GRANITE. 83 



undistinguishable from those of the most common 

 trap rocks ; as, on the other hand, examples some- 

 times occur in these, resembling the ordinary granites : 

 while, in these cases, the granite of mica, quartz, and/ 

 felspar, passes into the variety containing hornblende, -/ 

 then into a compound of hornblende and felspar, or 

 the greenstone of the trap family, and lastly into 

 similar ones so minute in texture, as to be absolute 

 specimens of basalt and claystone. And reversely, a 

 claystone in the trap family graduates into a granite of 

 the four usual ingredients; resembling that which is 

 inferior to the primary strata, though it is superior to 

 the secondary. Now as these two families are far 

 distant in time and connexions, and as this forms, in 

 fact, their leading geological characters, we must either 

 discover some mode of always distinguishing them by 

 natural marks, or establish some artificial rule, for the 

 purposes of geology: though, in a rigidly philoso- 

 phical view, having a common origin, and being, thus, 

 fundamentally, the same. If, in most cases, the mi- 

 neral character coincides with the geological one, mi- 

 neralogical granites occurring in the lowest positions, 

 as mineralogical traps do in the highest, this distinc- 

 tion is inapplicable to the cases in question. Either, 

 then, we must unite the whole under one term, or 

 distinguish the two, in every case, by their mineral 

 characters, or, lastly, define them exclusively by their 

 geological positions. 



Under the first of these systems, the result will be * 

 an obvious confusion in geological descriptions, unless #,. 

 we adopt a mode of proceeding for which the science 

 is not prepared, however it may admit of that hereaf- 

 ter. If the distinction be made purely mineralogical, 

 it will become impossible to know, whether the terms 

 "trap," and "granite," are always applied, respectively^ 



G2 



