464  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull.  86. 
gneiss  and  the  recent  more  finely  grained  gneiss,  more  quartzose  than 
the  other,  which  he  also  designates  as  gneissic  mica-schist  or  as  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  divi- 
sion still  more  recent.  This  division  contains  considerable  thicknesses 
of  beds  designated  by  him  under  the  titles  of  argillaceous  schists,  or, 
rather,  lustrous,  talcose,  micaceous,  and  sericitic  (silk-like)  schists.  As- 
sociated with  these  schists  are  also  found  quartzites,  statuary  and 
Cipolino  marbles,  with  dolomite,  karstenite,  and  sometimes  amphibolic 
rocks  and  serpentines,  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  of  "  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  mineralogical  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  terrane  further- 
more contains  roofing  slates,  as  well  as  lustrous  and  unctuous  schists, 
ordinarily  with  damourite,  sericite  or  pyrophyllite,  but  inclosing  some- 
times chlorite,  steatite,  and  amphibolic  rocks  with  serpentine  and  ophi- 
calcite.  There  are  also  found  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  decompo- 
sition. These  same  schists  also  yield  remarkable  crystals  of  rutile,  as 
well  as  tourmaline,  disthene,  staurolite,  garnet,  and  i>yroxene.  This 
terrane,  which  for  the  rest  appears  diamond-bearing,  was  described 
in  1859  by  Lieber  under  the  name  of  itacolumitic  group.  Eaton,  as 
far  back  as  1832,  had  placed  the  quartzites  and  limestones  forming 
the  lower  members  of  the  group  in  the  primitive  terrane;  while  the 
argillites,  found  toward  the  summit  of  the  same  group,  were  regarded 
as  constituting  the  lower  division  of  the  transition  terrane,  covered, 
according  to  him,  unconformably  by  the  fossiliferous  graywacke  (first 
graywacke)  which  formed  the  upper  division  of  the  same  transition  ter- 
rane. Emmons,  on  his  part,  in  1842,  comprised  in  what  he  called  the 
Taconic  system  all  this  crystalline  series,  as  well  as  the  graywacke; 
but  in  1844  he  separated  the  latter,  in  which  he  had  recognized  the  ex- 
istence of  a  trilobitic  fauna,  giving  it  the  name  of  Upper  Taconic.  Long- 
studies  have  convinced  the  author  that  this  upper  division  is  entirely  in- 
