310 G.W. Tyrrell — Bekinkinite of Barshaw, Renfrewshire. 



and in which barkevikite is a prominent constituent as well as augite. 1 

 A description of this rock is given in the above cited paper ; but 

 since this was published a chemical analysis of the type-rock has 

 been made by Mr. Alex. Scott (Table I) which fully bears out its 

 diagnosis as a new type. Mr. Scott has also executed an analysis 

 of the Barshaw lugarite (Table I), which shows a very close re- 

 semblance to the type-rock of Lugar. The quantitative mineral 

 composition of some of these rocks is shown in Table II. 



Variety 1. — This rock occurs about the middle of the Barshaw 

 exposure, overlying the bekinkinite. It is decidedly less melanocratic 

 than the latter rock, as is shown in Table II. It may be described 

 as a mesocratic facies, in which there is approximate equality between 

 the lighter and darker constituents. It is characterized by the 

 abundance of equidimensional and euhedral titanaugite, which is of 

 a highly pleocbroic variety. Outgrowths of barkevikite occur, but 

 are comparatively rare, whilst ilmenite, in process of alteration to 

 leucoxene, has increased in amount as compared with the bekinkinite. 

 The leucocratic groundmass is much altered, but large patches of 

 orthoclase may be seen, as well as areas of analcite which frequently 

 shows anomalous birefringence. The nepheline is completely altered 

 to a dusty yellowish material. Very faint ' ghosts ' of plagioclase 

 felspars occur in the turbid groundmass. 



Variety 2. — This variety forms the major portion of the schlieren 

 towards the top of the exposure. It is an even-grained mesocratic 

 rock characterized by the abundance of red euhedral barkevikite, as 

 well as the purple titanaugite, often in intergrowth. The ground- 

 mass in this rock is comparatively fresh. In it may be recognized 

 clear, fresh plagioclase, often corroded and traversed by anastomosing 

 veins of analcite. The felspar crystals are often eaten out by analcite, 

 leaving very ragged remains embedded in the latter mineral. Orthoclase 

 occurs rather abundantly, either as marginal zones to the plagioclase 

 felspars, or much altered and only recognizable in small clear patches 

 surrounded by various alteration products. Nepheline occurs in 

 broad anhedral plates with the characteristic streaky alteration, and 

 poikilitically enclosing the earlier constituents. There is some clear 

 interstitial analcite. When enclosed in nepheline the pyroxene 

 becomes a variety close to aegirine ; and the crystals of titanaugite 

 always have a narrow green marginal zone where they abut on 

 nepheline or analcite. The nepheline, and the leucocratic ground- 

 mass in general, is riddled with needles of apatite. This rock 

 differs from the preceding only in that the quantitative relations of 

 titanaugite and barkevikite are reversed (Table II). 



Variety 3. — This occurs in schlieren along with the preceding type. 

 It is a rock of a pinkish colour, and containing black prisms of 

 barkevikite. In thin section it is seen to be a leucocratic develop- 

 ment of the preceding variety. The ferromagnesian minerals have 

 dwindled in quantity and size. Titanaugite has totally disappeared, 

 and barkevikite alone is left in any quantity. On the other hand 

 there is a development of minute prisms of segirine-augite, enclosed 



1 Tyrrell, Qeol. Mag., Dec. V, Vol. IX, pp. 77-8, 1912. 



