in October, IS22. 183 



strata, under which Pompeia and Herculaneum lie buried, were 

 deposited by alluvial torrents of this nature ; and I make no 

 question, but that parallel phenomena, on a larger scale, pro- 

 duced those massive formations of tufas and breccias, which 

 shew themselves in such abundance around and upon the ex- 

 tinct colossal volcanoes of central France. 



P.S.— I open my letter to say, that accounts have just arrived from Sicily, 

 of an earthquake having done great damage in that island. Palermo has 

 been shaken dreadfully, about 'hirty lives lost, and houses injured to an 

 extent of loss equal to half a million sterling, it is said. Messina and 

 Catania have suflered much less. It is difficult to say whether this cala- 

 mity has any connexion with the eruption of Vesuvius last year, or with 

 the dreadfully stormy weather we have had since. It is a very unusual 

 phenomenon at Palermo. 



References to Plate. 



(A) Lowest lip of the crater immediately above Bosco Ire Case, and 

 facing Pompeia. In this direction the side of the cone was split open 

 during the eruption, and a large crevice formed, which threw up lava, 

 scoria;, and sand, on five or six points. 



(B) Punta del Palo, the highest peak of the actual cone, and fronting the 

 North. 



Art. II.— On Mineral Veins. By J. Mac Culloch, 

 M.D., F.R.S. Communicated by the Author. 



In a practical view, there is not a subject in the whole range 

 of geology of greater importance, than that which relates to the 

 history of mineral veins ; and, accordingly, there are few that 

 have been more examined. Neither is it by practical miners 

 alone that this subject has been investigated ; since theoretical 

 geologists have not only compared, and reasoned on, the facts 

 which these persons have brought to light, but have themselves, 

 on many occasions, undertaken the labour of personal exami- 

 nation. It is, nevertheless, true, that, excepting in a very few 

 particular cases, confined to narrow districts, which have been 

 the subjects of great experience, no general rules have been 

 established, from which any useful practical results have been 

 deduced, or whicli are capal)le of laying the foundation of a 

 rational theory respecting their formation and origin. We can 

 neither conjecture, « priori, in what districts or in what rocks 



