THE METAMORPHIC ROCKS OF ADELIE LAND 8TILLWELL. 61 



and No. 630 was picked up not more than 2yds. or 3yds. away from it. Unfortunately 

 there is no example of this schliere in the rock collection, but it is quite certain from ite 

 soft character that it contained a large percentage of biotite. Another specimen (No. 

 630A), however, was obtained from this spot which is also of curious composition. It 

 is coated with black biotite, but it is hard and contains a good deal of felspar. The rock 

 is not of such even composition as the biotite hornblende schist. The felspar occasionally 

 appears as a porphyroblast, or tends to aggregate and form lighter coloured patches. 

 The mineral composition of the ground mass of this rock, determined in a section cut 

 at right angles to the schistosity, is 



Biotite 44-4 



Felspar 51-8 



Epidote 2-8 



Apatite 1-0 



Sphene and magnetite present but less than !. 



The rock is, therefore, essentially an aggregate of biotite and felspar. The specimen 

 shows a certain amount of mechanical deformation, but this again is subsequent to 

 the development of the biotite and felspar. Some of the biotite is twisted and shows 

 attrition, while some of the felspar is granulated. The felspar is andesine, and a portion 

 is saussuritised. This saussuritisation may have developed in the subsequent crushing. 

 The epidote crystals commonly contain a core of allanite. Quartz is absent. The 

 mineral composition bears some resemblance to that of the band No. 153 (Table I., No. 1). 

 In this case there is no hornblende or sphene and less epidote but more felspar and 

 biotite. We can, therefore, picture its chemical composition with more silica and 

 alkalies and less FeO, MgO, and CaO than No. 153 (p. 21). It is thus certain that the 

 composition of No. 630A, as well as the composition of the biotite hornblende rock No. 4, 

 differs considerably from that of the normal amphibolite. The conclusion is unavoidable 

 that there has been a rearrangement of chemical composition during metamorphism. 



The composition of No. 630, the supposed normal rock of this band, is also 

 abnormal. Table I., No. 6, shows that the colourless constituents in No. 630 are double 

 those in No. 412, an example to which it is otherwise strikingly similar. This large 

 excess in No. 630 is due to the numerous grains of clear, uncrushed quartz, a mineral 

 which is nearly absent in all the normal bands. The microscopical structure of this 

 quartz is essentially different from the quartz in the adjacent granodiorite gneiss. 

 Whereas the latter shows abundant cataclasis, strain polarisation, and participation 

 in the mortar structure, the quartz in the amphibolite is perfectly clear, uncrushed, 

 and with strain polarisation weak or absent. In other respects the minerals in No. 

 630 are similar to the minerals in the biotite amphibolite, No. 412. The abnormal 

 percentage of quartz seems to me to be connected with the abnormal formations of 

 the biotite hornblende schliere and the biotite felspar rock. From evidence which will 

 be given later, we might look upon the biotite felspar rock as a metamorphic hybrid 

 produced by the intermingling of gneiss and amphibolite in the solid state, because a 



