250 H. L. FAIRCHILD — 'GEOLOGY UtfDER FLANETESIMAL HYPOTHESIS 



terior, it is difficult to see why an outflow of molten rock once begun 

 should ever cease. But the new hypothesis is more favorable to limited 

 liquidity, since it favors heterogeneity of the earth's mass and consequent 

 local variation in temperature and melting point. 



The varied phenomena commonly known under the term " volcanism " 

 are much better explained by the new hypothesis. It is evident that 

 the explosive action in volcanoes is due to the expansive power of heated 

 vapors, chiefly water. Under the old view the supply of water is from 

 the hydrosphere, but the assumption that volcanic water is atmospheric 

 is founded mainly in analogy and has little basis in observation or sound 

 reason. We may admit that the water of thermal springs and geysers 

 and perhaps of some fumaroles is meteoric, but the volcanic water is too 

 large in quantity and apparently from too great depths to be derived 

 from superficial sources. The amount of volcanic water is enormous. 

 Fouque determined that the amount of steam expelled from one of the 

 numerous parasitic cones of iEtna was equal in 100 days to 462 million 

 gallons of water. This equals 16 gallons for every square foot of a square 

 mile, or a depth of 32 inches over that area. But the steam product of 

 the single cone was probably not the one-thousandth part, perhaps not 

 the one-ten -thousandth part, of the whole product of the volcano during 

 that time. 



The interstitial water of the rocks can not be sufficient to produce the 

 vast accumulations localized in the volcanic reservoirs, and efficient cir- 

 culation at great depths seems impossible. The capacity of molten 

 magmas to absorb vapors has been used as an argument for the meteoric 

 source of the water; but an objection is that before the water can reach 

 the absorbing magma it must pass through a great thickness of moder- 

 ately heated strata, where the repulsive force is great and the absorbing 

 power is small or entirely wanting. The idea of supply through fissures, 

 subterranean or oceanic conduits, in the face of the vastly superior and 

 opposing hydrostatic pressure of the molten rock, is not worthy of 

 consideration. 



The presence of water and other gases in the crystalline and deep- 

 seated rocks is a familiar fact to the petrographer, and the theory that 

 the volcanic waters were indigenous to the earth's magma has in later 

 years been held by several students of volcanism; for example, Scrope, 

 Fisher, Reyer, Tschermak, and Stiibel. Nearly ten years ago the view 

 was emphasized before this Society by Doctor Lane,* but the repressive 

 effect of the old hypothesis has prevented the full recognition of the 

 truth and of its value. However, it has not been shown how, under the 



*A. C. Lane : " Geologic activity of the earth's originally absorbed gases." Bull. Geol. Soc. Am., 

 vol. 5, pp. 259-280. 



