VOL. XLVI.]^ PHILOSOPHICAL TKANSACTIONS. 101 



The 3d communication on this interesting subject is from Mr. Watson, who 

 says, that this platina di Pinto is likewise called in America, Juan Blanco. It is 

 not mentioned in any author he has met with, except Don Antonio d'Ulloa, who, 

 in the History of his Voyage to South America, vol. ii. b. 6, ch. 10, which he 

 has here extracted, and translated from the Spanish, when giving an account of 

 the gold and silver mines in the province of Quito, and of the various methods 

 of separating these metals from other substances, with which they are combined, 



says, that " in the territory of Choco there are gold mines, in which that 



metal is so disguised and enveloped with other mineral substances, juices, and 

 stones, that, for their separation from the gold, they are obliged to use quick- 

 silver. Sometimes they find mineral substances, which, from their being mixed 

 with platina, they chuse to neglect. This platina is a stone (piedra) of such re- 

 sistance, that it is not easily broken by a blow on an anvil. It is not subdued by 

 calcination; and it is very difficult to extract the metal it contains even with much 

 labour and expence." 



In the before-mentioned work, ch. 11, the same author, when speaking of 

 the remaining works of the Indians of old, says, " the specula wrought out of 

 stones, which are found in the places of worship of the Indians, are of 2 kinds, 

 in regard to the matter of which they are made : one of these is called piedra de 

 Inga, the other piedra de Gallinazo. The first of these is smooth, of a leaden 

 colour, and not transparent ; they are usually found wrought of a circular figure: 

 one of the surfaces is plain, and as smooth as though it were made of a kind of 

 crystal ; the other surface is oval, or rather somewhat spherical, and not so much 

 burnished as the plain one. Though they vary in their size, they are commonly 

 from 3 to 4 inches in diameter; but he has seen one that was a foot and a half 

 in diameter. Its principal surface was concave, and. much augmented the size 

 of objects, for its polish was in as great perfection as though it had been worked 

 by a dextrous artist in these times." 



" This stone has certain veins, or hair-like appearances, on its surface ; by 

 which it is rendered less fit for a speculum, and is apt to break in these veins in 

 receiving any blow. Many are persuaded, or at least suspect, that the matter of 

 these is a cast composition ; and though there are some appearances of this being 

 so, they are not sufficiently convincing. In this country there are gullies (que- 

 bradas) where the mineral of them is found rough, and from whence some are 

 always taken ; but these are not now wrought for those purposes f<jr which here- 

 tofore they were employed by the Indians : but this is no reason but that some 

 of them may have been cast, as with the same material taken out of the mine, 

 they may have been made artificially, and thereby have received a greater degree 

 of perfection, as well in their quality as in their figure." He says further, " that 

 though at present these, as well as several other things found there ; are but of 



