Geological Society. 225 



improvised. Nevertheless the agreement, such as it is, shows 

 that it will be worth while to carry out a series of experiments 



Fig. 3. 



12 amperei. 



with the accuracy and care that are needed in physical inves- 

 tigations. This I intend to do as soon as I am able. It will 

 then perhaps be possible to tell whether this method of 

 determining conductivity or field-intensity is to be relied 

 upon : it certainly in convenience and simplicity compares 

 very favourably with any of the usual methods. 



XXX. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 



[Continued from p. 159.] 



April 2, 1884.— Prof. T. G. Bonney, D.Sc., P.R.S., President, 

 in the Chair. 



THE following communications were read : — 

 1. «< The Rocks of Guernsey." By the Rev. E. Hill, M.A., P.G.S. 

 With an Appendix on the Microscopic Structure of some of the 

 Rocks, by Prof. T. G. Bonney, D.Sc, F.R.S., Pres.G.S. 



The southern part of the island is a high plateau consisting en- 

 tirely of gneiss. This is very coarse, and the bedding is seldom well 

 marked. The bedding, when visible, coincides with the foliation, 

 and the author hopes that hereafter an order of succession may be 

 established. At Rocquaine Castle occur a few slaty beds intercalated 

 in the gneiss, the origin of which is somewhat difficult to under- 

 stand. The northern part, low ground with hummocks, consists 

 principally of a group of crystalline or subcrystalline rocks, in 

 constitution diorites or syenites. They are described by Ansted as 

 sedimentary rocks metamorpbosed into syenites; but they show no 

 bedding either in the many quarries, or, in general, in the shore out- 

 crops, nor do their varieties occur in any manner indicating an order 



Phil Mag. S. 5. Yol. 18. No. 112. Sept. 1884. Q 



