44 



The Cornish tin ores are said to be the most pure, as they 

 contain less iron and arsenic than those of Bohemia, Saxony, 

 &c. The crystals are mostly confused : specimens however 

 are sometimes found (and preserved to gratify the curious) 

 which are very distinct and beautiful. They resemble bottle 

 glass ; are mostly of a black hue, approaching a brownish 

 horny lustre ; sometimes brighter, and with a fiery sparkling, 

 varying to red, gray, or whitish. The crystals are the cubic 

 or octaedral modifications : the perfect cube has never, I 

 believe, been found. The octaedron, I am told, is perfect 

 in the Honourable Mr. Greville's collection. I have 

 one nearly so. They often press against each other, 

 forming macles, &c. This ore is found varying, sometimes 

 amorphous, in the quartzose, decayed granite, or growan, 

 killas, and other rocks : also in streams, and is then called 

 stream tin. It occurs also in pebbles, and sandy particles. 

 A rare species, called wood tin, or tin haematites ; also an- 

 other called tooth tin, and sulphuret of tin, are found in 

 different parts of Cornwall. There is very little tin in Devon *• 

 shire, and none in any other county of Great Britain. 



