112 OVERLYING AND TRAP ROCKS. 



pose but that of creating mystery, by appearing to 

 imply knowledge unknown to those who are content 

 with common phraseology. He who does not explain 

 himself in received language, wishes to appear more 

 profound than others ; and he who cannot, may fairly 

 be suspected of knowing less. The rocks of this 

 family especially connected with the primary strata, 

 are generally porphyritic, though not invariably 

 so. Though the antiquity presumed from this con- 

 nexion may often be deceptive, they present a very 

 general peculiarity of mineral character, often ap- 

 proaching to that of granite ; the base being frequently 

 granitic, of mixed minerals, and when simple, consist- 

 ing of compact felspar, exclusively; while they also 

 contain metallic veins not occurring among the recent 

 traps. The porphyries of these are far less varied: 

 but I must refer to the Classification for what I need 

 not here describe again. 



The ignorance, or system, of the German geolo- 

 gists had classed the older porphyries among the stra- 

 tified rocks; but they possess all the geological cha- 

 racters of the more recent and Ordinary traps, except- 

 ing as these may have been modified by their peculiar 

 connexions. The supposed strata, when superficial, 

 are rigidly analogous to those of Trap ; and the falla- 

 cious appearances gf interstratification, are either the 

 produce of beds shaped by the primary strata in con- 

 tact, or conformable veins, or else, as in granite, the 

 result of the laminar concretionary structure on the 

 great scale. The practical student who has been be- 

 wildered by the difficulties attending the great deposits 

 of antient porphyry as they have been hitherto de- 

 scribed, will be no less thankful for the facility afforded 

 him by this account of their real nature, than the mere 

 reader, for being thus saved pages of unintelligible 

 description. 



