van  n ist:.]  DISCUSSIONS    OF    PRINCIPLES.  463 
rocks  which  pass  into  the  state  of  quartziferous  porphyry,  with  which, 
however,  certain  amphibolic  rocks  are  intercalated,  as  well  as  sericitic 
schists,  quartzites,  oxides  of  iron,  and  more  rarely  crystalline  lime- 
stone. This  terrane,  indicated  for  the  first  time  by  Hicks,  in  1878,  in 
Wales,  is  regarded  by  Charles  Hitchcock  as  forming  in  North  America 
the  lower  part  of  the  Hiironian  terrane. 
(4)  Huronian.  This  name  Avas  given  by  the  author  in  1855  to  a  ter- 
rane already  recognized  in  North  America,  where  it  rests  unconform- 
ably  either  on  Laurentian  gneisses  or  on  Arvonian  hornston.es.  It  com- 
prises, besides  quartzose,  epidotic,  chloritic,  and  calcareous  schists, 
also  masses  of  serpentine  and  lherzolite,  as  well  as  euphotides,  which 
represent  in  this  terrane  the  norites  of  the  Norian  terrane,  with  which 
they  are  sometimes  confounded  under  the  common  name  of  gabbro. 
This  terrane  predominates  in  the  Alps,  where  it  forms  the  series  of 
red  stones  (pietre  verdi). 
(5)  Montalban.  The  studies  of  von  Hauer,  published  in  1868,  on  the 
eastern  Alps,  and  those  of  Gerlach  on  the  western  Alps,  published  the 
.year  following,  agree  in  recognizing  in  these  regions  two  gneissic  ter- 
ranes,  that  is  to  say,  an  old  or  central  gneiss  and  a  young  or  recent 
gneiss;  the  latter,  which  is  very  distinct  from  the  old  gneiss  from  a 
petrographic  point  of  view,  being  accompanied  by  micaceous  and  am- 
phibolic schists.  The  studies  of  Gastaldi,  published  in  1871,  and  those 
of  Neri,  published  in  1874,  while  confirming  Hauer  and  Gerlach's  re- 
sults, have  furnished  more  details  on  these  terranes  and  their  litho- 
logic  characters.  It  is  proper  to  remark  here  that  all  these  observers 
seem  to  be  agreed  in  placing  the  horizon  of  the  greenstones  (Huronian) 
between  the  old  gneiss  (Laurentian)  and  the  young  gneiss. 
Before  he  had  knowledge  of  the  first  observations  of  these  scientists, 
the  author,  in  accordance  with  his  own  studies  in  North  America,  was 
led  to  identical  conclusions,  and  in  1870  he  announced  the  existence  of 
a  series  of  young  gneisses,  quite  distinct  from  the  old  gneisses,  and 
accompanied  by  crystalline  limestones  and  by  micaceous  and  amphi- 
bolic schists.  To  this  terrane,  in  view  of  its  great  development  in  the 
White  mountains  of  New  Hampshire,  he  gave  in  1871  the  name  of 
Montalban.  This  series,  for  the, rest,  appears  identical  with  the  young 
gneiss  of  the  Alps,  with  gneisses  and  mica-schists  called  Hercynian  in 
Bavaria,  with  the  granulites  with  dichroite  rocks,  mica-schists,  and 
lherzolite  of  the  Erzgebirge  in  Saxony,  and  similar  rocks  in  the  moun- 
tains 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  endogenous  masses  of  pegma- 
tite, often  inclosing  emerald,  tourmaline,  and  tin,  uranium,  tantalum, 
and  niobium  ores. 
Gastaldi,  in  a  memoir  published  in  1874,  declares  that  the  greenstones, 
properly  so  called,  lie  between  the  old  porphyroid  and  fundamental 
