120 H. S. JEVONS, H. I. JENSEN AND C. A. SUSSMILCH. 



was caught by consolidation at a certain transient stage 

 that any identifiable record would remain. If crystallis- 

 ation occurred soon after emulsification, each globule would 

 probably form one crystal, or only part of one, and the 

 resulting rock would not differ from one crystallised from 

 a homogeneous magma. On the other hand, if the magma 

 had been sufficiently hot and fluid for nearly complete 

 separation of the heavier liquid, we should find a mass 

 probably richer in femic minerals in its lower part, passing 

 more or less gradually into a more acid rock into the upper 

 part, a phenomenon which might have been caused by other 

 methods of differentiation. It would only be where the 

 minute drops of the emulsion had united into larger globules, 

 and where for some cause, such perhaps as the viscosity 

 of the magma, or the rapidity of cooling, these globules 

 had not sunk to form a lower layer, that we might expect 

 to find traces of them preserved. Such a case appears to 

 be the granite with spherulites crystallised from without 

 inwards described by B'ackstrom. Is it not possible that 

 if the attention of petrologists were more uniformly directed 

 to the characters of liquation phenomena, further dis- 

 coveries of them would be made ? 



Differentiation during Consolidation. 

 Differentiation may occur during the consolidation of a 

 magma in several ways, all of which, however, merely 

 amount to the separation of the earlier formed minerals 

 from those crystallising later. The simplest method is by 

 the sinking of the first formed constituents. When these 

 are femic minerals their specific gravity must be consider- 

 ably greater than that of the magma in which they form, 

 for they are denser than the average specific gravity of the 

 solid rock, and the latter is greater than the specific gravity 

 of the same rock in the liquid state. 1 



1 According to the data of JBarus, and the observations of Joly who 

 noticed considerable expansion of rock on melting. 



