vANiiisE]  DISCUSSIONS    OF    PRINCIPLES.  465 
dependent  of  the  Lower  Taconic,  with  which  this  fossiliferous  graywacke 
is  in  contact  only  in  relatively  restricted  regions,  while  in  other  locali- 
ties it  rests  directly  on  older  crystalline  terranes.  Seeing,  moreover, 
that  the  Lower  Taconic  is  found  alone  in  a  great  number  of  localities 
from  the  gulf  of  St.  Lawrence  to  Alabama  on  the  south  and  to  lake 
Superior  on  the  west,  and  recognizing  also  the  fact  that  the  Upper  Ta- 
conic really  forms  part  of  the  Cambrian  terrane  (as  for  that  matter  was 
recognized  by  Emmons  in  1860),  the  author  proposed  as  far  back  as 
1878  to  restrict  the  employment  of  the  term  Taconic  to  this  crystalline 
and  infra-Cambrian  series  which  forms  the  lower  Taconic?  of  Emmons 
and  the  itacolumitic  group  of  Lieber,  and  to  give  it  the  name  of  Tacon- 
ian  terrane. 
The  mineralogical  resemblances  existing  among  the  various  crystal- 
line terranes  mentioned  above  are  easy  to  recognize.  The  type  of  rocks 
with  orthose  base  that  appears  in  the  fundamental  granite  and  the 
Laurentian  gneisses  is  also  found  in  the  quartziferous  porphyries  of  the 
Arvonian  and  the  gneiss  of  the  Montalban,  and  less  distinctly  in  the 
feldspathic  rocks  of  the  Taconian.  The  nonmagnesian  micas,  rare  in 
the  fundamental  granite  and  the  Laurentian  gneisses,  are  found  abund- 
antly represented  in  the  gneisses  and  mica-schists  of  the  Montalban, 
as  well  as  in  the  lustrous  schists  found  in  the  Huronian  and  Taconian 
terranes,  and  even  predominate  in  the  latter.  It  is  still  to  be  remarked 
that  the  simple  silicates  of  alumina,  such  as  andalusite,  disthene,  fibrolite, 
and  pyrophyllite,  which  seem  foreign  to  the  oldest  terranes,  abound  in 
the  Montalban  and  also  appear  in  the  Taconian.  At  the  same  time  the 
crystalline  limestones,  the  oxides  of  iron,  and  the  calcareous  and  mag- 
nesian  silicates  are  found  represented,  in  each  terrane  beginning 
from  the  fundamental  granite.  The  chemical  and  mineralogical  differ- 
ences between  these  various  terranes  are  greater  than  the  resemblances, 
which  has  not  prevented  certain  observers  from  confounding  the  recent 
gneiss  with  the  old  gneiss.  In  fact,  the  resemblances  between  the 
Huronian  and  Taconian  terranes  have  led  the  late  Prof.  Kerr,  in  North 
Carolina,  to  refer  the  latter  terrane  to  the  Huronian  terrane.  In  the 
vicinityof  lakes  Superior  and  Huron,  too,  where  the  Laurentian,  Norian, 
Arvonian,  Montalban,  and  Taconian  terranes  are  found  all  at  once,  the 
outcrops  of  the  latter  have  been  confounded  with  those  of  the  Huronian 
terrane  by  Murray  and  other  observers.  In  1873,  however,  the  author, 
distinguishing  between  the  two,  gave  to  the  Taconian  terrane  in  this 
region  the  provisional  name  of  Animikie  series.  Only  later  did  he 
recognize  the  fact  that  this  series,  which  in  certain  localities  rests  un- 
conformably  on  the  Huronian  terrane,  is  only  the  Taconian.  Emmons, 
on  the  contrary,  who  knew  the  existence  in  this  region  of  what  he  called 
the  Lower  Taconic,  thought  that  the  terrane  to  which  in  1855  the  author 
had  given  the  name  Huronian  was  identical  with  this  same  Lower 
Taconic  or  Taconian.  The  differences  between  the  two  terranes  in  the 
basin  of  lake  Superior,  indicated  first  by  Logan  and  afterward  by  the 
Bull.  80- — 30 
