THE BEHAVIOR OF INCLUSIONS IN IGNEOUS MAGMAS 567 



rock. No support in the way of reaction rims of the appropriate 

 kind has yet been found for the limestone-syntectic hypothesis. 

 Some such support is desirable before the hypothesis can be ac- 

 cepted, even though there is reason to beheve, as pointed out above, 

 that the presence of limestone might emphasize the normal ten- 

 dency of magmas to give an alkaline differentiate. 



SUMMARY 



The question whether magmas can dissolve large quantities of 

 foreign inclusions is one that has been much debated by petrologists. 

 Some have claimed great powers for magmas in this respect and in 

 addition have assigned a dominant role in the production of differ- 

 entiation to such solution of foreign matter. Others have insisted 

 that magmas have not the necessary heat content to enable them to 

 give significant effects of this kind. A study of some simple equi- 

 librium diagrams, with the object of determining the heat effects 

 connected with solution, gives every reason for believing that the 

 effect is a large absorption of heat, usually of the order of magnitude 

 of the latent heat of melting. For simple solution, then, it is 

 unquestionable that large amounts of heat will be required. 



Those who believe in the actuality of the solution of considerable 

 amounts of foreign matter in magmas have usually realized this 

 fact and have sought a source of the heat in magmatic superheat 

 of great amount, that is, in a large excess of temperature of the 

 magma above its crystallization range. A study of the probabilities 

 of the case and of the usual effects of magmas upon inclusions leaves 

 little reason for believing that magmas can ordinarily have any 

 considerable superheat. 



Unquestionably, then, the observed effects of magmas upon 

 inclusions are usually to be referred to an action other than the direct 

 solution of inclusions in superheated magma. An application of 

 the conception of the reaction series to the solution of the problem 

 affords an explanation of the effects of magmas, even though satu- 

 rated. Certain principles governing the effects of liquid upon 

 inclusions belonging to reaction series can be developed by studying 

 the equilibrium diagrams of systems involving both continuous and 

 discontinuous reaction series. In this manner it can be decided 



