546 JASPER. 



been applied in a very vague manner to many 

 agates where their chalcedonic character was im- 

 perfect; and indeed, to any hard and uniform 

 rock distinguished by brilliancy or intermixture 

 of tints. 



In this work, the name is limited to that sub- 

 stance of which a mineralogical definition is given 

 in the thirteenth chapter, and of which the geo- 

 logical characters are now to be sketched. 



It is said to form a range of mountains in 

 Siberia; but the authority for that assertion is 

 not valid. Practical geologists can be at no loss 

 to account for erroneous statements made on this 

 and similar subjects by ordinary travellers', and 

 even by superficial or rapid geologists. That 

 it occurs in large masses in that country, as well 

 as in the Appenines, imbedded among the pri- 

 mary strata, rests however on authority that can- 

 not be questioned, and it is confirmed by similar 

 observations in our own. In Scotland, it occurs 

 in this manner in the micaceous and argillaceous 

 schists. In these cases, it is an undoubted mem- 

 ber, like serpentine, of the primary class. 



Where strata of quartz rock, containing much 



