60 GEOLOGY 



I. The phaneritcs may be further classified by their chief mineral con- 

 stituents as follows: 



1. Granites (f. n.) 1 , consisting largely of quartz and feldspar of any kind, 

 with or without mica, hornblende, pyroxene, or -other minerals. This differ- 

 from the present common use in not regarding mica as an essential constituent, 

 and in not distinguishing between alkali feldspars and calcic feldspars. The 

 term therefore includes more than the term as heretofore used. 



2. Syenites (f. n.), consisting predominantly of feldspar of any kind, 

 with subordinate amounts of hornblende, mica, or pyroxene, but with little 

 or no quartz. This differs from the common use in giving hornblende a 

 subordinate place, and in embracing rocks with calcic feldspars. 



o. Diorites (f. n.), consisting predominately of hornblende and subor- 

 dinately of feldspar of any kind, with which there may be mica, pyroxene, 

 or other minerals. This is nearly the present use, except that any kind of 

 feldspar may be the subordinate mineral. 



4. Gabbros (f. n.), consisting predominantly of pyroxene and subordinately 

 of feldspar of any kind, with or without other minerals. This nearly coin- 

 cides with one of the various present uses of the term except that the range 

 of the feldspar is increased. 



5. Dolerites 2 (f. n.), consisting predominantly of any ferromagnesian 

 mineral not distinguishable as hornblende or pyroxene, with subordinate 

 amounts of feldspar of any kind, and with or without other accessory minerals. 

 A name to be used when the dominant mineral is clearly ferromagrresiaii. 

 but cannot be satisfactorily identified by the eye, as either hornblende or 

 pyroxene, although it may be probably one of these. In other words, the 

 dolerites (deceptive) embrace the whole diorite-gabbro group when too 

 obscure for separation. 



6. Peridotites, consisting predominantly of olivine and ferromagnesian 

 minerals without feldspar, or with very little. 



7. Pyroxenites, consisting essentially of pyroxene without feldspar or 

 olivine. 



8. Hornblendites, consisting essentially of hornblende without feldspar or 

 olivine. 



II. The aphanites may be non-porphyritic or porphyritic. 



(a) Non-porphyritic aphanites, when light-colored, may be classed as 

 felsites', when dark-colored, as basalts. 



(b) The porphyritic aphanites or porphyries, when light-colored, are 

 leucophyrcs] when dark-colored, melaphyres. They may be classified fur- 

 ther, according to the kind of phenocryst (distinct crystal) imbedded in 

 the aphanitic ground-mass, as 



Quartz-porphyries, or quartzophyres; 



1 The initials f . n. (field names) are introduced to show that the term is 

 used in the broad field sense proposed. 



2 Added by the authors of this work. 



