452 GEOLOGY. 



1. Granites (f.n.)/ consisting largely of quartz and feldspar of any- 

 kind, with or without mica, hornblende, pyroxene, or other minerals. 

 This differs from the present common use in not regarding mica as an 

 essential constituent, and in not distinguishing between alkali feldspars 

 and calcic feldspars, thus broadening the class. 



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 horn- 

 blende a subordinate place, and in embracing rocks with calcic feldspars, 

 thus broadening the class. 



3. Diorites (f.n.), consisting predominantly of hornblende and sub- 

 ordinately of feldspar of any kind, with which there may be mica, pyrox- 

 ene, or other minerals. This is nearly the present use except that 

 any kind of feldspar may form the subordinate element. 



4. Gahhros (f.n.), consisting predominantly of pyroxene and subor- 

 dinately of feldspar of any kind, with or without other minerals. This 

 nearly coincides with one of the various present uses of the term except 

 that the range of the feldspar is increased. 



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

 mineral not distinguishable as hornblende or pyroxene, with subordi- 

 nate elements of feldspar of any kind, and with or without other accessory 

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

 ferromagnesian, but cannot be satisfactorily identified as either horn- 

 blende or pyroxene, although it may probably be one of these. In 

 other words, the dolerites (deceptive) embrace the w^hole diorite-gabbro 

 group when too obscure for separation. 



6. Peridotites, ' consisting predominantly of olivine and ferromag- 

 nesian minerals, without feldspar, or with very httle. 



7. Pyroxenite, consisting essentially of pyroxene without feldspar 

 or olivine. 



8. Hornhlendite, consisting essentially of hornblende without feld- 

 spar or olivine. 



11. The Aphanites may be non-porphyritic or porphyritic. 

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

 felsites; when dark-colored, as basalts. 



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. 



