348 B. Hohson — An Iruh AiicjUite. 



also ratliei' acute zig-zag contortions. Under the microscope the structures charac- 

 teristic of mechanical metamorphism show more decidedly. The clear granular 

 patches of quartz, etc., have the well-known form of lenticular streaks, and smaller 

 patches of similar character occur like ' eyes ' imbedded in inconstant bands com- 

 posed largely of colourless mica, the micaceous films showing the usual wavy 

 parallel arrangement and clinging round the enclosed ' eyes.' In some broader 

 bands, also rich in mica, both colourless and yellow or brown, the structures, 

 developed by a shearing movement of the mass, are seen in various stages. First 

 a system of minute uusymmetrical parallel folds is produced, their axial planes 

 inclined at an angle of about 45" to the general schistosity of the rock. These folds 

 become compressed and pushed over until they pass into little reversed faults about 

 •oiVo iuch apart. The faults are formed at an angle of about 30° with the general 

 direction of schistosity, but by further movement they come to coincide more closely 

 with that direction, and are finally lost in the parallelism of the micaceous streaks. 



The clear granular patches in the slide consist, at least for the most part, of quartz. 

 The intricate interlocking of the several grains proves that the whole has crystallized 

 in situ, and their imperfect extinction or 'spectral polarization' indicates a condition 

 of internal strain. The rock may have been originally a shale or slate with some 

 gritty bands. It compares very closely with the Skiddaw Slates, where they have under- 

 gone locally profound dynamic metamorphism, as at Brownber, in Westmoreland.^ 



(8) C^. Sov.th of Start Farm.'' 



This is a t)rpe of rock which corresponds to what has sometimes been called a 

 quartz-schist. The schistose character is but slightly marked in the hand-specimen. 

 Minute scales of mica are arranged to give a parallel structure ; but the mineral is 

 onlv sparingly present. 



Under the microscope the rock is seen to consist almost exclusively of clear grains 

 of quartz of varying size and generally irregular shape. It is not clear that there 

 has been any considerable recrystallization, and there is certainly nothing like the 

 degree of metamorphism evidenced by specimen B.,. The few scattered flakes of 

 colourless mica may be original. The slice is traversed by numerous little cracks 

 cemented by opaque iron-ores. These are wavy and branching, but maintain a 

 rough parallelism throughout the slice, agreeing in direction with the scales of mica. 



III. — An Irish Augitite. 



By Bernard Hobson, M.Sc, F.G.S. ; 

 Assistant Lecturer in Geology at the Owens College, Manchester. 



WHEN writing my paper " On the Igneous Rocks of the South 

 of the Isle of Man," ^ I was led to comjiare a Manx melaphyre, 

 from Scarlet Point, with a rock described by Prof. E. Hull ^ as a 

 melaphyre, occurring at Ballytrasna, near Limerick, and belonging 

 to the " Upper Ti'ap-band," a little below the basal shales of the 

 Coal-measures. Through the kindness of Prof. Hull, a chip of the 

 rock was sent to me b}' the Irish Greological Survey. The specimen 

 was black and basaltic-looking. I did not obtain satisfactory sections 

 of it in time for my paper, but have since had excellent ones made. 

 On examining them I was immediately struck by the resemblance 

 of the rock to the augitite of Paschkapole,' between Velmin and 



1 See paper by Prof. Nicholson and Mr. Marr, with Appendix ; Quart. Journ. 

 Geol. Soc. vol. xlvii. pp. 612-514 (1891). - Plate 71, tig. 



3 Quart. Journ. Geol. Soc. vol. xlvii. (1891), pp. 432-450 (reprinted with additions 

 in Yn Lioar Manninagh, 1892, pp. 337-348). 



■• "On the Microscopic Structure of the Limerick Carboniferous Trap Rocks," 

 Geol. Mag. 1873 (pp. 153-161), p. 157. Prof. Hull gives a list of papers relating 

 to the geology of these rocks. 



5 Mentioned by H. Eosenbusch, Mikroskopische Physiographic der Massigen 

 Gesteine (1887), p. 821. 



