Reports d:. Proceedings — Edinburgh Geological Society. 521 



of the Australian Slate Quarry, Willunga, which works a belt of 

 slate of late pre-Cambrian or Lower Cambrian age, apparently of 

 very good quality. 



Polarized Light in the Study op Ores and Metals. By F. E. 



Wright. Proc. Amer. Phil. Soc, vol. Iviii, 1919, pp. 410-47. 

 Examination of Ores and Metals in Polarized Light. By F. E. 



Wright. Mining and Metallurgy, No. 15.8, 1920. 



rPHE first of these papers gives an elaborate mathematical analysis 

 -^ of the theory of reflection of polarized light from polished 

 surfaces of opaque substances, together with a description of various 

 forms of optical apparatus adapted to determine the isotropic or 

 anisotropic character of such substances ; in certain cases the 

 strength of the double refraction can be determined approximately. 

 Methods involving the use of a bi-quartz-wedge-plate are the 

 simplest, and have given the best results. In general, refractive 

 indices cannot be ascertained on small polished random sections. 

 The second paper contains a similar account of the practical appli- 

 cation of these methods, with descriptions of the apparatus used by 

 the author in his investigations. 



REPORTS AND PROCEEDINGS. 



Edinburgh Geological society. 



March 17, 1920.— Mr. E. B. Bailey, M.C., B.A., F.R.S.E., F.G.S., 

 President, in the chair. 



1. "Notes on the Glacial and Post-Glacial Geology of the Dee 

 Valley, from Balmoral to Aboyne." By Dr. Alex. Bremner, 

 Aberdeen. 



A glaciation map of the district was exhibited. In all 220 hitherto 

 unrecorded strise had been noted. There was no marked difference 

 in direction between strise due to the Ice Sheet and those due to the 

 Valley Glacier. Lateral moraines and the terraces usually called 

 " fiuvio-glacial " were discussed. Of the latter there were many 

 fine and hitherto unmapped examples. The effects of marginal 

 drainage were very we.l exemj)]ified in the district, and it was 

 suggested that the truncation of spurs might be due in great measure 

 to the cutting of marginal channels during the advance of glacier 

 or ice sheet. Maps showing the river terraces were exhibited, and 

 discrepancies between these and the Geological Survey maps pointed 

 out. It was shown that there was no evidence for the former 

 existence of a lake below Ballater. 



2. " River Terraces." By Dr. Alex. Bremner, Aberdeen. 



The contributions of Hugh Miller, jun., and Professor W. M. 

 Davis to the theory of river terracing were reviewed. The former, 

 who gave an adequate explanation of amphitheatre terraces (i.e. 

 terraces having a front, on the whole, convex towards the river), 



