ORIGIN OF FOLDED MOUNTAINS — PROUTY 303 



originally molten, on the cast side of the continents, and, through this 

 action they should be building out a thinner crust toward the east. 



Since the acid rocks of the continents contain about twice as much 

 radioactive material as the basic rocks of the subcrust, the thicker 

 continents should reach, in their basal portion, a condition of fusion 

 before the basic rocks of the subcrust. This would bring about an 

 elevation of the continent, followed by injection and ultimate spread- 

 ing of the continent, with folding of the continental borders; all 

 entirely independent of the general basaltic fusion. This source of 

 folding has been emphasized by both G. R. MacCarthy and W. F. 

 Prouty in recent articles. 



ASTHENOLITHS 



Bailey "Willis in his recent articles on Continental Genesis and 

 Metamorphic Orogeny, has laid stress on the importance of crystal 

 growth in the metamorphic rocks as a source of lateral compression 

 in mountain building. According to his theory, tidal and rotational 

 forces have developed diagonally orientated strain zones in the earth 

 outside the inelastic core. These strain zones in the deeper earth are 

 favorable to rock fusion. The magma thus formed tends slowly to 

 melt its way toward the surface along the zone of strain and to pond, 

 along with other magma locally formed, beneath the poorly heat- 

 conducting, crystalline outer crust. These local pockets of molten 

 rock may reach dimensions of several hundred miles. The cumula- 

 tive shearing stresses, associated with the growth of such an astheno- 

 lith, ultimately cause eruption around its border. This is followed, 

 finally, by a central collapse. According to Bailey Willis, some of 

 the extinct asthenoliths are marked by the larger depressions in the 

 ocean basins, while the present active forms are marked by certain 

 deeps " characterized by great seismic activity and beside wdiich rise 

 great mountain chains of volcanic or intrusive formations." During 

 the life of this molten pocket, metamorphism of the surrounding 

 rock is taking place with the formation of a flock of new minerals. 

 The growth of these new minerals is largely in the horizontal plane, 

 the direction of least resistance, and as the crystal growth exerts a 

 pressure as great as the crushing strength of the crystal, and, there- 

 fore, the rock, we have here a tremendous lateral force in the areas 

 of metamorphism. Such asthenoliths tend to form under both ocean 

 and continent, but those which form under the continents have a 

 stronger tendency to approach the surface along the continental 

 borders than elsewhere. 



The above theory of asthenoliths would explain both the igneous 

 activity and the formation of the arcuate folds in tiic coastal island 

 mountains of Asia. While the assumptions of the theory do not 

 seem to be necessary to account for local pockets of molten rock 



