O. W. Tyrrell — Bekinkinite of Barshaw, Renfrewshire. 305 



Scotland. A preliminary description of this rock as a weathered 

 theralite was given hy Mr. E. B. Bailey in 1909. ? In the previous 

 year a chemical analysis by Mr. E. G. Radley had appeared. 2 A fuller 

 description is given in the Survey Memoir on the Glasgow District 

 (19 ll). 3 According to Mr. R. G. Carruthers the theralite is probably 

 part of an igneous mass which is persistently found at the Hurlet 

 Limestone horizon of the Carboniferous Limestone Series in the 

 Paisley district. The petrography of the rock, as investigated by 

 Mr. Bailey, makes clear its relationship to the melanocratic ijolites 

 of Madagascar described by Lacroix, 4 and named ' bekinkinite ' by 

 Rosenbusch. 6 It is considered as a special modification of the Paisley 

 teschenite or dolerite. 



The unique character of the rock in British petrography is suffi- 

 ciently indicated by its identification with bekinkinite, which was 

 formerly only known from the type-locality of Bekinkina in 

 Madagascar. During recent visits to the Barshaw exposure other 

 varieties of the rock were found, principally as schlieren drawn out 

 as thin streaks in the predominant melanocratic or mesocratic 

 variety. These schlieren provide mesocratic and leucocratic facies 

 of the type, and are identical with the rock described as lugarite. 6 

 In view of the discovery of these varieties, the unique character of 

 the rock, and the fact that the old quarry at Barshaw is on a building 

 site and is being made a dump for refuse, it has been thought advisable 

 to give a full description before the exposure disappears. 



Field Relations. 

 The Barshaw bekinkinite is obtained from an old quarry situated 

 in a plantation a little to the east of Barshaw House, \\ miles east 

 of Paisley, along the Glasgow road. The opening is very shallow, 

 the greatest depth of rock seen being only 5 feet. The eastern part 

 of the quarry shows a ledge of hard rock, the base of which consists 

 of the melanocratic variety in a rather decomposed condition. Towards 

 the top of the exposure irregular patches and streaks of a light- 

 coloured pinkish rock, crowded with small black prisms and needles, 

 begin to appear. These are usually drawn out into irregular streaks 

 or schlieren, but sometimes form much-involved, irregularly-shaped 

 patches embedded in the darker type. These ' facies de variation ' 

 show considerable differences amongst themselves in texture and the 

 relative proportions of the black prismatic minerals (barkevikite and 

 titanaugite), but the general contrast of the pale leucocratic schlieren 

 with the predominant dark, basic, melanocratic type remains the 

 most striking feature of the exposure. In all, including the melano- 

 cratic facies and the light- coloured schlieren (lugarite), no fewer than 

 seven distinct varieties of rock may be distinguished by microscopic 

 examination (see Petrography, postea). The leucocratic schlieren 

 seem to be more abundant towards the top of the exposure, but the 



1 Summary of Progress of Geological Survey for 1908, 1909, p. 44. 



2 Summary of Progress of Geological Survey for 1907, 1908, p. 55. 



3 Geology of the Glasgow District (Mem. Geol. Surv.), 1911, pp. 116, 134. 



4 Nouv. Arch. Mus. (4), i, p. 135, 1902 ; ii, p. 227, 1903. 



5 Micr. Phys., ii, p. 441, 1907. 



6 Tyrrell, Geol. Mag., Dec. V, Vol. IX, pp. 77-8, 1912. 



DECADE VI. — VOL. II. — NO. VII. 20 



