572 Reports and Proceedings — Mineralogiccd Society. 



general glassy and cryptocrystalline nature, which he does not regard 

 as a result of chilling, but suspects is dependent upon the viscosity 

 of the basic magma. 



He brings forward evidence to prove that the position occupied 

 by the tachylyte is independent of tectonic features, but follows 

 directly from solution and corrosion of the granitic rocks by the 

 basic magma. 



III. MiNEEALOGICAL SoCIETY. 



Anniversary Meeting, November 10. — Dr. A. E. H. Tutton, F.E.S., 

 President, in the Chair. 



Professor W. J. Lewis : Albite ; its Crystal Elements, etc. New 

 values of the elements were obtained based upon measurements made 

 on well-developed twinned crystals from Alp Rischuna. Chemical 

 analysis showed them to be very pure albite. — H. Collingridge : The 

 Determination of the Maximum Extinction Angle, Optic A.xial Angle, 

 and Birefringence of Monoclinic Pyroxenes in Thin Sections. The 

 method depends on the presence of well-defined twins about 100, and 

 the visibility of an optic axis through one individual. From observa- 

 tions in this individual of the positions of the trace of the optic axial 

 plane and the twin plane, the extinction angle, and the position of 

 the visible optic axis, and in the other the extinction angle and the 

 birefringence, and, if possible, the positions of an optic axis and 

 the trace of the optic axial plane, the requisite determinations may be 

 made. — Professor H. L. Bowman : Note on Calcite from the Chalk at 

 Corfe Castle, Dorset. Good crystals, which occur in veins in the 

 Upper Chalk, are of the pointed habit, the forms being / (111) and 

 X (212). Interpenetrant rhombohedra twinned about the c axis as 

 in cinnabar are not uncommon. — A. Scott : Barkevikite from Lugar, 

 Ayrshire, and Litharge from Persia. The former occurs in lugarite in 

 prismatic crystals up to 75 mm. in length with mean refractivity 

 1'690 and very intense pleochroism, c very dark brown, b reddish- 

 brown, a light yellow ; in chemical composition it is fairly close to 

 the type mineral from Barkevik. The latter was found at Larshuran, 

 Persia, as a red mica-like crystalline mass ; it is biaxial with mean 

 refractivity 1"735, the double refraction being very weak, and contains 

 over 97 per cent of lead oxide, the remainder being copper oxide 

 with a little antimony oxide. — Dr. G. T. Prior : The Meteorites of 

 Uwet, Kota Kota, and Angela ; the identity of Angela and La Primi- 

 tiva. The meteoric iron of Uwet, Southern Nigeria, said by natives 

 to have fallen about ninety years ago, is a hexahedrite of the Braunau 

 type, containing about 6 per cent of nickel. The meteoric stone of 

 Kota Kota, Marimba District, British Central Africa, said by natives 

 to have been seen to fall some years ago, is a chondrite, probably 

 belonging to the crystalline spherulitic group. The meteoritic iron 

 of Angela, near Iquique, Chili, was found in the nitrate beds. It is 

 an ataxite, containing about 4*5 per cent of nickel and enclosing large 

 nodules of schreibersite, and is probably identical with La Primitiva. 



The following Officers and Members of Council were elected : 

 President, Dr. A. E. H. Tutton, F.R.S. ; Vice-Presidents, Professor 



