[ 305 ] 



On no fubjed have philofophers been lefs cautious of the 

 delufions of imagination than on this of volcanos : the ailonifh- 

 ment excited by their awful phoenomena feems to have afFedted 

 even the underftanding of fome of their fpedators. The author of 

 many celebrated treatifes on volcanos, lately travelling into Scot- 

 land, exclaimed, at the fight of every black ftone he met wih, 

 that it was lava^ as I was informed by one of his companions*; 

 even the very excellent Sir William Hamilton has frequently been 

 feduced from the fimple path of obfervation to which notwithfland- 

 ing he profeffed to adhere, into the mazes and errors of a bafekfs 

 fyftcra|. In a letter to Sir John Pringle, May 1776, he tells us that 

 " Wherever bafaltic pillars like thofe of the Giant's Caufeway in 

 " Ireland are found there without doubt a volcano muft have ex- 

 " ifted, for they are mere lava." At pretent however I believe none 

 will pretend that the A^olcanic origin of thefe pillars is out of the 

 reach of doubt. He tells us that Vefuvius and iEtna were formed 

 by a ferics of volcanic eruptions Xi though there is no certain proof 

 that the former wits fo formed, and it is demonftrable that the latter 

 exifted as a mountain before it became a volcano. Padre Torre, who 

 has given a good defcription of Vefuvius, infifts that its primitive 

 ftamina, if I may fo call them, are not volcanic, but that it fhould 

 rather be confidered as an extenfion of the Appenines ; the number 



0,q of 



* Mr. Macie, a gentleman of the moft exa<^ and extenfive mineralogical knowledge^ 

 f Ouvres de Hamilton, p. lo. 

 % Ouvres de Hamilton, p. 11. 



