32 | ARCTIC BASALT PLATEAU 
projection in the a—c—f-triangle lies on the a—f side. The actual 
composition („mode“) as calculated on base of the analysis and the © 
quantitative estimation given above is tabulated as follows, with the 
following modifications against the optical statements, namely that 
1/ all TiO, is forming perofskite (it was supposed, that the magnetite 
contains small quantities of TiO,, and that the augite is titaniferous); 
2/ that the leucite forms an independent generation in the ground- 
mass and that the composition of nephelite and leucite is an ideal 
one (no absolute certainty hereupon was given). The overplus of 
soda over the aequivalent of alumina, after nephelite and analcite 
(on base of H,O) calculated, was checked as acmite molecule be- 
longing to the augite; and the olivine: augite proportion was calcu- 
lated on base of resting FeO+-MgO-+MnO-content, i. e. the 
hyalosiderite composition of olivine and the remainder of SiQ,. 
Mie AS Weight Volume 
percentage percentage 
Olivine REN nace BE ARE NS 22.091 495 46.8 
ISIE Ie Wren EEE RN 27.725 27.4 
NepHelite ses... Cece ou Acts i Ue ee NE 21.50 25.0 
NEUERE je ke rr ls occ bee alot be ro IRMA RSA ie 142] 37.85 ia} 45.2 
ANT CEN ChE a SNC aya kilo shy EG he Oh a) Rae ems 2.08 2.9 
IVIG GTI ULE ees RN RB, settee eee e eee et Ting re 5% 
Peroiskiteng a ren al RN IR 3.95 3.0 
DAUER NE NE ae Aes MPSS EN a ON 2.73 2.6 
99.55 99.6 
SPEAHEIOTAVILYSHEL. Mur en SER NS LIGA 3 045 — 
x ri GA LC een De ole 4 Va eeemionag — 3.042 | 
A comparison of the figures found by measuring and calculated 
gives a good concordance; a calculation of the lenads (except 
analcite) as extremely potash bearing nephelite, with a composition 
as for instance found in the sodalite-syenite of Kangerdluarsuk 
(Greenland) by Lorenzen,* or produced experimentally by Ch. and 
1 A. Lorenzen, On minerals from sodalite-syenite, Greenland. Min. Mag. 5. 
1883. p. 60. 
