PETROLOCICAL NOTES ON FURTHER ROCK SPECIMENS, 



COLLECTED FROM IN SITU OCCURRENCES. 

 COMMONWEALTH BAY REGION. 



BY 



J. O. G. GLASTONBURY, B.A., M.Sc. 



WITH TWO PLATES. 



I. NOTES ON FURTHER* SPECIMENS FROM THE METAMORPHOSED DYKE 



SERIES OF CAPE DENISON. 



1. INTRODUCTION. 



" ONE band of amphibolite, outcropping near the centre of the Cape Denison area, is 

 phenomenal in containing a large number of xenoliths. There are two distinct types 

 of material among these meta-xenoliths, and they may be distinguished as 



(1) Saussuritic type ; 



(2) Gneissic type. 



The saussuritic type includes pale green and pale pink masses which may be 

 again subdivided into 



(a) Those composed wholly of saussurite the individual type. 



(b) Those composed of an aggregate of saussurite and hornblende the composite 

 type." (Stillwell : Series A, Vol. Ill, Pt. 1, p. 48.) 



This statement of StillwelTs is given because the rocks to be discussed here 

 (Nos. 142, 421, 432, 632, 633, 635A, 666 and 1240) are all members of the dark 

 amphibolitic series found in situ at Cape Denison. 



No. 421 is the coarsest of the set. As seen in the hand specimen it consists of 

 handsome blades of black hornblende set in a base of coarsely crystalline opaque felspar. 

 Its structure is gneissic. 



Nos. 432, 666 and 1240 are examples of the amphibolite xenoliths containing 

 porphyritic saussurite individuals. They are of " The individual type of meta-xenolith " 

 variety according to Stillwell's classification. 



No. 142 is another of the individual type of meta-xenolith, but owing to the few 

 phenocrysts of saussurite and the definite schistosity it has taken up it seemed well to give 

 it a further description. 



*Dr. StiUwell's original report deal* with outstanding examples of the dominant type* of rock* met with in *ilu. 

 Rocks described in thU contribution are, in the main, closely similar to example* selected and described by Stillwell. The 

 present descriptions are supplied in order to render more complete the microscopical examination of the whole of the 

 rock collection. P.M. 



