from Krageroe, Norway. 513 



Calculated in the usual way from the chemical analysis of 

 the rock given above, the composition of the feldspar content 

 corresponds to : 



Or 6-12 



Ab 52-40 



An. __ 5-56 



Ab n An m ratio 9-4:1 =47:5 



Or-Ab„An m ratio 1:9-5= 5:47 



Total plagioclase 57-96 



Total feldspar 64-08 



A noteworthy feature of the rock as indicated in the 

 analysis is the unusually large percentage of Ti0 2 , which is 

 present chiefly as rutile and in very small quantities as ilmenite 

 and leucoxene. The high Na a O, which greatly exceeds K 2 Oin 

 • amount, and the low CaO confirm the microscopic study of the 

 composition of the principal feldspar as corresponding to a 

 sodic plagioclase of the albite-oligoclase series. 



The norm as calculated from the analysis and the position of 

 the rock in the quantitative system are as follows : 



Norm. Eatios. 



Q... 7-62 Sal 72-31 , 



r»,. «.io Class, •= — = = 2-7 = 11, dosalane. 



° 1 -- 6 12 'Fern 26-66 ' 



Ab . 52-40 



An. 5-56 Order "=^ 2 • 



C... 0-61 Sal = 72-31 ' F 64-08 



Jty- °'®° n „ KO + Na,0 111 domalkalic, 



Hm. 0*48 



Ru . 25-04 



Order, -^ = a a ^ = 0-12 ='5, germanare. 



I\ ■' I ■:- : ; .1 ' " III (!( Ill 1-1 I I. '-I I l<: , 



Hm. 0-48 R ang) ^__^ = _ r=5 -5= ' 2 = mon _' 



„ „ zonase. 



Pr.. 0-24 , K„0 11 



H a O 0-50 Fera = 26-66 Subrang, ^^ = — = 0-11 = 5, persodic. 



QQ-47 ~ , P+O 0-90 



Grad, - ir = 2T ^ = -03 = 5, permitio. 



„ . H 0-48 



section, ^ = = -02 = 5, no name. 



' T 25-04 



As indicated above, the norm places the rock in the dosalane 

 class, in the germanare order, in the domalkalic rang monzonase, 

 and in the persodic subrang. Because of the unusual composi- 

 tion of the rock, to whieh attention has been directed in the 

 analysis, it is necessary to further subdivide into grad and 

 section. This subdivision, which shows up the peculiar com- 

 position of the rock, places it in grad 5 (permitic), and section 5. 



The subdivision on ff, which places the rock as a section of 



grads 4 and 5, is not provided for rocks in class II (dosalane) 



Am. Jour. Sci.— Fourth Series, Vol. XXXIV, No. 204. — December, 1912. 

 34 



