60 



there was a reniform prominence. In many of those shells a fibrous struc- 

 ture, could be distinctly traced, — the fibres appearing to converge as in 

 globular minerals having a fibrous structure, such as wavelite, &c. 



The formation of this hydrated silicate of potash may perhaps be 

 attributed to two, or even three causes. Firstly, the carbonic acid of the 

 air was gradually absorbed and combined with the potash of the basic 

 silicate, by which gelatinous silicate was precipitated upon the lumps 

 of undissolved silicate. Secondly, the lumps, in slowly dissolving, formed 

 an almost concentrated solution of basic silicate in their neighbourhood ; 

 this solution produced a diffusive current, which slowly brought a por- 

 tion of the solution of carbonate of potash from the surface, where it had 

 continued to absorb more carbonic acid after the precipitation of the 

 gelatinous silicate ; this solution must therefore have contained some 

 bicarbonate of potash, and on coming in contact with the solution of 

 basic silicate, must have produced carbonate of potash, and a less basic 

 silicate of potash, which, if rapidly formed, would be precipitated as a 

 powder, but being very slowly formed, crystallized out in obedience to 

 any direction impressed upon the molecules by the molecular forces in 

 action in the solution and underlying mass. This change would of 

 course take place more rapidly where the solution would be densest, that 

 is, near the undissolved lumps, and hence the warty crystallizations would 

 begin there. But a third cause may also aid in producing the latter re- 

 sult. We know that a glass rod, a piece of glass, or other object pro- 

 jecting from the bottom of a vessel containing a saline solution, will 

 generally induce crystals to form upon it : a crystal of the salt in solution 

 dropped into it will still more strikingly act in the same way. It may 

 be, then, that the lumps acted as so many centres of cohesive force, 

 which acted the more rapidly the nearer they were to the surface of con- 

 tact of the pasty mass and supernatant liquor. 



MONDAY, JANUARY 13, 1862. 



The Yeet Eev. Chaeles Geaves, D.D., President, in the Chair. 



The President called the attention of the Academy to the great loss sus- 

 tained by the Academy, in common with the public at large, by the 

 lamented deaths of his Eoyal Highness the Prince Consort, Honorary 

 Member of the Academy, John O'Donovan, LL. D., and the Eev. Eobert 

 Carmichael. 



An Address to her Majesty the Queen on the occasion of the Prince 

 Consort's death was read by the President, and unanimously adopted by 

 the Academy ; and the President was requested to transmit the same for 

 presentation to her Majesty. 



Eev. Eobert G. Cather, LL. D., Percy Pitzgerald, Esq., and Henry 

 "W. "Wilkie, Esq., Avere elected members of the Academy. 



The Eev. Dr. Eeeves read the first part of a paper " On the Eound 

 Tower of Lusk." 



