270 A. C. LANE — GEOLOGIC ACTIVITY OF THE EAKTH's GASES. 



ei'UiDtion, after the first rush of gas the volcano must be fed by a viscous 

 flow of the soUd or Hquid walls and the eruption must be more quiet 

 and attended with more lava. The rock might be liquefied* in one 

 of several ways. Relief of pressure might liquefy it ; hotter gases from 

 below might assist; chemical combinations, oxidation, etcetera, may- 

 raise or hinder the fall of the temperature, and, finally, viscous motion 

 itself, like friction, tends to raise the temperature and increase liquidity. 

 On the other hand, the escape and expansion of the gas would tend to 

 lower the temperature. 



Igneous Phenomena and Causes. 



Increasing Heat and Basicity toward EartK's Center. — That the earth's 

 heat increases inward will be readily accepted, in view of the fact that 

 everywhere when boring into it we find the temperature rises ;t that 

 all material from within is hot ; and, according to astronomic data, it is 

 a globe cooling from a not incalculable past.J 



That it passes gradually from a silicious rind to a core of iron may not 

 be so easily granted, yet there is much to be said favoring it, and I know 

 of nothing against it. Such would be the natural arrangement in a cool- 

 ing globe composed of such elements. The specific weight of the earth 

 is greater than that of the rocks at the surface, as it should be, and about 

 in the right proportion.§ Absorbed gases, however, might reduce the 

 specific weight of the center. Fragments of meteorites from space are 

 often largely iron, and also often show a strong resemblance to the more 

 basic rocks of the globe. The relation of the meteoric irons to the most 

 basic earthy rocks is also indicated by many other things, as, for example, 

 the troilite of one and pyrrhotite of the other, and the association of 

 nickel. 1 1 Small masses of pure iron have been found in basic terrestrial 

 rocks. Iron is one of the abundant and widely diffused elements of the 

 earth's crust, and the quantity of it in the igneous rocks increases as the 

 amount of silica decreases. 



The fact that in a generalway rocks can be arranged in a series from 

 acid to basic is well known and has been given a definite expression by 

 Durocher and for the Iceland rocks by Bunsen. If, then, we could prove 

 that the basic lavas are from a deeper source than the acid, the induction 

 would be very strong. That this is the case is indicated by their greater 

 weight and heat. I cannot find it anywhere stated on direct observa- 



*Some so-called volcanic bombs may be uriliquefied fragments. 



t Geikie : Op. eit., p. 49 ; Neues Jahrbuch, vol. 2, 1890, p. 2M, and vol. 2, 1892, p. 39. 



JGeikie : Op. cit., p. 58; Walcott: Am. Jour. Geology, no. 7, 1893, p. G39. 



g Geikie: Op. cit., p. 48; de Lapparent : Comptes RenduS, February 19, 1889, p. 369. 



II Kosman ; NevTes Jahrbuch, vol. i, 1892, p. 83. 



