CRYSTALLIZATION-DIFFERENTIATION IN MAGMAS 423 



silicate-rich.^ Apart from the objections that have been raised 

 against immiscibility in general, principally with reference to the 

 lack of evidence of the intermediate steps of the process, a further 

 objection should be pointed out that is applicable to this particular 

 type. The contrast between the two liquids should be of this 

 nature, that the one liquid should be mainly a silicate melt with a 

 little water in dilute solution, and that the other liquid should be 

 mainly water with a little silicate in dilute solution. Now, while it 

 is well recognized that the granophyre of the association to which we 

 have reference is characterized by having a greater amount of water 

 than the gabbro, no one would go the length of claiming that the 

 granophyre magma was mainly water with a little silicate in solu- 

 tion. While having, on first thought, some degree of probability 

 the action contemplated does not appear to represent the actual 

 phenomenon. 



THE ORIGIN OF NODULES, SCHLIERS, AND RELATED PHENOMENA 



Immiscibility has been invoked as an explanation of other 

 phenomena of igneous rocks, principally the formation of mono- 

 mineralic nodules and of large rock masses of a monomineralic 

 nature. For immiscibility of this nature not even the first-thought 

 probability can be conceded. Substances freely miscible above a 

 certain temperature do not become absolutely immiscible on cooling, 

 with consequent separation of pure end components as liquids. 

 The liquids separating would of necessity be yolycomponent solu- 

 tions, possibly quite strongly contrasted, but nevertheless 

 polycomponent. The liquids must likewise be solutions capable of 

 separate existence at the temperature concerned, and in emphasis 

 of this temperature aspect of the problem it has elsewhere been 

 pointed out that pure molten olivine, for example, can hardly be 

 credited at temperatures near the crystallizing range of olivine 

 basalt. It has been suggested that the. liquid need not be pure 

 olivine but could be olivine with volatile components in solution.^ 

 The obtaining of such a liquid is, however, sensibly the same prob- 

 lem as the obtaining of molten olivine. Any liquid that separated 



'Evans, "Congres Geologique International," Compte-Rendu (XXIIe Session, 

 Canada, 1913), p. 248. 



= Daly, Jour. GeoL, XXVI (1918), 123. 



