Notices of a late Visit to the Parallel Roads of Lochaber, 33 



sion, and that simple modification of existing forces, to which 

 we have given the name elective polarity, and which seems 

 sufficiently embracing to account for all. 



It appears then to be sufficiently established, that from the 

 deportment of crystalline bodies in the magnetic field, no di- 

 rect connexion between light and magnetism can be inferred. 

 A rich possession, as regards physical discovery, seems to be 

 thus snatched away from us ; but the result will be compen- 

 satory. That a certain relation exists, with respect to the 

 path chosen by both forces through transparent bodies, must 

 be evident to any one who carefully considers the experiments 

 described in this memoir. The further examination of this 

 deeply interesting subject we refer to another occasion. 



Nature acts by general laws, to which the terms great and 

 small are unknown ; and it cannot be doubted that the modi- 

 fications of magnetic force, exhibited by bits of copperas and 

 sugar in the magnetic field, display themselves on a large 

 scale in the crust of the earth itself. A lump of stratified grit 

 exhibits elective polarity. It is magnetic, but will set its 

 planes of stratification from pole to pole, though it should be 

 twice as long in the direction at right angles to these planes. 

 A new element appears thus to enter our speculations as to 

 the position of the magnetic poles of our planet ; the influence 

 of stratification and plutonic disturbance upon the magnetic 

 and electric forces. 

 Marburg, May 1850- 



II. Notices of a late Visit to the Parallel Roads of Lochaber, 

 By James Bryce, Jun., M.A., F.G.S.* 



THE Lochaber glens have been subjected to so keen a 

 scrutiny by the advocates for the various theories of the 

 Parallel Roads, that it cannot be expected there should remain 

 many facts of importance to be yet ascertained. By this cir- 

 cumstance, however, the obligation upon an observer at once 

 to make known such facts as may have come under his notice 

 is rendered more imperative, while the value of new facts is 

 enhanced. Observations, which in other circumstances would 

 be scarcely deemed worthy of record, become of importance 

 when viewed in connexion with an inquiry such as this, which, 

 after all the discussion elicited by it, still remains the great 

 unsolved problem of Scottish geology. In submitting the fol- 

 lowing communication, it is not my purpose to advance a new 



* Communicated by the Author, and containing the substance of a paper 

 read to the Philosophical Society of Glasgow, March 6, 1850. 



Phil. Mag, S, 3, Vol, 37. No, 247. July 1850. D 



