ITALY. L E T T E R V., 57 



fay that all agates, jafpers, horn-flints, and finer 

 precious ftones, have been prepared by volcanic 



fire, 



tank matrices ; that is to fay, but mediate productions of the 

 fire, as being vilibly produced by water, either foaking through 

 and into the holes of volcanic ftones, and depofiting therein 

 the flint-like fire-ftriking fediment of chalcedony ; or, if pro- 

 perly qualified and heated by natural fire or fermentation, preci- 

 pitating the fame under other circumftances. The former ap- 

 pears to convi6tfon> by the Vicentine and Iceland-chalcedonies j 

 the latter by a fingular phenomenon, which I fhall take no- 

 tice of. 



The Vicentine chalcedonies, found in volcanic-tufo, contain 

 now and then inclofed in their middle drops of the water 

 which produced them; and the Iceland-chalcedonies bear 

 likewife undoubted marks of an aqueous origin. The Tranfla- 

 tor knows, by good authority, that they have been difcovered 

 but of late ; and ocular infpeclion has convinced him, not only 

 that thefe Iceland-chalcedonies are equal in grain and colour to 

 the Oriental ones, but remarkably fuperior to them on account 

 of their bignefs. He had large pieces fent from Copenhagen 

 above a foot fquare : and what is more to the fubjecl, inclofed 

 in a brownifh tufo, in which they appeared to have been Gra- 

 tified or fucceffively depofited by water; confifHng more or 

 lefs of white or tranfparent beds, about an inch thick, and 

 flicking as clofe together as the fimilar ftrata of the coloured 

 agathes or onyx. Mr. Bank's late voyage to Iceland brings us 

 flill a irep further. He examined there the marvellous inter- 

 mittent fpouting hot wells, called the Gey/tr's, at Laugafell^ 

 which in the middle of a folfatara or ancient volcano, by their 

 accumulated fediments have produced or raifed a wide floping 

 hill of white hies or fot-Jlcne. I forbear to draw from this 

 fingular phenomenon the many con fequences. which it offers 

 for Natural Hiftory j obferving only, what is more to the pur- 



