GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 481 



him. In order to separate the augite a part of the rock 

 was powdered and sifted, and the heavier portions (com- 

 prising augite and ilmenite) were separated from the lighter 

 (felspar, analcite, chlorite etc.) by the specific gravity 

 method, Klein's solution (cadmium borotungstate) being 

 used. The ilmenite was found to be easily attracted by a 

 common bar magnet, whereas the augite was not ; accord- 

 ingly these were afterwards separated by a hand magnet. 



About 10*85 grams of augite-ilmenite were treated, and 

 6*9 grams of augite was obtained, leaving 3*95 grams ; 

 that is 63*6% was augite and 36*4% ilmenite. The ilmenite 

 was not quite pure, however, for any augite grains to 

 which ilmenite adhered, or which included ilmenite, were 

 attracted. The augite obtained was pure. 



By the Rosiwal method the proportion of augite uncor- 

 rected for decomposition in this rock (Specimen I) was 

 33*9% and of ilmenite 17*1%. Thus of the total augite and 

 ilmenite 66*5% was augite and 33*5% was ilmenite. This 

 closeness of the relative proportions of augite and ilmenite 

 by the two methods of estimation and consideration of the 

 fact that error crept into the former method, firstly in the 

 sifting, secondly by the augite including or partly embracing 

 ilmenite fragments and thus being attracted by the magnet, 

 gives confirmation of the reliability of the Rosiwal method. 



The following was the result of analysis of the augite: — 



Si0 2 





49*66 



H 2 



0*10 



Al 2 6 3 





5*77 



Ti0 3 



0*10 



Fe 2 3 





5*00 



P 3 5 



0*04 



PeO 





7*10 



MnO 



0*01 



MgO 





13*03 



SrO 



trace 



OaO 





20*78 



v 2 o 5 



0*06 



Na s O 





0*55 



OuO 



0*01 



K 2 





0*11 







Zr0 2 , Or, 



.O a , 



NiO, OoO, 



BaO, and Li 



2 tried for and 



proved absent. 









