THE MBTAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 55 



Analogous Occurrences. 



Xenoliths have been frequently reported in normal dyke rocks, and a summary 

 of a number of such occurrences in Europe and America has been recently made by 

 Powers*. Xenoliths in dykes which are now represented by metamorphic rocks, are 

 much less frequent. Flettf has recorded examples from the Lizard district where 

 dykes of gabbro schist and gabbro pegmatite contain inclusions of serpentine, and where 

 epidiorite dykes contain inclusions of red granite. 



I am not aware of the recognition of xenoliths within amphibolite dykes. In 

 Beinn Lair and Meall Mheinnidh, of the Loch Maree and Gairloch District, C. T. CloughJ 

 has reported certain zones of hornblende schist which contain lenticles of a dirty white 

 opaque susbstance which Teall identified as saussurite. A considerable number of 

 these lenticles are more than 1ft. long, while some exceed 3ft. Their long axes lie 

 parallel with each other in some patches, while in others they do not. The long axes 

 are independent of the foliation of the schist. The lenticles have an irregular 

 distribution, and an isolated instance is recorded at a distance of 60yds. from any 

 others. Clough, finding difficulty of explanation, decided that they more probably 

 represent concretions in an igneous rock before its conversion into schist, and that 

 they may have been originally nearly spherical and analogous to spherulites. 



It is quite likely that this occurrence in Scotland is analogous to the occurrence 

 of saussuritic meta-xenoliths at Cape Denison. There is no marked angularity of the 

 fragments in the Scottish instance, neither is there more than one type of fragment 

 recorded, nor is the dyke-like nature of the host obvious. Nevertheless it is quite 

 possible that the Scottish saussurites were cognate xenoliths brought to their present 

 position by an invading magma before the development of metamorphic action. From 

 quite independent sources Clough considers that there is little doubt that the 

 hornblende schists were intrusive rocks. 



7. THE ORIGIN OF THE AMPHIBOLITE SERIES. 



We have now presented the field, microscopical, and chemical characters of the 

 amphibolite series, and we may now summarise the evidence bearing upon its origin. 



Field Evidence. In the first instance field observations strongly suggested that 

 this suite of rocks constituted a parallel system of intrusive dykes. The uniform width, 

 the frequent sharp line junction, the linear trend, and their persistency are valuable 

 criteria. Fresh from the study of a parallel system of dykes|| the likeness to such was 

 found to be highly suggestive. Bulges or swellings in the dyke channels had been 



" The Origin of Inclusion* in Dyke*," 8. Power*, Journ. Oeol., vol. 3, p. 1. 



t " The Geology of the Lizard and Meneage," J. 8. Flett ft J. B. Hill, Mem. Geol. Burr. Gt. Britain, Sheet 359, 1912, 

 pp. 94-128. 



J " The Geological Structure of the North-Weit Highlands of Scotland," Mem. Geol. Surv. Gt. Britain, 1907, p. 243. 



{ Op. cit., p. 240. 



|| " Preliminary Note* on the Monchiquite Dykes of the BendiRo Gold Field," Proc. Roy. 8oc. Viet,, 1911, p. 1. 



