Vol. 59 .] 



THE TIREE AND IONA MARBLES. 



99 



Carbonates. — In most cases ealcite is the predominant car- 

 bonate : it is rare for dolomite to be abundant. The deformation and 

 granulitization of the carbonates are referred to above. Heddle ] 

 gave the following percentage analysis of Tiree Marble : — 



CaC0 3 =95-94; MgC0 3 = T78; FeC0 3 = 0*576; MnCO 3 =i-028. 

 Pyroxene. — The Tiree Marble has always been noted for its 

 w coccolite.' This mineral (which is not more characteristic of the 



Fig. o. — Crush-conglomerate on the shore west of Port Abhuinn : 

 mylonized limestone with yneiss- inclusions. 



Ethel M. Coomuraswiiniy photo. 



pink Balephetrish marble than is amphibole) appears to vary in 

 colour from light to dark green, nearly black, the latter colour 

 being characteristic of the mineral- aggregates, composed of pyroxene, 

 scapolite, sphene, and blue apatite. I have in this paper spoken of 

 the coloured pyroxene associated with the marble as coccolite, and 

 called the white pyroxene sahlite, as this name has been employed 

 by previous authors. Masses of sahlite form large and small augen 

 in the white marble in the field south-east of Ealephetrish Hill. 

 An analysis of sahlite by Heddle J is here quoted : 



SiO 2 =50-54; Al.,0 3 =469 ; Fe.,0,=4T4; FeO=O04 ; MnO = 069; 



Cad=23-59; a Mg6 = 14-4; K.;O = 0:Jl ; Na.,O = 0t>3 ; H.,0 = T48. 



Total = 100-51. 



Heddle appears to classify all the pyroxene as sahlite, as he says 



1 'Mineralogy of Scotland' vol. i (1901) p. 137. [Mr. E. C. C. Stanford 

 gave analyses of Tiree Marble, Eep. Brit. Assoc. 1870 (Liverpool) Trans. Sect. 

 p. 65.— En.] 



2 Trans. -Roy. Sue. Eclin. vol. xxviii (1870; p. 460. 



