86 PEOF. J. H. 1. VOGT ON LABRADORITE-NORITE [May 1909, 



The hypersthene occurs in two varieties : the one with weaker 

 interference-colours and less marked pleochroism ; the other with 

 somewhat stronger interference-colours and more vivid pleochroism. 

 The latter variety is, therefore, richer in the ferrous silicate. This 

 variety is occasionally found in belts round the first-named, and 

 is thus of relatively later formation. Both kinds of hypersthene 

 are, judging from their interference-colours and pleochroism, com- 

 paratively rich in silicate of magnesia and relatively poor in silicate 

 of iron. 



Garnet is found in very small quantities, in the well-known 

 zones surrounding the iron-ore, sometimes also round the ferro- 

 magnesian silicates, namely, where these abut against plagioclase. 

 This garnet-border does not belong to the epoch of crystallization, 

 and need not be further considered. 



Chemical composition of the ground-mass and its per- 

 centages of minerals. — In my laboratory two analyses of the 

 ground-mass were made : No. 4 (four very closely agreeing parallel 

 analyses by my students, Mr. C. Carstens & Mr. H. Marstrander) 

 of the large block already repeatedly mentioned (see fig. 1, p. 82, 

 and Analyses !Nos. 1 & 2), and No. 5 (by my student Mr. A. Petter- 

 son) of another sample. 



Chemical Analyses op the Ground-mass op the Torphyritic 

 Labradorite-Norite. 





No. 4. 



No. 5. 



Si0 2 



47-75 

 1-74 



18-71 

 6-08 

 7-11 

 5-32 

 9-47 

 2-70 

 1-20 

 0-05 



46-22 



0-30 



20-18 



| 15-00 



5'75 

 9-38 

 3-31 

 1-29 

 0-19 



TiOo 



A1„0 3 



Fek) 3 



FeO 



MgO 



CaO 



NaoO 



KoO 



PoO, 





Totals ... 



100-13 



(101-62) 



Less oxygen in 



Fe„Os j 



about 

 1-00 





Total (less i 



nFe 2 3 ) { 



about 

 100-62 



No. 5 shows a very little more iron-ore and ferrornagnesian silicate than 

 No. 4 ; and further, the rock, as observed under the microscope, showed more 

 apatite. The determination of titanium-oxide in No. 4 is probably a little 

 too high, and in No. 5, on the other hand, somewhat too low. 



