132 THE GEAXITE-GXEISSES OF [vol. IxXVU, 



DlSCUSSTOX. 



Dr. A. Wade congratulated the Author upon the thorough piece 

 of work which he had presented. He had spent some time in 

 mapping the area in connexion with a report on petroleum re- 

 sources for the South Australian Government. 



The speaker drew attention to the difficulties under which the 

 Author must have laboured while eno-as^ed on this work. There 

 was great need for further research of this character in South 

 Australia. He quoted, for example, a dome-like mass of granite 

 surrounded by a variety of metamorphosed sedimentaries near 

 ' The Frenchman,' on the western coast of Eyre Peninsula, as 

 also the granites of the southern coast of Kangaroo Island which 

 have broken through and engulfed sedimentary rocks, included 

 portions of which are to be seen in all stages of assimilation and 

 alteration. The speaker could confirm many of the Author's 

 observations, and Avas in entire agreement with him as to the age 

 of the gneisses and associated rocks. 



Mr. J. F. X. Geeex appreciated the close and restrained 

 reasoning of the paper, based on careful observation. He was not 

 sure that the same epithets could be applied to other reasoning 

 that had recently come from South Australia, and could not agree 

 that Mr. Stillwell had definitely proved a dyke origin for the 

 Adelie-Land amphibolites. The E^^re district did not seem to 

 compare well with Haliburton, where there was a special associa- 

 tion of rocks, notablv olio-oclase-o'neisses. varied alkali-svenites, and 

 scapolite-amphibolites, which was repeated with detailed resem- 

 blances in other places, such as the Urals and the Grold Coast ; 

 rather it followed the commoner type found south of Haliburton, 

 where gneisses canwing more basic felspars broke up the Keewatin 

 lavas at the base of the Ontario Archsean series. The occasional 

 preservation of amygdales and ■ pillows ' left no doubt that the 

 Keewatin basic rocks had been lavas. 



This valuable paper added to the growing volume of evidence 

 that orthogneisses w^ere usually not, properly speaking, meta- 

 naorphic at all, but in their original state of consolidation ; and 

 that the chief element in the metamorphism surrounding them 

 was thermal. The drawing of foliation-planes of gneiss curving 

 with the edges of twisted amphibolite was especially interesting, 

 and might be compared with maps on a much larger scale, as, 

 for instance, in the metamorphie areas of Xew York State ; but it 

 should be remembered that the most striking evidence for this 

 view, stronger even than that collected in North America, was laid 

 before the Society twenty-seven years ago by Mr. Gr. Barrow. 



Mr. G. H. Pltmex said that a study of the Pre-Cambrian rocks 

 of the Channel Islands enabled him to appreciate the value of the 

 Author's work. The invasion at Port Lincoln of hornblendites 

 by a gneissose rock closely resembled the banded gneisses and 

 hornblende-schists of Sark. In Port du Moulin (Sark) the latter 

 name was applied to the finer bands and the former to the coarser 



