( 114 ) 



in feareh of this fubftance, brought me more 

 of it than was neceffary, which they cot- 

 leded in the fields where they worked. As 

 I was not, however, perfedtly fatished with 

 this firft obfervation, I dired:ed them to dig 

 a deep trench in one of the fields which 

 mod abounded in fpecimens of this fub- 

 ftance, with a view to try if I could dif- 

 cover a vein, thefe being only detached 

 pieces. The trench they dug was eight feet 

 deep, and five in breadth. For the depth of 

 two feet I found only a tufaceous earth, 

 containing fome of thefe vitreous pieces. 

 At a greater depth the virgin tufa- appeared,, 

 untouched by the ploughfhare, or any ruftic 

 infirument. This tufa likewife furniflied a 

 fimilar glafs, but always in detached pieces^ 

 nor was any difference perceivable in the 

 nature of thefe products, on continuing the 

 refearch to the bottom of the trench, where 

 the tufa was ftill found* 



It appears, therefore, that the glafs in tlie 

 ploughed fields had its feat in the tufa ; 

 though it cannot be affirmed with certainty, 



that 



