SUMMARY   OF   GENERAL  LITERATURE.  89 
schists,  and  lherzolite  of  the  Erzgebirge  in  Saxony,  and  with  similar 
rocks  in  the  mountains  of  Scotland.  This  Montalban  terrane  in 
North  America  includes  not  only  crystalline  limestones  but  beds  of 
lherzolite  and  serpentine,  quite  like  the  Huronian  and  the  Laurentian. 
It  is  also  in  this  series  that  are  found  most  of  the  "  filonian  "  or  endog- 
enous masses  of  pegmatite  often  inclosing  emerald,  tourmaline,  and 
tin,  uranium,  tantalum,  and  niobium  ores. 
Gastaldi,  in  a  memoir  published  in  1874,  declares  that  the  green- 
stones, properly  so  called,  lie  between  the  old  porphyroid  and  funda- 
mental gneiss  and  the  recent  more  finely  grained  gneiss,  more  quartz- 
ose  than  the  other,  which  he  also  designates  gneissic  mica  schist  or 
very  micaceous  gneiss  passing  into.mica  schist  and  often  amphibolitic, 
the  two  gneissic  series  being,  according  to  him,  easy  to  distinguish. 
To  these  two  divisions  above  the  old  gneiss  Gastaldi  added  a  third 
division  still  more  recent.  This  division  contains  considerable  thick- 
nesses of  beds  designated  by  him  argillaceous  schists,  or,  rather, 
lustrous,  talcose,  micaceous,  and  sericitic  (silklike)  schists.  Associ- 
ated with  these  schists  are  found  quartzites,  statuary  and  Cipolino 
marbles,  with  dolomite,  karstenite,  and  sometimes  amphibolic  rocks 
and  surpentines,  the  presence  of  which  in  this  division,  and  even  in 
the  recent  gneisses,  as  well  as  in  the  greenstones,  properly  so  called, 
seemed  to  him  to  justify  the  name  "  zone  of  greenstones,"  often  given 
by  Gastaldi  to  the  whole  of  this  triple  group  of  crystalline  schists 
which  he  recognized  as  being  less  old  than  the  central  gneiss. 
(6)  Taconian.  This  third  division,  to  which  Gastaldi  gave  no  dis- 
tinctive name,  has,  as  is  known,  a  very  interesting  history  in  Italian 
geology.  A  terrane  having  at  the  same  time  the  same  horizon  and  the 
same  minera logical  characters  is  found  greatly  developed  in  North 
America,  where  it  comprises  quartzites  (often  schistose  and  sometimes 
flexible  and  elastic)  and  crystalline  limestones,  yielding  statuary  and 
Cipolino  marbles.  There  are  also  found  there  deposits  of  magnetitic 
and  of  hematitic  iron,  as  well  as  important  beds  of  limonite,  the  latter 
being  epigenic  either  from  pyrites  or  from  carbonate  of  iron,  two 
species  which  by  themselves  form  considerable  masses.  This  terrain1 
furthermore  contains  roofing  slates,  as  well  as  lustrous  and  unctuous 
schists,  ordinarily  with  damourite,  sericite,  or  pyrophyllite,  but  inclos- 
ing sometimes  chlorite,  steatite,  and  amphibolic  rocks  with  serpentine 
and  ophicalcite.  There  are  also  among  these  schists,  which  are  found 
at  diverse  horizons  in  this  terrane,  beds  visibly  feldspathic,  with 
others  of  ill-defined  nature,  which  are  transformed  into  kaolin  by 
aerial  decomposition.  These  same  schists  also  yield  remarkable  crys- 
tals of  rutile  as  well  as  tourmaline,  disthene,  staurolite,  garnet,  and 
pyroxene.  This  terrane,  which  appears  to  be  diamond  bearing,  was 
described  in  1859  by  Lieber  under  the  name  Itacolumitic  group. 
Eaton,  as  far  back  as  183:2,  had  placed  the  quartzites  and  limestones 
