THE METAMORPHIC ROCKS OF ADELIE LAND. STILLWELL. 187 



The presence of definite shear planes has been noted in two examples from this 

 locality. The shear plane may look like a thin vein in the hand specimen, and under 

 the microscope is marked by decrystallisation. The hornblende and biotite may become 

 very pale and even decolourised. The presence of finely granular talc is indicated, 

 and pyrite is distributed linearly along the shear plane. 



At Garnet Island two types of amphibolite have been described. One type is noted 

 for the abundant circular areas of pyroxene diablastically set in felspar. The pyroxene 

 is sometimes altered to hornblende and sometimes to a fibrous product. Scapolite 

 is frequently discovered in these areas. Rarely these areas are replaced by ragged 

 garnets ; but no definite evidence can be gathered to show that the garnets break up 

 into pyroxene and felspar. 



The second type of amphibolite at Garnet Point carries a small garnet percentage 

 evenly distributed through the rock. Again the garnet is always set in a felspar base, 

 and a relation to the garnet amphibolite of Still well Island is indicated. Features, 

 similar to those in the shear zones in the Cape Pigeon Rocks, are also found, but no 

 definite linear direction is obvious in them. Decolourised hornblende and talc are 

 prominent in these areas, and the colourless hornblende may be fringed with blue 

 glaucophane. Sometimes the crystals of colourless hornblende are bent and broken 

 and linear pyrite may be found. Scapolite is here associated with these areas. 



The various types may be summarised thus 



No. 



Cape Gray 773 Plagioclase Pyroxene Gneiss. 



766 Hornblende Plagioclase Pyroxene Gneiss. 



Stillwell Island 951 Plagioclase Pyroxene Gneiss. 



942 Hornblende Plagioclase Pyroxene Gneiss. 



935 Garnet Plagioclase Pyroxene Gneiss. 



953 Garnet Amphibolite. 



952 Amphibolite. 



Cape Pigeon Rocks .... 767 Hornblende Plagioclase Pyroxene Gneiss. 



782 Augite Amphibolite. 



771 Amphibolite. 



786 Augite Amphibolite (without dyke form). 



Garnet Point 781 Amphibolite. 



799 Garnet Amphibolite. 



Four chemical analyses of this rock series are given. These show a strong family 

 likeness and possess the general characters of basic igneous rocks. The Osann group 

 values place them quantitatively in the group of eclogites and amphibolites. The 

 plagioclase pyroxene gneisses are placed in the kata division of this group and the 

 amphibolites belong to the meso division. The hornblende plagioclase pyroxene gneisses 

 are transition members between the two divisions. 



