THE METAMORPHIC ROCKS OF ADELIE LAND 8TILLWELL. 121 



to find parts which have been unaffected by the migration. Hence Bastin's criteria 

 will apply to parts of an area, but which part ? This question will be more readily 

 answered if it should subsequently be found that metamorphic diffusion and 

 metamorphic differentiation products are restricted to a certain few rock types. 



7. CONCLUSION. 



Our reference to other areas of metamorphic rocks may now be concluded by 

 tabulating the different hypotheses appearing in the geological literature, which are 

 founded on the transition between two rock types in metamorphic areas. 



1. Intermingling of basic magma with acid magma. 



2. Differentiation of an intermediate magma into a relatively basic portion 



and a relatively acid portion. 



3. Local melting or refusion in situ. 



4. Gradual assimilation of pre-existing basic sediments by invading granite or 



gneiss, producing amphibolite as the final product. 



5. Production of amphibolite by the extreme metamorphism of a limestone. 



In each case, except the last, the observed transition takes place, as at Cape Denison, 

 between a granitic gneiss and a basic rock related to amphibolite. In all cases, 

 as far as can be judged at present, the evidence submitted might be explained on the 

 hypothesis of metamorphic diffusion. 



