136 Reports & Proceedings — Geological Society of London. 



co-ordination. The symmetry of the new spatial forcaulse is in many 

 cases identical with the symmetry, and, in particular, sodium nitrate 

 can best be regarded as a racemate due to a mutual interpenetration 

 of optical antipodes having spatial configurations similar to those 

 suggested for the active forms of sodium chlorate, the symmetry of 

 the double molecule being identical with that of a rhombohedron. 

 The same type of molecular structure presumably exists in calcite 

 and the rhombohedral form of sodium chlorate which crystallizes at 

 high temperatures. It is concluded that many cases of dimorphism 

 are of an analogous character, and, more generally, that polymorphous 

 change is preceded by a re-arrangement of the atoms within the 

 molecule. — H. Collingridge : !Note on the Determination of the Optic 

 Axial Angle of Crystals in Thin-section. In the case where one optic 

 axis is visible in the field of view, the position of the second axis may 

 be determined more conveniently than in the Becke and Wright 

 methods from the optic axial plane and the extinction direction 

 through the centre of the field. — Dr. G. F. H. Smith : Graphical 

 Determinations of Angles and Indices in Zones. Two methods were 

 described, which, unlike the moriogram, are not restricted to right- 

 angled zones. In one a double tangent scale is placed on a pencil of 

 lines spaced as in a gnomonic projection on a zonal plane in such 

 a way that the 01 and 11 lines cross the scale at the given angles; 

 the angles corresponding to any indices, or vice versa, are read oft' 

 directly within the limits of the scale. In the second method 

 a double diagram is employed, of which one half is a new form 

 of the moriogram and the other is a representation of angles whose 

 cotangent is the difference of the cotangents of the given angles ; the 

 method is general and unrestricted in its application. — Dr. J. Drugman : 

 On the Goldschmidt Apparatus for Cutting Models of Crystals. The 

 mechanism was described, and the method of using it explained. — 

 Professor H. L. Bowman : On a Nodule of Iron Pyrites. The 

 octahedral shape and the striations on the faces truncating the coigns 

 of the tiny crystals point to their being pyrites, and not marcasite as 

 usually stated. — A Chinese bowl carved out of an amethyst geode, 

 and a set of scales and weights used by the native jewellers in 

 India for weighing pearls, were exhibited by F. jS". A. Fleischmann 

 and E. Hopkins i-espectively. 



II. — Geological Society of London. 



January 22, 1913. — Dr. Aubrev Strahan, F.R.S., President, in the 



Chair. 



The following communications were read : — 



1. "The Fossil Flora of the Cleveland District of Yorkshire. 

 I. The Flora of the Marske Quarry." By H. Hamshaw Thomas, 

 M.A., F.G.S. With Notes on the Stratigraphy by the Rev. George 

 John Lane, F.G.S. 



In this paper the author describes several plants collected by the 

 Rev. G. J. Lane and Mr. T. W. Saunders in tlie Cleveland district of 



