THE METAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 209 



of the sphene rim can be pictured, if necessary, as produced by reaction of the Ti0 2 

 content of the magnetite with the felspar. Mere differences in rates of solid diffusion 

 of the different constituents will not explain why felspar and magnetite have travelled 

 in one direction while the ferro-magnesian goes in the other. The driving force wliich 

 controls the direction of migration of the chlorite or of magnetite molecules we express 

 in the term " Force of crystallisation." Stead, in the above-mentioned study on 

 the segregatory habits of solids in alloys, recognised this driving force in the term 

 " Crystallic attraction." 



The force of crystallisation, or the power that a crystal has of drawing to itself 

 molecules of its own kind, has been demonstrated by Becker and Day* to be, in 

 supersaturated solutions, commensurate with the crushing strength of the rock. It is 

 the same force which, varying in different minerals, produces the crystalloblastic order. 

 It is, therefore, an important. factor, and can be pictured as a directive agency in the 

 recrystallisation of rocks. 



" linear Force of Growing Crystals," Becker and Day, Proc. Wash. Acad. Sci., vol. VII., 1905, pp. 283-288. 



Series A, Vol. in.. Part 1 O 



