276 JASPER. 



and it affords an excellent example of the errors which 

 arise in geological reasonings, from an ignorance of 

 the true characters of minerals and rocks. On exa- 

 mining the specimens found in collections, called Hun- 

 garian pitchstones, it will he seen that the greater 

 nninher consist of this jasper. It should he super- 

 fluous to remark, that the same substances occur 

 where trap veins pass through strata capable of under- 

 going the same change. 



In the claystones of the trap family, the progress of 

 induration is commonly such as to cause them to pass, 

 through various stages, to coin pact felspar, as it is 

 commonly called. But, in certain situations, the same 

 claystones are found passing into jasper; being highly 

 indurated, without acquiring the peculiar character of 

 compact felspar. This alteration seems to occur 

 chiefly among the older claystones and porphyries 

 which accompany granite ; and there is no difficulty 

 in tracing its progress, even into the porphyries them- 

 selves, as the cause must also be obvious. Thus there 

 are formed porphyries with a base of jasper : while, 

 as in every other case of such transitions, specimens 

 of doubtful character become the inevitable conse- 

 quence. Such jasper also occurs among the secon- 

 dary claystones when in contact with masses or veins 

 of other traps ; and lastly, as irregular masses among 

 the primary rocks, occupying situations analogous to 

 porphyry or claystone, but presenting no transitions 

 into these, by which to indicate an identity of origin. 

 If nevertheless it is probably the same, we are yet in 

 want of information on this part of the subject. It is 

 thus apparent, that jasper belongs, indifferently, both 

 to the primary and secondary divisions ; but it would 

 be a needless nicety, in this as in other cases, to form 

 two distinctions. 



