Arthur Holmes — Petrology of North- Western Angola. 271 



corresponds to the distinction in mineral composition between the 

 two rocks. Compared with other riebeckite granites, it is clear from 

 analyses, modes, and norms that the Angola rock is richer in riebeckite 

 than any other granite hitherto described. 



Bockallite. Eockall. 

 p. 297, 1914. 



VI. 



VII. 



VIII. 



H. S. "Washington, analyst. Q.J.G.S., vol. lxx, 

 G. Sarnstrom, analyst. Brogger, 



II. Grorudite. Varingskollen, Norway. 

 Zeit. Erist., vol. xvi, p. 66, 1890. 



III. JEgirine- Riebeckite Granite. Congo, Angola. Arthur Holmes, analyst. 



IV. JEgirine-riebeckite gneiss. Carn Chuinneag, Ross-shire. W. Pollard, 



analyst. Mem. Geol. Surv. Scot., Sheet 93, p. 92, 1912. 

 V. JEgirine- Riebeckite Granite. Zinder. Between Lake Tchad and 



Sokoto. Lacroix, C.R., vol. cxl, p. 22, 1905. 

 JEgirine- Riebeckite Granite. Quincy, Mass. Mean of three analyses 



by C. H. Warren and H. S. Washington. Warren, Proc. Am. Acad. 



Arts and Sci., vol. xlix, p. 227, 1913. 

 Paisanite. Magnolia, Essex Co., Mass. H. S. Washington, analyst. 



Joum. Geol., vol. vii, p. 113, 1899. 

 Riebeckite Granite. Ekona, Sungale, Kamerun. Rosenbusch, loc. cit. 



Corresponding with the high riebeckite content of the rock is its 

 comparative richness in zirconia. The ratio of riebeckite to zirconia 

 in the Quincy granite (analysis YI) is practically identical -with that 

 of the Congo rock. 



Granites containing both riebeckite and aegirite or acmite are 

 somewhat rare, and in addition to the four examples of which 

 analyses have been quoted the only others of which I have 

 succeeded in finding a record are from the following localities : — 



