1813.] Geological Society. 153 



set free. When the experiments were made in glass retorts, the 

 glass was corroded, and silica ted fluoric acid gas obtained. When 

 they were made in plalinum vessels, the metal was corroded, and 

 a red or brown powder formed. It would seem from the trials 

 made that fluorine has so violent an action on all other bodies 

 that it is very difficult, if not impossible, to obtain it in a sepa- 

 rate state. The author promises to continue this subject in a 

 subsequent paper. 



5. A paper by Mr. Alman on the method of freeing equations 

 from surds, though the roots be pretty high in their dimensions. 

 From the nature of this paper it could not be read at full length, 

 so that it is not possible to give any idea of the method em- 

 ployed by the author ; but he referred to a method previously 

 given in the Irish Transactions by Mr. Money, which he con- 

 siders as general, and which probably constitutes the foundation 

 of his own. 



The Society adjourned till the 4th of November next. 



GKOLOGICAL SOCIETY. 



On the 2d of April part ef a paper by Mr. John Farey, sen. 

 on the Ashover denundation in the county of Derby was read. 

 This part of the paper is not susceptible of abridgment. 



On the 23d of April a notice by the Rev. J. J. Conybeare, 

 relative to the slate of Tintagel, in Cornwall, was read. This 

 slate would appear to be transition slate. It answers well for 

 roofing slate, and is traversed by veins containing quartz, calca- 

 reous spar, chlorite, and adularia. 



Mr. Farcy's paper on the Ashover denudation was concluded. 

 Tfie structure of Derbyshire, according to Mr. Farey, consists 

 of alternate formations of lime-stone and toad-stone, in the fol- 

 lowing order, beginning with the lowest : — 



Lime-stone, 



Toad-stone, 



Lime-stone, 



Toad-stone, 



Lime-stone, 



Toad-stone, 



Lime-stone, 



Lime-stone shale, 



Mill-stone grit, 



Coal. 



On the 7 ill of May part of a paper, by Dr. Macculloch, on 

 the geology of certain parts of Scotland, was read. The prin- 

 cipal and Fundamental rock of the island of Jura is a rock called 

 by some granular quartz, by others granite, and by all considered 

 as a primitive rock ; but Dr. Macculloch considers it as a mecha- 

 nical deposite of quart/ and felspar, formed from the older 



