SUMMARY    OF    GENERAL   LITERATURE.  71 
studied  and  described  by  Dawson,  who  has  given  it  the  name  Eozoon 
canadense. 
The  Lower  Laurentian  terrane  is  affected  by  many  undulations  that 
have  upraised  the  beds,  rendering  them  at  times  almost  vertical.  The 
mean  direction  of  these  foldings  is  about  north  and  south,  but  sec- 
ondary undulations  from  east  to  west  appear  in  the  region  north  of 
the  Ottawa,  the  only  one  where  thus  far  it  has  been  possible  to  study 
the  intimate  structure  of  this  terrane.  The  beds  of  the  Upper  Lau- 
rentian also  are  upraised  at  high  angles,  but  the  structure  of  this  ter- 
rane, which  has  evidently  undergone  part  of  the  movements  that  af- 
fected the  lower,  has  not  yet  been  studied.  The  lower  terrane  is 
traversed  in  several  localities  by  igneous  rocks,  and  there  have  been 
ascertained  at  least  four  epochs  of  effusion,  three  of  which  are  ante- 
rior to  the  Silurian  period.  These  eruptive  rocks  are  syenites,  quartz- 
iferous  porphyries,  and  dolerites. 
Under  the  name  Huronian  terrane  is  designated  a  series  of  rocks, 
more  or  less  altered,  resting  unconformably  on  the  Lower  Lauren- 
tian terrane,  and  probably  also  on  the  Labradorian  terrane.  This 
series  is  composed  of  quartzites,  more  or  less  chloritic  or  epidotic 
schists,  sometimes  with  impure  serpentines,  and  diorites,  which  con- 
stitute very  important  masses  in  the  series.  The  quartzites,  as  well 
as  the  chloritic  schists,  often  inclose  rolled  pebbles,  many  of  which  are 
derived  from  the  Laurentian  gneiss.  This  Huronian  terrane  com- 
prises, moreover,  a  band  of  about  300  feet  of  granular  limestone, 
which  is  impure  and  often  very  siliceous.  The  Huronian  terrane  on 
Lake  Huron  has  a  thickness  of  about  18,000  feet.  It  is  also  found  on 
the  Ottawa,  and  thence  extends  to  the  west  of  the  Mississippi,  though 
covered  in  large  part  by  Paleozoic  terranes.  It  does  not  seem  to  exist 
in  the  eastern  region  of  Canada,  but  recent  observations  made  on  the 
island  of  Newfoundland  and  in  Nova  Scotia  have  demonstrated  the 
existence  there  of  rocks  that  have  been  referred  to  this  old  terrane 
which  seem  to  correspond  to  the  Primitive  schists  (Urschiefer)  of 
Scandinavia.  No  fossils  have  yet  been  found  in  this  terrane.  Con- 
siderable masses  of  schistose  hematitic  iron  ore  are  inclosed  in  this 
Huronian  terrane  on  the  northeast  shore  of  Lake  Superior,  and  in 
still  greater  abundance  at  the  south,  where  the  famous  iron  mines  of 
Marquette  are  found.  This  terrane  is  more  or  less  affected  by  undu- 
lations anterior  to  the  Silurian  epoch. 
Dana,8  in  1872,  states  that  lithological  evidence  for  the  chrono- 
logical arrangement  of  the  crystalline  rocks  of  New  England  moans 
nothing  until  tested  by  thorough  stratigraphical  investigation.  This 
evidence  probably  means  something  with  respect  to  Laurentian  rocks, 
but  it  did  not  until  the  age  of. the  rocks,  in  their  relations  to  others, 
was  strat  ^graphically  ascertained.      It   may  be   worth  something  as 
