PRESIDENT S ADDRESS. 27 



There appears to me to be much difficulty in accounting for the 

 various observed land movements if these are to be attributed to 

 denudation alone, but if to this source of disturbance be added a 

 moderate amount of shrinkage through secular cooling, all classes 

 of earth movement, folding, cfec, can be much better explained. 

 From shrink ge alone, one would expect erratic tilting nnd sink- 

 ing, but not orderly regional uplifting or subsidence, and it seems 

 probable that such movements are in the main due to denudation. 

 Land may readily enough sink through denudation in spite of the 

 attend -nt removal of pressure, because that very relief may bring 

 about the liquefaction of lava previously held solid by pressure, 

 while the accompanying disturbance opens up channels for its 

 escape. 



It has during recent years be^^n increasingly manifest that much 

 volcanic activity is caused by the penetration of ocean water 

 through earthquake fissures to the interior hot part of the earth, 

 with the consequent production of steam at very high tension. 

 Large quantities of h^'^drogen chloride are at times emitted by 

 volcanoes, nnd, it bein^ now pretty well known that existing 

 plutonic waters are practically free from chlorine, the obvious 

 source of supply of this substance is the salt of the ocean water.* 

 It has been suggested that if the crust of the earth contains 

 sufficient radium to provide the heat known to exist in the 

 interior, the moon, from its supposed mode of origin, must also 

 be equally rich in radium, and should indeed have an even greater 

 internal heat than the earth. This question has been very satis- 

 factorily dealt with from the extreme radium standpoint by the 

 Hon. Mr. Strutt.t who points out that though the period of lunar 

 volcanic activity has been generally believed to be past, much 

 doubt has been thrown on this assumption by the observat ons of 

 modern astronomers, and notabl}^ by Prof-r^ssor W. H. Pickering, 

 who is decidedly of the opinion tliat changes sufficiently great to 

 be noted occur from time to time on the moon's surface. That 



See references, Proc. Linn. Soc. N. 8. Wales, 1905, p. 621, 

 t Proc. Roy. Soc. London, A Ixxvii. 472. 



