THE METAMORPHIC ROCKS OF ADELIE LAND. ST1LLWELL. 53 



porphyroblasts have just commenced to develop a broken granular appearance and 

 show the intermediate stages in the destruction of a large primary crystal. One quartz 

 porphyroblast is a fractured granulitic aggregate, though it still retains its entity in 

 both ordinary and polarised light. In another case fracturing has not occurred, and 

 the central portion of a porphyroblast still shows unbroken strings of linear inclusions, 

 though incipient granulitisation appears between crossed nicols. These strings run 

 diagonally across the plane of schistosity. The section is elliptical and the ends of the 

 longer diameter consist of a granular interlocking quartz aggregate in which each grain 

 possesses different optical orientation. It is an excellent example of the result of 

 solution at the points of maximum pressure with simultaneous deposition at the points 

 of minimum pressure in the plane at right angles to the direction of pressure. In the 

 fractured quartz porphyroblast secondary minerals like chlorite, epidote, and calcite 

 now appear along the fractures. The felspar porphyroblasts are also elliptical. Their 

 calcic nature is evident by the saussuritic products in which chlorite and epidote are 

 definitely recognisable. The centre of one porphyroblast is a granular aggregate, 

 produced by the breaking down of the primary felspar, which consists chiefly of clear 

 secondary felspar with lower refractive index with some epidote, chlorite, and calcite. 

 The remainder of the felspar porphyroblast, apart from the granular nucleus, has also 

 suffered decrystallisation and now presents a " peg " structure. Small rounded blebs 

 of secondary felspar appear in contrast to the primary felspar in polarised light. 



These porphyroblasts of quartz and felspar are set in a much finer granoblastic 

 aggregate of quartz, clear felspar, and saussuritised felspar with sporadic grains of 

 magnetite and pyrite, epidote, chlorite, hornblende, and sphene. The typical grain 

 is here elongated in the direction of the schistosity, giving evidence of a certain amount 

 of crystallisation schistosity. Idioblastic crystals of apatite are included in the quartz. 

 Besides the granular individuals of saussurite in this section there are lenticles of 

 saussurite from a neighbouring saussuritic meta-xenolith. The cloudy appearance 

 has occasionally disappeared and there is left a mass of epidote and chlorite. Some 

 of the layers, rich in saussurite, can be traced directly into the enclosing amphibolite, 

 and some contain sphene and hornblende. 



The gneissic meta-xenoliths, therefore, possess characters which are essentially 

 foreign to the amphibolite host. They possess affinities to the surrounding gneiss 

 though they seem to show a slightly greater degree of recrystallisation. 



Origin of the Meta-xenoliths. 



1. Saussuritic Type. The individual variety of saussurite inclusions have been 

 derived from the decomposition of a felspar. The primary felspars, particularly those 

 with crystal outline, may have been phenocrysts of intra-telluric origin brought up with 

 the injection of the dyke magma. But the presence of the angular and rounded masses 



