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the fea, and thus enable myfelf to perceive 

 fubaqueous bodies at a certain depth as cir- 

 cumrtances might require. By thefe means 

 I difcovered that the prifms were immerfed 

 in the fea to the depth of fome feet. The 

 breadth of fome of the prifms was a foot and 

 a half, but that of others lefs. 



This prifmatic lava merits to be very ac- 

 curately defcribed, fmce, in profecuting my 

 voyage along the fhore of Felicuda, I met 

 with it in feveral other places, and fhall 

 again have occafion to mention it. Its bafe 

 is a horn-ftone of the black colour of iron, 

 and fo compact that the fmalleft bubble is 

 not perceivable in it; it muft, therefore, be 

 claffed among the heavy lavas. The edges 

 of the thinned flakes of it are tranfparent, 

 and give fparks with fteel. Its fragments 

 are amorphous, and receive a polilh, but 

 without luftre. It attrads the masfnetic 



o 



needle at about the diftance of three lines. 



The powder of this lava is cinerltious, and 



impalpable, and attaches to the finger. In 



VQL, III. H it 



