( i7« ) 



ginadon of the narrator; yet they common- 

 ly v*^ant one eflential requlfite ; that is, li- 

 thological deicriptions of the bodies ejeded 

 by thefe burning mountains. As glafs and 

 pumices, however, are known even to thofe 

 who are unacquainted with this part of na- 

 tural fciencc, we may, with certainty, or, at 

 leaft, with the ftrongell probabihty, con- 

 elude, that they are produced by the volca- 

 nos in the defcriptions of which we find 

 them exprefsly mentioned as making a part 

 of the ejedled matters, and that they are not 

 produced when not mentioned. Thus in 

 Iceland, the greater part of which ifland is 

 only an accumulation of volcanos either ex- 

 tindt or adive, it is certain, from the ac- 

 counts of travellers, that numerous glafTes 

 ace found, to which the name of Icelandic 

 agate has improperly been given, only be- 

 caufe they have the luftre and beauty of 

 that ftone. The prefent eruptions of this 

 ifland, likewife, not unfrequently contain 

 pumices ; but no perfon has ever afTerted 

 that there are entire mountains of thefe 

 ftones, or of glafles. 



S The 



