GEOLOGY AND PETROLOGY OF ENOGGERA GRANITE. 127 



lying dark rock iiiav, as the result of heat or pressure 

 changes, have become molten again and have been forced 

 up into the cooler overlying Pink Phase as intrusions. 



The field evidence thus appears to indicate that the 

 two phases are not the result of diiferentiation in place, 

 either by gravitative or other methods, and that the Pink 

 Phase is younger than the Grey, and that, further, the 

 aplitic and sandy granites are later than the more normal 

 type of the Pink Phase. Thus we see that the order of 

 ■succession is Grey Phase followed by typical Pink Phase, 

 which in turn is followed by the aplitic and "sandy" 

 granite types of this phase, with finally a reversion to the 

 basic or Grey Phase. This is the order of primary 

 ditferentiation of Brogger, who, to quote Harker, believes 

 in "an order of increasing acidity with in many instances 

 a final reversion to basic types. "^ 



It is interesting to note that this relationship is strictly 

 .analogous with the sequence of intrusions in New England, 

 the ^Moreton district of Southern Queensland, and that of 

 Charters Towers of Northern Queensland, but more detailed 

 ■comparisons with these areas are made later in the paper. 



The following rock analyses give a general idea as to 

 the chemical relationships of the two phases. Analysis El 

 is that of a rock selected as typical of the Pink Phase, 

 while Analysis E4 is that of a rock typical of the horn- 

 blendic type of the Grey Phase. Analysis E2 is the only 

 other analysis from the area and is that of the "Enoggera 

 Granite" used largely as a building stone, and which 

 mineralogically presents important points of similarity with 

 both phases. Analysis E3 is that of the ^Mountain Camp 

 rock, a few miles to the north of Enoggera. 



The precise position of E2 and its relationship to 

 the Pink or to the Grey Phases is a ciuestion about which 

 the author has long been in doubt. In appearance it 

 resembles neither a typical granite nor a typical grano- 

 diorite. The grey colour, the relative basicity of the 

 plagioclases, the absence of pink orthoclase and the 

 abundant pyrites were all points in common with the Grey 

 Phase, but the high acidity of the rock and the marked 



'^ Eruptivgesteine des Kristianiagebietes, " II. (1895), pp. 165-181. 



