Dr. Mac Culloch on Jasper. 65 



by this name ; but it will not be uninstructive to point out a few 

 of the substances, of which the real nature is actually known, 

 which have been indiscriminately included under this popular 

 term. To render such a catalogue complete, would require an 

 access, not only to the specimens themselves, but to a history of 

 their connexions, which is unattainable. 



Siliceous schists, whether found among the primary strata, or 

 among the secondary shales in the vicinity of trap, have been 

 known by the names of black jasper and of striped jasper, ac- 

 cording to the peculiarities of their colours. 



The cherts that are coloured by chlorite or by the brown oxydes 

 of iron, and which are modifications of that chalcedony which, 

 in the same situations, forms heliotrope and brown carnelian, 

 have also been enumerated among the jaspers. 



Veinstones, consisting of various fragments entangled in agate, 

 have also acquired this name among collectors ; and it has 

 indeed frequently been applied in a very vague manner to many 

 agates where their chalcedonic characters were imperfect ; and 

 indeed, to any hard and uniform siliceous rock not included under 

 quartz, and distinguished by brilliancy or intermixture of tints. 



Several of the coloured cherts, often atisiug from the influence 

 of trap upon neighbouring masses of argillaceous, or argillo- 

 calcareous strata, have been, like the siliceous schist of the same 

 origin, included under this head. 



The terra has also been indiscriminately applied to any hard 

 substance of uniform texture, of an aspect more or less earthy 

 yet indurated, and of an ornamental appearance, whatever may 

 have been its origin and connexions, and of however accidental 

 a nature. 



Lastly, I shall only further enumerate all those siliceo-argil- 

 laceous substances, or highly indurated clays, of an uniform and 

 fine texture, which do not easily admit of being ranked with the 

 clay stones or the clink stones of the over-lying family of rocks, 

 though it has occasionally been extended to these. The ap- 

 plication of the term has been chiefly made to those varieties 

 which possess strong colours, or ornamental mixtures of two or 

 more of these. 



Vol. XI. F 



