

 in the case of other hot springs, such as those in the bottom of the 

 Grand Canyon of the Yellowstone. At each of these localities the heat 

 is passing upwards through the relatively thin roof, composed of the 

 country-rock of the batholith. 



It would, therefore, seem just to refer the geyser temperatures to 

 one or more great subterranean masses (batholiths) extending, nearly 

 or quite continuously, 120 kilometers from north to south and 30 to 50 

 kilometers from east to west. Heat will pass upward from such a 

 batholith either by simple conduction through the roof-rock or by 

 gaseous transfer. The analyses of the spring-waters suggest that some 

 magmatic gas has been added to the ascending meteoric water, which 

 may have attained its high temperature to a certain extent from the 

 hot gas.28 But this cause seems quantitatively insufficient to keep 

 the geysers working at their observed speed, and simple conduction 

 through the rock is more likely to be the essential cause. 



In whichever way the heat is applied to the water, it seems clear 

 that the actual batholith must be at or near the surface in each geyser 

 area. The shallowness of the zone of superheating shows a very steep 



2' The peculiarly intense alteration of the rhyolite is, in part, explicable 

 on the assumption that the magmatic gases (specially abundant in the upper 

 part of every batholith) have slowly passed out through the rhyolite shell 

 after that shell had solidified. 



