THE MBTAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 51 



This mineral aggregate, even apart from the primary felspar, is conclusive that we 

 are dealing with the decomposition products of a highly calcic felspar. The crystalline 

 outline, as far as it is observable, agrees with a felspar. The secondary felspar 

 in saussurite is usually recorded as albite, but the composition of the felspar depends 

 on the conditions under which saussuritisation takes place. The conditions under which 

 muscovite, scapolite, zoisite, and clinozoisite form are not those under which secondary 

 albite can form. Among the minerals identified above, lawsonite and chlorite are 

 unimportant or absent in the best or coarsest crystalline aggregates. 



(b) The Composite Type of Meta-xenolith. The composite type of meta-xenolith 

 is formed of a number of saussurite " crystals " set in a hornblende matrix. These 

 aggregates may have an irregular, rounded, or angular outline which frequently appears 

 macroscopically sharp, but it is not necessarily so. A diagrammatic example of one 

 of these aggregates is given on Plate IX., fig. 3. In this case the boundary is sharp 

 and some of the saussurite masses have preserved the shape of the primary felspar 

 crystals. The coarse grained character of the primary xenolith is here quite evident. 

 A remarkable angular example is illustrated on Plate IX., fig. 2. These two " diagrams " 

 were collected from the lower moraines, which consist almost entirely of local rock, 

 at a point a few yards north of the occurrence in situ. A rectangular example obtained 

 in situ is shown on Plate IX., fig. 1. In all these cases the apparently sharp boundary 

 is actually a line of interlocking saussurite and amphibolite", and the saussurite aggregates 

 throughout the block are set in a mass of interlocking, granular hornblende. In type 

 the saussurite is similar to that described in the individual type of meta-xenolith, but 

 here in the smaller crystals recrystallisation has not been so intense. Further, in the 

 specimens that have been examined, lawsonite and chlorite and calcite are more 

 abundant than in previous cases. In addition, sphene is sometimes found in these 

 aggregates. The hornblende is precisely similar to the hornblende in the amphibolites, 

 and the clusters of granular hornblende may readily represent the decrystallisation 

 products of a large primary augite. 



There is every reason to believe that these composite meta-xenoliths represent 

 the relics of clots of coarse-grained rock of the same composition as the primary dolerite. 

 No minerals, except those which have become recognisable in the saussuritic aggregates, 

 are found in the clots that are not found in the amphibolite proper. The clots consisted 

 chiefly of coarse felspar and coarse augite. The coarse felspar is now a saussurite complex 

 and the coarse augite is now an aggregate of granular hornblende. 



2. Gneisaic Type of Meta-xenolith. 



The gneissic type of meta-xenolith shows considerable variation in colour, shape, 

 and size in the hand specimen. They are indiscriminately mixed with the saussuritic 

 meta-xenoliths. Some examples possess a grey colour and so bear strong resemblance 

 in the hand specimen to the grey granodiorite that surrounds the amphibolite. Other 



