DESCRIPTION OF THE MUSEUM. 



of its colours. The varieties of jasper, receive 

 like those of agate, their name from the colour 

 they principally display. One of the most rare is 

 the sanguine jasper, which is of a more or less 

 dark green, spotted with deep red. In the same 

 case we see several specimens of pseudomorphous 

 xyloi'de quartz. These bodies, commonly called 

 petrified wood, were originally trunks or roots 

 of trees, the substance of which has been re- 

 placed by quartz. The substitution takes place by 

 degrees, so that the stony particles are succes- 

 sively lodged in the small cavities, formerly occu- 

 pied by the vegetable matter, in proportion as 

 the latter abandons them, whence the appear- 

 ance of vegetable tissue is preserved. The greater 

 number are from common wood, and marked 

 with concentric zones, which answer to those 

 we see in the transverse section of a tree. Others, 

 and particularly the magnificent trunk which we 

 see in the lower part of one of the cases, were 

 originally palrn-trees; the totally different or- 

 ganization of which is to be traced in the whitish 

 or yellowish ground, sprinkled with little black 

 spots. 



The substances, which follow the quartz, in 

 the twenty-second case, are those "which furnish 

 the rarest precious stones, next to the diamond ; 

 and are the most sought after for their brilliancy 



