c.  Porphyritic;  the  feldspar  in  whitish  or  ^eenish  white  crystals  dis-
seminated through  a  fine-grained  base,  making  a  greenish  **  porphyry."

d.  Pyroxenic;  containing  some  disseminated  pyroxene,  e.  MagnetUic;
containing  magnetite  or  titanic  iron.  Occurs  in  the  Urals;  in  Orange,
west  of  New  Haven,  Conn.,  both  massive  and  porphyritic;  of  blsu^k
color  in  dikes  at  Compton  Falls,  N.  H.  (Hawes).  llie  porphyritic
variety— a  metamorphic  rock — afforded  Hawes.  »ilica  48*61,  alumina
17*81,  iron  scsquioxide  0'25,  iron  protoxide  8*46,  manganese  protoxide
0*20,  lime  11*16,  magnesia  776,  soda  2*77,  potash  0*47,  water  1*63,
titanium  dioxide  1*35  =  100*47;  G.  =  3  01;  the  crystals  of  the  porphy-
ritic variety,  according  to  an  incomplete  analysis  by  E.  S.  Dana,  consist
of  anorthite ;  they  are  mostly  altered,  and  prolmbly  in  the  state  of
saussurite.
Epidioryte  consists  of  plagioclase  with  hornblende,  some  quartz,  a


DESCRIPTIONS  OF  ROCKS.  483

Httle  orthoclase,  and  some  pyroxene.    Silica  56  p.  c.     Chhrophyre  of
Quenast,  Belgium,  is  related.
Anaugite-dityryte  containing  laibradaritsin  place  of  oligoclasc  is  iden-
tical in  mineral  composition  with  gabbro  and  basalt.
4.  Andesyte.  {Hornhlende-andesyte,) — Consists  of  oligo-
clase  or  andesite  and  hornblende,  with  often  some  orthoclase
Qr  sanidin,  and  biotite.  Sometimes  porphjrritic.  Color
usually  dark  to  light  green,  and  gray,  sometimes  purplish;
aspect  more  or  less  trachytic.  Some  glass  in  the  base,  as
in  lavas.  Silica  59-63  p.  c.  G.  =  2-6-2-7.  Texture  varies
from  coarsely  crystalline  to  microcrystalline,  trachytic,
rhyolitic,  glassy,  scoriaceous,  and  at  Washoe,  Nevada,  these
wide  extremes  exist  in  the  same  eniptive  mass,  according
to  Hague  and  Iddings.
6.  Dacyte.  {Quariz-n^idesyte.) — Like  the  above,  but
containing  disseminated  quartz  grains,  and  sometimes
quartzophyric.  Silica  65  to  70  p.  c.  Often  graduates  into
tne  orthoclase  rock,  rhyolyte.
