Il02 * PHILOSOPHICAL TRANSACTIONS. [aNNO J776. 



ridge of mountains tiiat makes the natural limit between Europe and Asia, and 

 to the east of" which the largest share of true remains of elephants, rhinoceroses, 

 and large buffaloes, is found in the banks of all the larger rivers that run from 

 the above-mentioned chain of mountains to the Northern Ocean, and yield such 

 remains from the places where they reach the plains of Siberia (no such bones 

 being ever found in the higher mountains) to the very ocean ; where the frozen 

 earth of the northern plains preserves these remains of southern animals in such 

 perfection, that when I was at Irkuzk, the head and two legs of a true rhinoceros 

 were sent from the river Wilui, with its skin and part of the tendons preserved 

 on them, which are now in the Museum of our Academy, and are fully 

 described and figured in the 17th volume of Nova Commentaria Petropolitana." 



XXXIV. On the Crystallizations observed in Glass. By James Keir, Esq., 



p. 530. 



The peculiar figure of rock crystal has been long observed. Many other 

 substances, as spars, precious stones, pyrites, ores, metals,* salts, water-}- and 

 oil,:}: are also known to affect a uniformity of shape, when they are exposed to 

 certain degrees of heat, cold, fluidity, and other necessary circumstances. 

 From their resemblance in this respect to rock crystal, they are said, when they 

 assume their peculiar forms, to crystallize ; and the regularly shaped bodies, 

 into which these substances concrete, are also called crystals. 



In many substances, when broken, the parts appear to have some determinate 

 figure. This determination of figure, or grain, as it is called^ is obvious in 

 bismuth, regulus of antimony, zinc, and all other metallic bodies, which may 

 be broken without extension of parts ; and though the ductility of gold, silver, 

 lead, and tin, prevents the appearance of the peculiar grains, when pieces of 

 these metals are broken, yet we have reason to believe, that by exposing them 

 to proper circumstances, they also would show a disposition to this species of 

 crystallization, as it may be called, by a further extension of that term ; for 

 Mr. Homberg has observed, that when lead is broken while hot, in which state 

 it is not ductile, a granulated texture appears. Perhaps all homogeneous bodies, 



* Native gold has been found in a crystallized form. M. Rome de Lisle in his Essai de Crystallo- 

 graphie, p. 39i>, says, that he has seen pieces of native gold which were 8 sided solids, like crystals 

 of alum, and one piece which was an hexagonal plate. In Dr. Hunter's museum, some fine speci- 

 mens of crystallized native gold are to be seen. Gold may be crystallized by art also. Some aether 

 having been poured into a solution of this metal in aqua regia, I observed, a few months afterwards, 

 the gold separated from the menstruum, in the form of a distinct polygonous prisms. — Orig. 



"I" The various and regulai- forms of the particles of snow, whicli is nothing else than water 

 crystallized, are well known. — Orig. 



+ The crjstals, formed by cold, in tlie oil of sassafras, have been observed to be very beautiful^ 

 regular, hexagonal prisms. — Orig. 



