vanhise.]  DISCUSSIONS    OF    PRINCIPLES.  467 
which  is  sometimes  called  the  primitive  gneiss  series.  It  consists  essen- 
tially of  obscurely  foliated  or  stratiform  granitic  or  syenitic  gneiss. 
The  prevailing  colors  of  the  Lower  Laurentian  gneiss  are  grayish  and 
reddish.  In  some  districts  the  Laurentian  rocks  are  cut  by  dikes  of 
greenstone  or  trap.  In  the  Upper  Laurentian  are  placed  both  the  anor- 
thosite  rocks  and  the  limestone-bearing  series  of  eastern  Ontario.  The 
anorthosites,  which  are  considered  by  some  as  eruptives  and  others  as 
bedded  rocks  interlaminated  with  the  limestones,  may  be  in  part  of  both 
origins.  Anorthosites,  after  spreading  out  upon  the  surface  of  the  earth 
or  the  bottom  of  the  sea,  may  have  become  incorporated  in  a  conformable 
manner  with  the  contemporaneous  deposits,  while  others  may  have 
flowed  over  preexisting  rocks  which  were  not  disturbed.  Between  the 
Upper  and  Lower  Laurentian  there  may  be  a  general  want  of  conformity. 
The  Upper  Laurentian  contains  metallic  ores  and  very  numerous  min- 
erals, which  are  not  found  in  the  Lower  Laurentian.  The  gneisses  of 
the  Upper  and  Lower  Laurentian  often  have  a  close  resemblance.  As 
the  evidence  is  so  strongly  in  favor  of  the  aqueous  origin  of  a  part  of 
the  Upper  Laurentian  at  least,  this  lends  support  to  the  view  that  even 
the  primitive  gneisses  may  have  been  formed  by  the  action  of  water 
during  some  early  condition  of  the  earth,  of  which  we  can  form  but 
little  conception  judging  by  the  later  stages  of  its  history.  Eozoon  is 
regarded  as  a  myth,  and  the  limestones,  iron  ores,  graphite,  and  apa- 
tite are  not  considered  as  evidence  of  the  existence  of  animals  or  plants 
in  Laurentian  times.  The  limestones  may  be  chemical  sediments;  the 
graphite  and  apatite  occur  principally  as  vein  matter;  the  iron  ores 
occur  in  greater  masses  than  in  deposits  of  organic  origin,  and  their 
mode  of  occurrence  is  opposed  to  any  theory  of  this  kind.  The  Upper 
Laurentian  rocks  seem  to  be  much  more  limited  in  geographical  extent 
than  the  Lower  Laurentian. 
The  Huronian  system  in  Canada  has  a  great  thickness  and  variety 
of  strata,  for  the  most  part  crystalline,  but  in  a  less  degree  than  the 
Laurentian,  together  with  many  unstratified  igneous  masses.  Like  the 
Laurentian  it  is  Azoic,  or  devoid  of  any  trace  of  organic  life,  so  that  the 
distinction  between  the  two  systems  is  based  entirely  on  lithological 
grounds.  The  difference  in  this  respect  is  great,  and  is  easily  recognized 
by  those  who  have  paid  any  attention  to  geology.  The  prevailing  dark 
greei  l  and  gray  colors  of  the  Huronian  offer  a  marked  contrast  to  the  lighter 
grays  and  reddish  grays  of  the  Laurentian.  The  latter  are  massive  and 
coarsely  crystalline,  while  the  former  are  usually  fine  grained  and  schis- 
tose or  fissile,  this  cleavage  structure  constituting  a  striking  difference 
from  the  solid  Laurentian.  .There  are  some  exceptions  to  this  rule,  such 
as  the  light-colored  quartzites  and  the  granites  and  syenites  of  the 
Huronian,  to  be  noticed  further  on.  The  change  in  passing  from  one  to 
the  other  is  often  sudden  and  complete,  but  sometimes  beds  of  passage 
are  met  with.  The  Huronian  is  the  great  metalliferous  system  of  Can- 
ada.   Although  the  Huronian  strata  have  generally  been  thrown  into 
