Obituary Notice of the late Br M'Bain. 255 



central band showing a prismatic structure, the prisms being directed inwards 

 from the outer walls of the vitreous zone. (This and the three following 

 figures have been drawn from his own observations by Mr B, N. Peach. ) 



Fig. 2. View of a square yard of the outer wall of the vitreous central 

 band, showing the polygonal arrangement of the prisms and their investing 

 sheaths or ribs. 



Fig. 3. View of a smaller portion of the same wall to show the detailed 

 structure of the ribs {a, a) and their vitreous cores (&, b). 



Fig. 4. Profile of a part of the weathered face of the wall, showing the 

 way in which the hard ribs or sheaths project at the surface. 



Fig. 5. Microscopic structure of the vitreous core. This section shows a 

 crystal of augite, enclosing magnetite and surrounded with microliths, each 

 of which consists of a central rod of pale yellow glass crusted with pale yellow 

 isotropic globulites. The glass around this aggregation is clear, but at a 

 little distance globulites (many of them elongated and dichotomous) abound, 

 with here and there scattered microliths, some of which are curved and spiral. 

 (800 diameters. ) 



Plate VI. — Microscopic Sections of Eskdale Dyke. 



Fig. 1. Portion of the outer or chilled edge of the outer dolerite band 

 (6 of fig. 1 in PI. v.), Shaw Burn. (70 diameters.) 



Fig. 2. From the more coarsely crystalline central part of the same 

 marginal dolerite. (70 diameters.) 



Fig. 3. Structure of the hard rib or sheath surrounding the vitreous core 

 (a, a, in fig. 3 of PL V.), Shaw Burn. (70 diameters.) 



Fig. 4. Structure of the vitreous core {b, b, in fig. 3 of PI. V.), Shaw 

 Burn. The colourless crystals are the felspars, the greenish are augite, the 

 black are magnetite. The pale brown glass with its beautiful fluxion strac- 

 ture and crowded microliths forms the largest part of the rock. 



Fig. 5. Structure of the vitreous central band, Wat Carrick. This 

 section shows with a magnifying power of 250 diameters the fluxion structure 

 of the glass, the aggregation of the globulites and darkening of the glass 

 against the felspars, and the bleached unindividualised character of the glass 

 round the augite and magnetite. The augites are seen to bristle with micro- 

 liths usually straight and loaded with investing globulites. (See fig. 5, PI. V. ) 



Fig. 6. From centre of vitreous part of dyke, Kirkburn above Langholm. 

 The base is here crowded with pale yellow and greenish globulites and 

 curved fibre-like microliths. (250 diameters. ) 



VI. Obituary Notice of the late Br Jctmes M'Bain. 

 By David Grieve, Esq., F.G.S. 



(Kead 17th December 1879.) 



Dr M'Bain, on his deathbed, gave me some particulars of 

 his early career, which with some additional matter I 

 propose to read to the Society. 



