GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 483 



Chemical Composition. The following is a bulk analysis 

 of a part of this specimen kindly made for us by Mr. 

 Mingaye ; and we set beside it for comparison the analysis 

 of the essexite of Brandberget, Gran, published by Brogger 

 in his paper on the Basic Eruptive Rocks of Gran : — 



I. II. 



Si0 2 41-05 43-65 



Al 2 O s 12*27 11-48 



Fe 2 O s 6*39 6*32 



FeO 11-07 8-00 



MgO 6*38 7*92 



OaO 10*96 14*00 



Na 2 2*43 2*28 



K 2 0*53 1*51 



H 2 4-02 I'OO 



Ti0 2 4'39 4-00 



I. Essexite of Prospect (Specimen I). II. Essexite of 

 Brandberget, see Q.J.G.S., vol. 50 (1894) p. 19. 



The two analyses closely resemble one another, but of 

 the two the Prospect rock is evidently much the more 

 decomposed. In the part of the mass from which this 

 specimen came it also contains more ilmenite and less 

 biotite than the rock of Brandberget. Compared with 

 normal essexites, the Prospect rock is poor in alkalies, and 

 richer in lime and magnesia. It is also poor in silica and 

 alumina, and rich in ferrous oxide. These latter differences 

 are easily accounted for by its much higher content of 

 ilmenite and magnetite. The analysis also agrees closely 

 with those of olivine-gabbros and olivine-dolerites, allowing 

 for a deficiency of labradorite in the Prospect rock, and of 

 its ilmenite. 



Specimen T (Univ. of Sydney Coll., No. 2154) 

 Locality. About 40 yards from the N.W. end of the 

 Reservoir Quarry, that is, a few yards beyond the left end 



