(noted by Professor David). The ultra basic rocks of the 

 Gundagai district 1 and those of the belt stretching from 

 Nundle to Bingara 2 do not appear to be associated with 

 such a batholith at all. From their great length and small 

 width, and particularly from their parallelism to the strike 

 of the country rock, they seem rather magnificent examples 

 of sills of sima locks intruded along fold lines, as described 

 by Suess. 3 Moreover, all of these instances are three 

 hundred miles or more from Sydney. As a final condition 

 the hypothetical batholith must have a highly differentiated 

 marginal facies at almost every centre of late volcanic 

 activity, to account for the variety of inclusions where 

 these are present in Tertiary ba<alt. or the monehiquites. 

 These necessary assumptions place the existence of such a 

 batholith almost beyond the bounds of possibility. If, on 

 the other hand, we consider the great mass as broken up 

 into small highly differentiated bodies, their non-appearance 

 at the surface and deep seated occurrence in association 

 with centres of eruption suggest their genetic relationship 

 to the volcanic eruptive products. Further we may note 

 that none of the igneous rocks present as inclusions are such 

 as might not have differentiated out from a magma of the 

 composition of their host. 



The Sydney basalts and those of the South Coast are 

 sometimes normally alkali-calcic, sometimes nepheline- 

 bearing. They seem to be the final products of a series of 

 eruptions from a magma which in its earlier stage* u - 

 distinctly alkaline, but succeeding eruptions distinctly less 

 so. ; Reflecting this alkalinity, we have among the series 

 of plutonic inclusions normally alkali-calcic, as here 

 described, a semi-alkaline rock, the essexite of Hornsby. 



1 J. E. Cam.'. Ann. R..*p. Dept. Mines, 1892 and 1895, also P. T. Ham- 

 mond, Rec. Geol. N.S.W. 



" W. A. Anderson, Ann. Rep. Dept. Mines, N.S.W., 1888, p. 170. 

 3 The Far- of ri,. E irth, - I »' translation, Vol. iv, p. 564, 1909 

 ' J. B. Jaquet, and G. \V. Card, op. cit. supra p. 66. 



