274 



JASPER. 



relied on ; while the name jasper has been applied in 

 so vague a manner as to lead to great confusion. Be- 

 ing a commercial as well as a mineralogical term, it is 

 impossible, without a sight of the specimens in ques- 

 tion, to understand always what is intended by it. It 

 is a sufficient example of this laxity, that even the cal- 

 careous stalagmites of Sicily have been called by this 

 name ; but it will be useful to point out a few of the 

 substances indiscriminately included under it. Sili- 

 ceous schists, whether from the primary or the secon- 

 dary strata, have been called black jasper and striped 

 jasper, according to their colours ; as have the co- 

 loured cherts produced from argillaceous limestones 

 accompanying them. The cherts coloured by chlorite 

 and by the brown oxydes of iron, being modifications 

 of that chalcedony which forms heliotrope and brown 

 carnelian* have also been enumerated among the jas- 

 pers ; as have veinstones consisting of fragments en- 

 tangled in coloured chalcedony or agate, together with 

 many other hard stones, which, with an uniform tex- 

 ture, possessed an aspect more or less earthy, and an 

 ornamental appearance, whatever may have been their 

 origin and connexions. Further, it has been applied 

 to the highly indurated clays of a fine texture which 

 are associated with trap without belonging to it, and, 

 more rarely, with granite ; as also to real trap clay- 

 stones when presenting the same peculiar characters; 

 yet being commonly limited to highly coloured varieties. 

 To these two last substances ought this term to be 

 confined, as they cannot well be expressed by any 

 other, and as all the preceding ones may easily be 

 ranked nnder the several heads to which they belong. 

 Thus the term jasper will become useful in a geolo- 

 gical view ; without innovation, and merely by limit- 

 ing it to one of the best characterized of the various 

 substances to which it is indiscriminately applied. If 



