THE METAMORPHIC ROCKS OF ADELIE LAND.-STILL\VELL. 177 



index above quartz. This is labradorite, but I think the bulk of the felspar has a refrac- 

 tive index below quartz and a small extinction angle. There is a little pyroxene present, 

 but there are still good examples of the pyroxene-felspar vermicoidal intergrowths. 

 These intergrowths may extend as a bite into a garnet crystal, but it may be interpreted 

 either as a breaking down of the garnet or as a patch of unformed garnet (Plate VIII., 

 fig. 1). It may form a zone around ilmenite crystals in the manner suggested in No. 935 ; 

 and as the ilmenite crystal may be embedded in garnet, the pyroxene-felspar interlacing 

 may form an annulus between the ilmenite and the garnet (Plate VIII., figs. 2 and 3). 

 The pyroxene " fingers " are often radial, both to an ilmenite nucleus and to a garnet 

 nucleus, and then a " centric structure " is formed. The hornblende has developed 

 from the pyroxene, and we sometimes find the normal pyroxene " fingers " of the inter- 

 growth converted into spokes of hornblende ; more rarely we find spokes of biotite. 

 Sometimes we find the intergrowth embedded in a crystal of hornblende. 



A large individual of ilmenite is often a network rather than a compact mass, and this 

 is due to the imperfect coalescence of the small primary ilmenite crystals. Occasionally 

 the ilmenite network is set in a pyroxene base, and this is clear evidence that it is due 

 to the aggregation of minute inclusions in the primary augite, in the same way as was 

 observed in several sections. In all cases here this pyroxene-felspar intergrowth, which 

 we have included as a diablastic structure, may be explained on the hypothesis of the 

 interaction between pyroxene and anorthite to produce garnet and quartz. This reaction 

 is, doubtless, reversible. It has proceeded in the direction of the garnet in this example ; 

 but there is no reason why it should not proceed in the reverse direction in certain 

 examples in which garnet is said to be disappearing.* The abundant quartz accom- 

 panying the abundant garnet is clear evidence that Si0 2 is separated in the reaction. 



The size of the garnet crystals is large in comparison with that of the garnet crystals 

 which form the garnet rims in No. 935. This can be readily explained as being due to 

 the growth of larger garnets at the expense of smaller crystals, a phenomenon which 

 has been exemplified by the hornblende in the Cape Denison series, and which will 

 subsequently be exemplified by the pyroxene in this series. 



The rock is described as a garnet amphibolite. The felspar of the normal 

 amphibolite is here partly replaced by garnet. 



Cape Pigeon Rocks. 



Several dykes of basic rock exist on this locality. The obvious nature of the dykes 

 is recorded in photographs. Two large dykes (Plate XXVII., figs. 1 and 4) cut obliquely 

 across the foliation and are upwards of 30ft. wide. There are numerous smaller ones 

 as well (Plate XXVI., fig. 4), and some are only Sin. wide. 



No. 767. Specimen No. 767 is an example of the large dyke. It is a dark, fine- 

 grained rock in which a faint schistosity may be detected. The schistosity is recognisable 

 in the slide, and there has been complete recrystallisation of the primary dolerite. 



* " Untorauchungen die AltkrutaUiniwhen Sohiefergwtoine," Lehmann, Bonn, 1884, Tafel XXIV., fig. . 

 Series A, VoL ni.. Part 1 M 



