THE METAMORPHIC ROCKS OF ADELIE LAND STILLWELL. 



185 



pressure without alteration in temperature may produce garnet, while a decrease of 

 temperature without alteration in pressure may produce hornblende. The hornblende- 

 forming conditions may follow the garnet-forming conditions. We think this is 

 indicated by rocks like No. 942, which is similar to the garnet amphibolite in structure, 

 but the garnet is replaced by pyroxene felspar areas. If, then, we place the garnet 

 amphibolites among the meso zone rocks, it must be borne in mind that the same meso 

 conditions do not produce both garnet and hornblende. The garnet amphibolites 

 are not kata zone rocks and their family characteristics are too definite to allow them 

 to be considered as transition types between the kata types and the meso types. 



a c 



Fig. 14. 



IV. Mean Position of Group IV., the Eclogites and Amphibolites 

 773. Plagioclase Pyroxene Gneiss, Cape Gray. 

 799. Garnet Amphibolite, Garnet Point. 



767. Hornblende Plagioclase Pyroxene Gneiss, Cape Pigeon Rocks. 

 794. Plagioclase Pyroxene Gneiss, Madigan Nunatak. 

 953. Garnet Amphibolite, Stillwell Island. 



The CrystaUoblastic Order. 



The crystalloblastic order for the plagioclase pyroxene gneisses appears to be 

 Pyroxene, hornblende ; biotite ; ilmenite ; felspar. If garnet appears, as in No. 935, 

 garnet is placed above the hornblende. 



In the garnet amphibolite the order is Garnet, hornblende, biotite, ilmenite, 

 felspar, quartz. 



