Lady Rachel McRobert — A Nepheline- 8 yeiiite Boulder. 3 



inclusions of apatite, and generally surrounded by a green rim of 

 pyroxene. In some instances it forms the nucleus of crystals of 

 segirine-augite, surrounded by hoi'nblende. It is restricted to portions 

 of the slide rich in these. Some of the iron-ore seems to be titaniferous, 

 and in one instance shows alteration to leucoxene. 



Apatite is abundantly scattered throughout all the minerals in small 

 crj'stals, usually taking the form of elongated needles. 



A consideration of these minerals and their association leads one to 

 assign this specimen to the foyaite type ; the percentage of potash- 

 felspar is high and slightly exceeds that of the nepheline. The ferro- 

 inagnesian minerals are of minor importance, their chief constituent 

 being an amphibole, so that this rock may be added to the comparatively 

 restricted list of Amphibole Foyaites, and as yet none of these have 

 been recorded from the Atlantic coasts. 



In this basin some of the most noteworthy occurrences of nepheline- 

 syenites are in the Sierra de Monchique (Portugal) (3), in the Lange- 

 sundsfjord (Southern Norway) (4), at Julianchaab in Greenland (5), 

 at Salem, Essex Co., Mass. (6), and Beemerville, N.Z., and in Assynt, 

 Sutherland (7). 



The specimen under consideration seems to have very little afSnity 

 with any of these. One essential difference from the rocks in Portugal, 

 Norway, and Salem, Mass., is, that these are all pyroxene foyaites. 

 The boulder further differs from them in the absence of biotite, and in 

 the case of the last-named one, in the absence of zircon and eudialite. 

 It shows none of the peculiar radial structure so marked in the 

 pegmatite of Laven, Langesundsfjord, and of the harbour at Salem. 

 The possibility of its migration from Greenland is minimized by the 

 completely different character of the rocks from Julianchaab, described 

 by Ussing, up to the present. He distinguishes three chief types — 



(«) A sodalite - syenite, in which sodalite is embedded in tiny 

 idiomorphic crystals in felspar, nepheline, eudialite, and segirine alike. 



(5) A foyaite type, coarse-grained and composed of eudialite, 

 microciine, microperthite (in broad plates), nepheline, segirine, 

 arfvedsonite, and a little sodalite. 



(c) A fine-grained variety with narrow felspar laths, acicular 

 segirine, and much iron. 



The melanite-bearing rock from Loch Borolan is too well known to 

 I'equire description, and it is evident that the boulder in no way 

 resembles it. 



CONCLTJSION. 



• The outstanding characteristics of the nepheline-syenite boulder here 

 described are thus : its great freshness, the restricted number of its 

 minerals and their normal habit, the prominence of hornblende, the 

 complete absence of all rare minerals such as are so commonly found 

 in nepheline-syenites, and the presence of a fair amount of iron-ore, 

 although the rock is by no means very basic. It cannot at present be 

 compared with anj" known syenite of the North Atlantic basin. 



Eefeeences to Liteeatuee. 

 (1) Hjoet, J. "The Michael Sars North Atlantic Deep-sea Expedition, 

 1910 " : Geogr. Journ., xxxvii, 4, 5, 1911. 



