THE METAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 67 



The calcic felspar has been saussuritised, rarely persisting as a relic. The 

 saussuritisation here is not a simple weathering process. Normal surface weathering 

 is absent in Adelie Land, and the mineral products in saussurite are perfectly fresh, 

 even after exposure at the surface. Members of the epidote family, chlorite, lawsonite, 

 occasional zeolites, a secondary white mica, scapolite, and a secondary sodic felspar, 

 have been recognised in the saussurite. Part of the saussuritised felspar has 

 recrystallised, and in some cases we get clear andesine formed. The pyroxene has been 

 completely changed. It is replaced by clear hornblende in the amphibolites, by biotite 

 and epidote in the biotite epidote schists, and by both hornblende and biotite with 

 associated epidote in the biotite amphibolites. In discussing the zonal changes, it 

 has been considered that the biotite has developed through a chloritic stage, and that 

 the chlorite was derived directly from the pyroxene. It is probable, however, that 

 there was a little primary biotite in the diabase. The amount of mica in the 

 amphibolites is approximately constant, and therefore cannot be dependent on a 

 varying amount of chloritisation of the pyroxene. Further, the chlorite in these 

 members appears regularly in large broken plates, which are sparsely distributed, and 

 which are always penetrated poikiloblastically by epidote, together with clear quartz 

 or felspar and iron ore. Such chlorite can be considered as produced in the 

 decrystallisation of primary biotite*. The primary ilmenite has been altered to 

 leucoxene, which has recrystallised as sphene, or it has decomposed into sphene and 

 magnetite according to the equation given by Van Hisef. It is doubtful whether all 

 the titanium is dissociated from the iron though the occasional presence of rutile rather 

 suggests so. Certainly the larger grains are little magnets. The apatite has remained 

 unchanged. 



Either during or subsequent to the metamorphism fracturing occurred and the 

 fractures have been filled with quartz, felspar, epidote, lawsonite, and calcite. Such 

 epidote and lawsonite, etc., may be subsequent to the epidote and lawsonite in the 

 schists, but cannot be used as an argument to show that all the epidote and lawsonite 

 is formed subsequent to the schistosity. The epidote that takes definite part in the 

 foliation must be considered as a primary metamorphic mineral of the same standing 

 as biotite or hornblende. The epidote percentage has been shown to vary 

 sympathetically with the biotite percentage which, in turn, varies inversely with the 

 hornblende percentage. Further, the biotite or chlorite may be moulded on to perfect 

 crystals of epidote in a manner which is impossible on a theory of subsequent 

 epidotisation. The mineral-filled fractures do show that the rocks have been in a zone 

 containing water. As fracturing may occur under the conditions of excessive stress 

 in the epi zone of metamorphism, and as water may be present in this zone, there is 

 no need to dissociate these minute fractures from the metamorphic characters. 



In this manner, then, a diabase or dolerite containing calcic felspar, pyroxene, 

 biotite, ilmenite, and apatite has been converted into an epidote biotite schist or an 



* Van Hue, " TroatiM on MeUmorphum," Hon. 47, U.S.A. Geol. Surv., p. 341. 

 fOp. oit., p. 227. 



