\IKTA.Moi: I'll lr I.IMKSKiNKS TII.I.KV. 243 



In these rocks pure maguesiuiu-iiluminiiuu silicates do not occur. Of these 

 latter. conlierite and pyrope garnet are the types. Cordierite is unkno\vn amongst 

 metamorphosed carbonate rocks, and is unstalile in tin- presence of inonoclinic 

 pyroxene, (Joldsrhmidt (') (Considers th.it, its absence mav lie attributed to a reaction 

 of the form - 



.M.L'.Al t Si,0 18 +2CaMgSL0 = 4.MgSi(>,+ 2<'aAl .Si.O., + Sin. 



yielding enstatite or hypersthene, as in the limestone contact zones of the < 'hristiania 

 region. A rhomliic pyroxene is, however, wholly wanting in these Antarctic rocks, as 

 in the product of other areas of regional metamorphism. In this respect the meta- 

 morphism in the Christ iania region may he regarded as the ideal thermal type 

 unaccompanied by any notable shearing stress (-). 



In the rocks now studied, the alumina of potential cordierite is represented in 

 plagioclase, and the magnesia in monoclinic pyroxene.( ) According to Eskola (*) 

 garnets containing more than 75 molecules per cent, of pyrope are unknown, and even 

 these are confined to eclogitic rocks, and unknown amongst metamorphosed dolomites. 

 In this respect pyrope and grossularite differ widely in their paragenesis. 



Throughout this suit of rocks quartz is stable in the presence of calcite. Even 

 in the carbonate-free calc-silicate rock (No. 128) there is no development of wollastonite. 

 The application of Xernst's heat theorem to the equilibrium 



+ SiO. < 'aSiO, + CO 



., 



gives a PT curve which rises with the pressure. Kor aluminous and ferromagnesian 

 lime silicates the corresponding curves, as Uoldsehmidt () has pointed out, run at less 

 elevated temperatures. 



Whilst these more complex silicates (epidote, tremolite, pyroxene, Arc.) were 

 abundantly produced, the development of wollastonite the high-water mark of 

 metamorphism in calcareous sediments was not attained. 



1 V \! lloliU. Imiiilt. \'iri,-ii-.k. Skrift.-r. IHII. X.. 1. p. I3S. : A. Miiikn. l'r,-. A.hl..^ Geo. S.H .. UHs. p I. \\VIII 



* C!.'.,|. Ma.. vol. Ivii. l!l-'ll. |.. 4!Mi. ' I'. Kxk..lu. \,,rsk. (Jrol. Ti.lMkr. \1. n. 172-X 



V. \l. lHiMdiniilt. Vi.li-n-k Skiifln. l!Hl'. X... L'2. p. li. 



