130 MB. C. E. "LLZT :y the GB-I^TITE-GSTEISSIIS [ToLlxxTii, 



With regard to this Lewisian area. Sir Jethro TeaH &: Sir Archi- 

 bald Geikie,! and later Dr. A. Harker,- have drawn attention to the 

 features developed in the Tertiarr gneisses of Skve and Knni, 

 where in the fiist-named heterogeneity has arisen from imperfect 

 differentiation, and in the ^scond masses of gabbro have Y-rz. 

 inTolved in the succeeding acid granites. Snch processes : - r- 

 revealed in these TertiaiT gneisses, where the history of t r _< 

 can be studied more accurately, must be of fruitful appli ; ~ 

 those older formations where onlv the latest stasiies of reac : . i 



interaction are the risible remnants from which conclusi* ::^ m sr 

 be drawn. The sequence of events as disclosed in the L: ~ i 



the much younger plutonic activity, adds confirmation to t r r ^ 

 that in the basic members of Arcbsean gneissic tracts t. t " t- 

 spread disruption of an earlier consolidated phase i 



the same plutonic cycle) is laid bare. An interprets Ii-'Q l-i tiA^r 

 distinction between the Lewisian tract on the one hand and the 

 Ontarian (and we may perhaps add tbe Syrian) region on the 

 other ; the more complex intermingling of basic and acid members ; 

 and the resultant hrbridism alreadT remarked in the Lewisian 

 Series, may be a:^orded by the great dominance of the element of 

 powerful lateral pressure accompanying the Lewisian irruptions, 

 and the intrusion of the Ghatarian and Syrian granites under the 

 influence of mucb simpler mecbanical forces. 



It may be asked, however, bow far these distinctions are a 

 function of the depth of erosion of the particular region, whether 

 with increasingly lower levels of such a formation exposed to view, 

 an increasingly more complex intermingling of earlier and later 

 members, and a greater d^jee of hybridism, stand revealed f 



W. H; wcHisr. Proc Eoj. Gecgr. Soc AnstEalia (S. Anstr. biaiid) 1907, 



pr-. 204-19. 

 I>. 3lIwso>-. Trams. Bojr. Soc. S. Ansl^. voL tt tj (1907) pp. 71-76. 

 E. L Jack. BoIL GeoL Sorr. S. Ads^. 3fo. 1, 1912. 

 L K- Wabd. Ibid. Ko. 2, 1913. 

 E. L Jac^ n^^d. Xo. 3. 1914. 

 A TV^z 7y.:. Xq. 4. 1915. 

 i Z TiizT r :r r i?20, pp. 4i9-€2, 492-500. 



Id. • IjOOhqe:^ : .-- .:^-—. Ir-l. tr . I*-4— '??. 



(1) Granites ^ : re-gneisses : I: ■ _i : ;: ^^r : :- a 



large j:': :::::"- z -rht -:^^-t:_^-t: :. t..;:':! Zt: r r t:;::;-;^:. 

 These :^_:r--;T- "t: T :::^: : ..r - ::/: . -y. ; ..-r serie- _i : : ; .:-. ~\.r 

 Mutchisoii Sen— iri— :t- i . :: :r : z r .. 



(2) The petr — 1-: i r 



tites ai. . :„^ _ Tr- :s 

 blende-biotite. 



isses, pyroxene- 



» Q. J. G. S. ToL 1 (1894) pp. M^-59. 

 3 Ibid. tqL lix (1903) pp. 207 et seq^. 



