330 Reports & Proceedings — Mineralogical Society. 



A series of crystalline rocks, for which it is proposed to use the 

 name Turoka Series, is situated just below the great lava plateau of 

 the Kapiti Plains, and forms the ground drained by the head-waters 

 of the Turoka River. The following rock-types are present in the 

 chief section, in the following apparent upward succession : — 



(1) Hornblende-schist, seen to a thickness of 3ft. Sin. ; (2) flaggy 

 and impure mai'ble, 3 feet ; (3) biotite-gneiss, 2 feet ; (4) calc-mica rock 

 with lenticles of biotite-gneiss, 3 ft. 8 in. ; (-5) hornblende-schist similar 

 to No. 1, 1 foot; (6) impure calc-rock, 2 feet; (7) quartz-felspar vein, 

 2 feet ; (8) hornblende-schist, 2 feet ; and (9) impure calc-rock, resembling 

 No. 5 and about 4 feet thick. 

 A. detailed petrographical description is given of the various rock- 

 types present in the series, which, in addition to those mentioned 

 above, includes kyauite-garnet-gneisses and a scapolite-garnet rock. 



The author concludes that the group represents a series of 

 metamorphosed arenaceous and calcareous sediments, and that there 

 is a complete passage from calc-mica rocks into biotite-gneisses. 



Mineralogical Society. 



June 17.— Dr. A. E. H. Tutton, F.R.S., President, in the Chair. 



W. L. Bragg : Crystal Structure as revealed by Rontgen Radiation. 

 An analysis of the ditfraction patterns obtained when X-rays traverse 

 a section of a crystal shows that in many simple crystals the diifraction 

 is caused by a set of points arranged on a space-lattice. This is the 

 case when the molecule contains either a single heavy atom of at 

 least twice the atomic weight of the other constituents, or only two 

 atoms of nearly the same atomic weight. By comparison of the 

 pattern given by certain alkaline halides, such as K C I and K Br, 

 a definite structure of these cubic crystals is clearly indicated, and it 

 would appear that the atoms are arranged on a space-lattice whose 

 elementary parallelepiped is a cube, alternate atoms being along the 

 axes, so that atoms of one kind form a face-centred cubic space- 

 lattice. These conclusions are confirmed by a comparison of the 

 distances between planes parallel to the various faces of these crystals 

 carried out by means of the X-ray reflection-spectrometer, and, it 

 appears that a single atom is associated with each point of the space- 

 lattice which diffracts in the case, for instance, of the alkaline halides, 

 calcite, fluor, blende, and pyrites. If the suggested structure of the 

 crystals is correct, a simple calculation gives the absolute wave- 

 length in centimetres of the homogeneous components in the X-ray 

 beam from a platinum anticathode. — H. V. EUesworth : The Crystal 

 Habit of Topaz from New Brunswick, Canada. , Topaz, a rare 

 mineral in Canada, occurs in York Co., New Brunswicli, associated 

 with wolframite, molybdenite, and a little fluor. On the crystals the 

 forms 110, 120, Oil, 112 are prominent, but other pyramid and 

 prism forms are sometimes present, sixteen forms altogether being 

 observed. Dull faces were coated with silver by Brashear's process, 

 in which an ammoniacal solution of silver nitrate is reduced by 

 a sugar solution. — Dr. G. T. Prior: On the Meteoric Stone which 

 fell at Baroti, Punjab, India, in September, 1911. The stone, 



