96 AUSTRALASIAN ANTARCTIC EXPEDITION. 



may possibly represent the torn-up and diffused remnants of some dyke series, and 

 that they are not to be looked upon as necessarily earlier, without further considera- 

 tion, than the enclosing gneiss. 



In the Loch Laxford to Kylesku area it is stated (p. 134) that gneisses enclose 

 frequent lenticles and lumps composed entirely of hornblende and pyroxene. Again, 

 a leading feature of the Fundamental Complex in the Gruinard district (p. 177) is the 

 extraordinary abundance of knots of basic material in the gneiss. A beautiful, 

 unfoliated diorite is here recorded, but the most abundant consist of the dark hornblendic 

 rock. The same type of thing is observed in other places, and they are looked upon 

 as products of segregation, in common with the acid gneiss, from an intermediate magma, 

 or as included fragments of an older rock system. Now in the Kylesku to Loch Broom 

 area (p. 169) it is found that near areas of dominant stress a dyke may be wrenched 

 into a series of isolated lenticles or " phacoidal masses." The evidence of the Scottish 

 area, apart from the Cape Denison observations, thus shows that a dyke can be torn 

 into fragments which may now appear as isolated inclusions. Hence a complete account 

 of the Scottish Highlands must consider the possibility that many of the hornblende 

 and pyroxenic clots may be the metamorphosed remains of torn-up fragments of basic 

 dykes. They may be stated to be differentiation products caught up in the manner 

 illustrated at Depot Island, South Victoria Land*, by the intrusion of granite, which 

 have been subsequently modified by metamorphic processes ; but there is no positive 

 proof, at present, that requires them to be looked upon as " earlier " than the enclosing 

 gneiss. 



Equally evident as the metamorphic diffusion in the North- West Scottish Highlands 

 is metamorphic differentiation. Rocks are recorded by Teall (p. 45) which consist of 

 pure hornblende, and which are found as knots, lenticles, and bands. Similar separation 

 of the biotite is mentioned in the description of the Loch Maree and Gairloch district 

 (p. 193). Some of these are no doubt similar to the hornblende and biotite patches 

 which have been considered as metamorphic differentiation products at Cape Denison. 



In discussing hornblendites and pyroxenites (p. 45) Teall finds that, by the gradual 

 increase in the amount of hornblende, the pyroxenites pass into hornblendites. They 

 form banded masses, and the possibility must arise as to whether both these types are 

 not metamorphic differentiation types. With suitable metamorphic conditions 

 pyroxene could very well differentiate itself with equivalent result to the hornblende. 

 The recorded section (p. 47), where four hornblendite bands and four pyroxenite bands 

 occur in 4ft. 5in., could well be an example of metamorphic differentiation developed 

 with alternating conditions. It may, indeed, be viewed as a magnified crystallisation 

 schistosity. Where Teall describes the rocks containing hornblende and pyroxene 

 (Group III.B2) he finds that such are related to the pyroxene gneisses. He states 

 (p. 63) that it is impossible to avoid the conclusion that they have been formed from the 



* "Geology." lol. I.. Brit. Ant. Exp., Plate LXXXL, p. 246. 



