METHOD OF ATTAIXIXG HORIZONTAL MOTION 373 



into the country rock. While these granites were in the fluid stage the 

 expansive power of this included water and other vapors which are known 

 to be associated with batholiths must have been enormous. A definite 

 vapor pressure of atmospheres becomes, when applied to the walls of 

 batholiths hundreds of miles long, a truly enormous force, fully capable 

 of rending the rocks of the crust, just as it visibly rends those rocks where 

 volcanoes exist. 



GROWIXG CRYSTALS 



It has been long known that growing crystals exert a tremendous 

 force; the most familiar case is that of ice, but other instances are mat- 

 ters of common knowledge. Mineral crystals which grew later than the 

 body of a rock can be seen to have distorted the rock and pushed it aside 

 as if it had no strength. Many attempts at measurement of this force 

 have been made, but only recently has the equipment and the efl'ort been 

 sufficient. It has lately been determined that growing crystals exert a 

 pressure of 1,000 to 2,000 atmospheres on their confining walls. If this 

 pressure is applied to the wall of the batholith during the cooling of the 

 magma it becomes a force of the same order as that of the vapor pressure 

 in the magmas. It follows the vapor pressure after the magma has 

 cooled so far that the vapors are condensed and crystallization is well 

 under way. The pressure of growing crystals, while very intense, causes 

 a very limited motion. In this respect it is quite unlike the vapor 

 pressure, which is capable of enormous motion. The pressure of such 

 crystals may, however, have applied the pressure to the crust which has 

 obviously been at work in the metamorphism of the rocks where moun- 

 tain-building was strongest. This combination of the pressure of crys- 

 tals, together with the pressure and heat of the batholiths, seems to 

 explain the association of metamorphism with mountain-building and 

 batholithic intrusion. 



BEARIXG Oy OTHER THEORIES 



The distribution of batholiths suggested above affords an explanation 

 of many relations which are of fundamental importance but are ex- 

 tremely puzzling. Such are the epeirogenic uplifts of large regions, the 

 uplifts of large and small domes, and the reversal of such movements. 

 These have been mentioned already as grave objections to accepting 

 isostasv as a prime and sufficient cause of mountain-buildino'. If, how- 

 ever, there may be general movements of magma at depths (and it is 

 clear that they do take place locally), the situation is quite different. 

 Magmas would find the weak parts of the crust and push tliem up into 

 domes, probably doing so again and again in response to successive im- 



