THE METAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 151 



sediments, now represented by biotite cyanite gneiss, before the recrystallisation, and 

 that the junction between the two has been rendered indefinite by the recrystallisation. 

 It also seems probable that a migration of molecules has taken place across the original 

 boundary during the metamorphism, and the position of the original junction is marked 

 by the mixed rock. It also seems probable that certain simple minerals like quartz 

 and cyanite are able to migrate further than the more complex garnet or biotite or 

 hornblende. We may refer to this as another instance of metamorphic diffusion, and 

 it would be very interesting to see how far this cyanite could be traced into the 

 amphibolites. This we are, unfortunately, unable to do from the material in our 

 collection. The specimens are small, and from them we can only determine that cyanite 

 is found in amphibolite at least an inch from the apparent contact. All the specimens 

 of this dyke show fragments of the attached gneiss. 



Cape Pigeon Rocks. 



Garnet gneisses are recorded in the field notes from this locality, but there are no 

 specimens of it in the collection. The garnets are noted as being particularly abundant 

 in part. A different phase of the gneiss with large porphyritic crystals of felspar is also 

 recorded. Hypersthenic gneisses were collected from this locality and will be dealt 

 with later. 



Stittwett Island. 



A garnet gneiss (No. 917), similar to the garnet felspar gneiss (No. 777) collected 

 from Garnet Point, is obtained from Stillwell Island. The large garnet-mica aggregates 

 are again a feature in the gneiss on the island. The mica associated with the garnet is, 

 in most sections, the pale-greenish variety, from which the brown biotite is only feebly 

 developed ; but in one example (No. 939), collected a little below the summit of the 

 island, the brown biotite completely replaces the greenish variety. The green biotite 

 forms the marginal fringe to nearly every fragment of garnet, and there can be no doubt 

 that the aggregates were originally complete crystals of garnet. Pleochroic haloes are 

 abundant in the green mica, and we notice, again, that the alteration caused by the 

 radio-active particle has caused transition to brown biotite. In such cases the brown 

 biotite emphasises the halo area, and an example has been noticed where only the inner 

 ring of a halo with structure is marked by the brown biotite. 



This specimen shows in part more evidence of cataclasis than the Garnet Point 

 example. Granulation of the quartz, which has developed with the mica from the 

 garnet and mortar structure, are present, though not in any marked degree. Large 

 garnets (No. 9176) occasionally show cataclasis and are then represented by a granular 

 aggregate. The granulated garnet, like the granulated quartz, may be drawn out in a 

 linear manner in the direction of schistosity. The plagioclase is very cloudy, and the 

 diablastic and sieve structures are prominent. Large orthoclase and perthite may 

 be traversed by lines of sericite. Occasionally we find areas of cordierite with its 



