THE METAMORPHIC ROCKS OF ADBL1E LAND. 8TILLWELL. 181 



Garnet Point. 



Among the specimens of altered dyke rock from this locality two varieties have been 

 collected. The extraordinary features along the junction with the cyanite biotite 

 gneiss of one type of amphibolite (No. 769 or 781) have already been mentioned. In 

 this case a mineral which has been referred to as cyanite appears in the cyanite biotite 

 gneiss, and can be traced across the junction to a distance of at least lin. away from it. 

 At this distance it is less abundant than in the cyanite biotite gneiss. It is found in all 

 the specimens of amphibolites from this locality. 



In this amphibolite hornblende is the most important constituent ; but of nearly 

 equal importance are the circular areas of diablastic felspar and pyroxene (Plate VII., 

 fig. 4). These areas are similar in outline to some of the felspar-pyroxene areas in No. 

 942, or to the felspar-garnet areas in No. 953 from Stillwell Island. This rock, like 

 No. 953, also possesses a noticeable amount of quartz ; but nowhere do we find the 

 pyroxene fragments set in quartz. Occasionally the fibres of pyroxene are set radially 

 in the felspar. The pyroxene in the aggregates may be altered to hornblende or to a 

 cloudy fibrous mineral. Very often, when it can be determined, the pyroxene has straight 

 extinction. The aggregates may be dotted with ilmenites and small biotites, while 

 in polarised light they nearly always show a little scapolite, arising out of a fibrous mass. 

 Sometimes a mineral with high refractive index and low bluish polarisation colours 

 can be detected and suggests a zoisite. The felspar in the aggregates may be clear 

 and possess very fine, irregular, twin lamellae. The low refractive index, high polarisa- 

 tion colours, and straight extinction of the scapolite can always be observed, but its 

 determination is rendered more certain by the observation of uniaxial character and 

 negative sign in the second amphibolite from this area. 



Gajnet is present, but in most slides protracted search is required to find the small 

 pieces of garnet that may be set in the felspar. A portion of one slide, however, contains 

 considerable garnet. This garnet is very ragged in outline and contains inclusions of 

 felspar, biotite, ilmenite, and a colourless, brightly polarising mineral, probably scapolite. 

 The decomposition of garnet into pyroxene cannot be observed in these rocks in the 

 manner recorded in the Saxon area. 



The relation of the pyroxene-felspar areas to the garnet is difficult to determine 

 in this section. We know they are connected by our study of other sections, and in 

 this instance the aggregate is occasionally replaced by garnet. Scapolite is observed to 

 be included in the garnet and in the pyroxene areas, but it does not seem possible to 

 say whether the pyroxene felspar has been developed from the garnet or vice versa. 



The rock may be described as an amphibolite which is related both to the garnet 

 amphibolites and to the hornblende plagioclase pyroxene gneisses. 



No. 799. The second type of amphibolite from Garnet Point is distinguished 

 from the preceding by a complete absence of the diablastic areas of pyroxene and felspar 

 and associated minerals. 



