48 AUSTRALASIAN ANTARCTIC EXPEDITION. 



characteristics of mineral and rocks necessarily cause the features of one zone to encroach 

 in varying degrees on an adjacent.* The abundance of biotite in any of these specimens 

 probably means, therefore, a previous abundance of chlorite. This abundance of 

 chlorite, in turn, means abundant chloritisation of the pyroxenes of the primary diabase, 

 which may have occurred either in normal weathering or in the upper parts of the epi- 

 zone. As, however, hornblende as well as biotite could develop from chloritised pyroxene, 

 the amount of biotite cannot be considered an index of the amount of primary 

 chloritisation. 



6. METAMORPHOSED XENOLITHS (META-XENOLITHS). 



One band of amphibolite (No. 629), outcropping near the centre of the Cape Denison 

 area, is phenomenal in containing a large number of xenoliths.f These xenoliths possess 

 the same metamorphic character as their host, and may be distinguished as 

 " metamorphosed xenoliths." We propose, for convenience, to abbreviate " meta- 

 morphosed xenolith " to " meta-xenolith." 



The particular band appears as a broad bulge, about 4yds. wide, issuing from 

 underneath the ice sheet, and after continuing for about 15yds. or 20yds. it narrows 

 down to a band of average width. The meta-xenoliths are scattered through the whole 

 outcrop, but are most abundant along the western edge of the bulge (fig. 5). They 

 consist of white, grey, pale-green, or pale-pink masses which are never more than a few 

 inches long, and which produce strong contrast in colour to the black amphibolite host. 



There are two distinct types of material among these meta-xenoliths, and they 

 may be distinguished as 



(1) Saussuritic type. 



(2) Gneissic type. 



These two types will be subsequently found to correspond to the cognate and 

 accidental xenoliths of normal igneous rocks. 



1. Saussuritic Type. 



The saussuritic type includes the 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. 



(a) The Individual Type of Meta-xenolith. The meta-xenoliths composed wholly 

 of saussurite} may retain the original outline of a primary felspar crystal. The largest 



* Op. oit., vol. I., pp. 70, 71. 



t We use the term " Xenolith " in the same sense that it is applied to igneous rocks. Grubenmann does not provide a 

 special equivalent in his system of nomenclature for the crystalline schists. 



t The term " Saussurite " is used in the same sense as given by Weinshenck (Petrographic Methods, trans Clarke p 336) 

 and by Flett ("Geology of the Lizard and Meneage," Mem. Brit. Geol. Surv., 1912). 



