﻿480 Geological Society : — 



Since sending the above to press, I have subjected plates coated 

 with " sensitized " collodion to the action of the magnetic field. 

 I had hopes of thus obtaining a physical impress on the plate 

 which would appear on flowing the " developer." Sensitized 

 films on glass and on iron plates were placed over and between 

 the poles of an electromagnet with cores 1*7 inch in diameter. 

 Some plates were developed after removal from the magnet, 

 others while under the magnetic action (with and without the 

 light having acted upon them) ; but no trace of effect has been 

 detected. 



I had also imagined that the magnet's action should have 

 placed the affinities in a more unstable condition, so that the film 

 would rise in sensitiveness after exposure in the magnetic field; 

 but this also I could not detect ; nevertheless I have not given 

 up the supposition that some action will be evolved when more 

 appropriate films, far higher magnetic action, and more delicate 

 measures of actinic effect are used. 



February 13, 1871. 



LXI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 321.] 



December 7, 1870. — Joseph Prestwich, Esq., F.R.S., President, 



in the Chair. 



rPHE following communications were read : — 



■*- 1. " On Fossils from Cradock and elsewhere in South Africa." 



By Dr. George Grey. 



From the Karoo-beds, Dicynodont fossils and the jaw of a Rep- 

 tile, Estherice, and some coal and coal-plants (Lepidodendron, Sigil- 

 laria &c.) were the chief specimens noticed by the author. Some 

 Stigmarice from the Old Coal of Low T er Albany, and gravel and mis- 

 cellaneous minerals from the Diamond Fields, formed part of the 

 collection. 



2. " On some points in South- African Geology." — Part II. By 

 G. W. Stow, Esq. 



This paper commenced with a detailed account of the Forest 

 zones, coal, and other strata of the Karoo formation, as seen in 

 sections in the Winterberg and Stormberg. The author particularly 

 pointed out the position of the Fern-beds at Dordrecht, of the Rep- 

 tilian remains found on the Upper Zwartkei, and of the Coal on the 

 Klaas Smits River. He next referred to the climatal changes of 

 South Africa, as indicated by its geology and fossils, particularly the 

 Karoo-beds, the Enon conglomerate, the Trigonia-beds, the several 

 Posttertiary shell-beds, and especially the present surface conditions, 

 which he regarded as due to ice-action, as evidence of which he 



