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*' drangular, and fometimes trapezoidal pU 

 " lafters, which have been employed in 

 " buildings. Similar fiflures are likewife 

 *' obferved in tufas, and earths of different 

 " kinds, and can never miflead any perfon 

 " accuftomed to them, and acquainted with 

 •' their true caufes." 



By this faithful relation of fads, I flatter 

 myfelf, I have clearly fhown that it cannot 

 be fupported as a general hypothefis, that 

 flowing lavas take a prifmatical configura-^ 

 tion from the fudden coagulation they fuffer 

 on falling into the fea. 



It may, perhaps, be objected, that thefe 

 prifms once exifted in the lavas I obferved, 

 but that the irrefiftible violence of the 

 waves, in a long feries of years, has cor- 

 roded and deftroyed them. 



Every perfon acquainted with the fub- 

 jed: muit immediately perceive how little 

 folidity there is in this objedion. I admit 

 that the violence of the fea may, in fome 



lavas. 



