170 DOMAIN II. SILICEOUS. 



obvious from the description which he has given 

 of his corneusjissiliS) that he did not mean to sig- 

 nify by that name our schistose-porphyry, which, 

 as it seems, he did not know r but the hornblend- 

 schiefer (hornblende-slate of Kirwan). 



" Other authors, as Born, Ferber, receive under 

 this name, sometimes different varieties of the 

 thonschkfer (argillaceous slate), and sometimes 

 glimmer schiefer (micaceous slate). 



" The first oryctologist who has awakened the 

 attention of naturalists to the schistose-porphyry, 

 and given of it an accurate description, was Char- 

 pentier, in his Mineralogical Geography of the 

 Electoral Dominions of Saxony. At the same 

 time he gave to it exclusively the name of horn- 

 slate, in which he was followed by most of the Ger- 

 man mineralogists. But Werner thought other- 

 wise. He left this name at first to that species of 

 stone, which afterwards has been called kiesel- 

 chiefer (siliceous slate); and denominated that 

 which is the subject of the present essay schistose- 

 porphyry , in order to distinguish it as a peculiar 

 species of porphyry. In fact, it exhibits the mi- 

 neralogical character of porphyry : as it princi- 

 pally consists of an homogeneous, hard, siliceous 

 and argillaceous aggregate, in which, though but 

 sparingly, and singly, are interspersed small la- 

 of feldspar, besides minute grains of horn- 



