Vol. 65.] WITH PORPHYKITIC LABRADOEITE-CEYSTALS. 



The percentage of sinj 

 approximately as follows :- 



components in the ground-mass is 



61 - 88 per cent, plagioclase 

 (52An ; 42Ab, 60r) 



9 per cent, titano- 

 magnetite 



f 

 I 

 13 per cent, hypersthene ■{ 



13 per cent, dialla^ 



32-2 per cent. CaAl 2 Si 2 O s 

 NaAlSi 3 Os 

 KAlSi 3 8 

 Fe 3 4 

 FeTi0 3 



Mg;Si 2 ( ; 



Fe 2 Si 2 G 



CaFeSi 2 6 



FeALSi0 6 



FeFe 2 Si0 6 



CaMgSi 2 0c 



CaFeSi-:0, ; 



Fe 2 Si 2 6 



FeAl 2 Si0 6 



FeFe 2 Si0 6 



126-0 

 I 3-7 



(8-1 

 .1 0-9 

 7-8 

 2-6 

 1-7 

 0-6 

 0-3 

 7-8 

 2-6 

 1-3 

 0-8 

 05 



•8 per cent. Mg 2 Si 2 6 

 CaMgSi 2 6 



4-3 

 39 

 1-4 



0-8 



CaFeSi,O f , 

 Fe 2 Si 2 6 

 FeAlaSiOn 

 FeFe. : SiO a 



3 per cent, biotite ( several components in 



L small quantity. 

 0*12 per cent, apatite. 

 Also about O01 percent, of spinel and about the same quantity of iron-pyrites. 



Chemical composition and mineral percentages of 

 the rock as a whole. — From the cut surface of the big block 

 (see fig. 1 & Analyses 1, 2, & 4) almost a third of a square metre 

 in area, the phenocrysts were drawn on millimetre-paper and 

 the contours further corrected afterwards. On a surface of 

 2400 cm. 2 the phenocrysts represented about 612 cm. 2 , being about 

 25-5 per cent, by volume. Considering the specific gravity of the 

 phenocrysts (2*708) and of the ground-mass (about 3*00), we 

 get the result that the phenocrysts in the present case represent 

 very nearly 23 per cent, of the total weight. In other samples the 

 phenocrysts are sometimes more, sometimes less plentiful. Below 

 we are only concerned with the big block (Analyses 1, 2, & 4). 

 The composition of the whole rock may be calculated as from 

 23 per cent, phenocrysts (No. 1 b) and 77 per cent, ground-mass 

 (No. 4). 



Composition of the Poephyritic Labradorite-Norite 

 (Nos. 1, 2, & 4). 



No. 6. 



Si0 2 48-96 



Ti0 2 1-34 



Al 2 :i 21-27 



Fe 2 Os 4-68 



FeO 5-47 



MgO 4-10 



CaO 10-11 



Na.,0 2-97 



K 2 6 1-16 



P 2 5 0-04 



Total 



100-10 



