130 PROCEEDINGS OF THE ROYAL SOCIETY OP QUEENSLAND. 



If, then, the rock is a hybrid, we might expect it tO' 

 betray its mixed origin more directly in its chemical com- 

 position. The most remarkable feature of the Analysis E2 

 is the practical equality and low values of CaO, Na^O, and 

 KoO. In this combination the analysis differs markedly 

 from all the analyses of average acid plutonic rocks com- 

 piled by Clarke, Daly, and Osann, to which the author ha& 

 access. Further, a search was made through the ninety-six 

 analyses of rocks placed in the same subrang (Tehamose) 

 in Washington's ''Superior Analyses of Fresh Rocks" for 

 similar types. 



A noticeable feature of the analyses was the wide range 

 in the absolute and relative values of CaO, Na^O, and K^O, 

 a point to which the author naturally gave much gfttention. 

 One analysis was found which is remarkably close to E2, 

 especially in the alkalies and alkaline earths ; but — and this 

 the author considers very significant — it is not strictly an 

 igneous but a metamorphic rock. It is No. 9 in Wash- 

 ington's list for the subrang, and is described as a granite 

 gneiss from Virginia, U.S.A." 



The analysis next most like that in question is Xo. 2, 

 a Hypersthene Adamellite from Havnef-jord, EUesmere 

 Land, and is patently not a normal granitic type. No. 61, 

 Tonalite Porphyrite, from the Tyrol, and No. 65, Adamellite 

 from Switzerland, approach the Enoggera hybrid in some 

 respects, and a curious series of rocks from Japan, notably 

 the ' ' Granite ' ' No. 79, seems to provide a somewhat similar 

 rock. 



The evidence, on the v/liole, seems to uphold a h.ybrid 

 origin for the Enoggera building-stone. 



It is interesting to note here that Jensen suggests that 

 the Cooroy Monzonite and the Pt. Arkwright Porphyrite, 

 both some 75 miles to the north of Enoggera, are "made up 

 of a mixture of a dioritic magma with the aplitic 

 differentiation product . . . ."** 



Further consideration of this important question of 

 hybridism in the Enoggera area will be given in that 

 portion of the paper dealing with comparisons of the local 

 granitic rocks with those of other areas. 



'"A Description of the Quantitative Classification of Igneous 

 Eoeks," 1918, p. 81. 



* ' ' Geology of the Volcanic Area of the East Moreton and Wide 

 Bay Districts, Queensland. " Proc. Linn. Soc. N.S.W. 1906, p. 132. 



