I 23 ] 



the globe, and afFord not the flighteft indication of their origin ^ 

 whins, though they abound in Scotland and fome other countries, 

 are in comparifon of the former but thinly fcattered over the 

 furface of the globe. Some refemblance betwixt them and lavas 

 has been long noticed. I fhall now briefly mention a few of 

 the difcriminating charaders of the artificial and natural whins, 

 which may in moft cafes prevent us from confounding them, 

 or afcribing to them a common origin. 



I ° The natural whins, particularly amygdaloids (vulgarly called 

 toadftones) frequently contain calcareous fpar and zeolyte ; now 

 as the former contains fixed air, and the latter a notable pro- 

 portion of water, I hardly think Sir James, who profefTes not 

 to agree with Dr. Hutton in all points, will allow thefe to 

 have been vitrified or fufed. 



2^ The natural whins, according to Dr. Kennedy's ftatement, 

 lofe five per cent, of water and other volatile matter when 

 heated to rednefs. It is not faid whether the artificial lofe any 

 part of their weight by fuch treatment, but it is plain they 

 would not, fince even the lavas of Catania and Piedemonte, 

 though of ancient date, loft none, as Dr. Kennedy exprefsly 

 notices, and has thus afforded an excellent criterion for diftin- 

 guifhing the long contefied origination of thefe fubftances. 



.3« A. 



