408  PRE-CAMBRIAN    GEOLOGY   OF    NORTH    AMERICA. 
Laurentian  gneiss,  and  from  which  emanates  a  complexity  of  dikes, 
the  whole  being  supposed  to  be  of  Huronian  age.  The  immediate 
contact  of  the  gneiss  with  the  overlying  rocks  has  not  been  observed. 
The  gneiss  between  Mississagui  and  St.  Marys  rivers  has  been 
much  disturbed  by  intrusive  granite  and  greenstone,  and  it  is  difficult 
to  make  out  how  the  stratified  portions  are  related  to  one  another. 
Near  Les  Grandes  Sables  a  gray  quartzite,  supposed  to  be  the  lowest 
Huronian,  abuts  against  one  mass  of  gneiss,  and  runs  under  another 
and  appears  to  be  much  broken  by  and  entangled  among  the  intrusive 
rock.  On  Lake  Temiscamang  the  Laurentian  gneiss  is  followed  by  a 
slate  conglomerate  which  contains  pebbles  and  bowlders,  sometimes 
a  foot  in  diameter,  of  the  subjacent  gneiss.  The  Huronian  of  Lake 
Huron  is  correlated  with  the  lower  copper-bearing  rocks  of  Lake 
Superior.  Several  detailed  sections  are  described.  The  general  sec- 
tions represent  the  Huronian  series  as  resting  unconf ormably  upon  the 
Laurentian. 
Logan,17  in  1865,  states  that  the  horizontal  strata  which  form  the 
base  of  the  Lower  Silurian  in  western  Canada  rest  upon  the  upturned 
edges  of  the  Huronian  series,  which  in  its  turn  unconf  ormably  over- 
lies the  Lower  Laurentian.  The  Huronian  is  believed  to  be  more  re- 
cent than  the  Upper  Laurentian  series,  although  the  two  formations 
have  never  yet  been  seen  in  contact. 
Bell,18  in  1878,  reports  on  geological  researches  north  of  Lake 
Huron  and  east  of  Lake  Superior,  including  Lake  Nipissing.  He 
finds  the  rocks  along  the  whole  northeast  coast  of  Georgian  Bay,  a 
distance  of  125  miles,  to  belong  to  the  Laurentian  series.  They  consist 
principally  of  varieties  of  gneiss,  occasionally  interstratified  with 
bands  of  hornblendic  and  micaceous  schists.  The  crystalline  lime- 
stones are  also  found,  as  well  as  stratified  diorites,  trap  rocks,  and 
granite  veins.  The  rocks  have  no  uniform  strike  and  are  contorted 
into  many  anticlines  and  synclines.  The  crystalline  limestones  of 
Georgian  Bay  and  Lake  Nipissing  are  regarded  as  belonging  in 
three  and  possibly  more  crystalline  bands.  Associated  with  the  lime- 
stone are  sometimes  found  chert,  conglomerate,  quartzite,  and  mag- 
netic iron  ore.  A  junction  of  the  granite  with  the  Huronian  quartzite 
and  hornblende  schist  is  mentioned. 
Selwyn,19  in  1884,  west  of  Wahnahpitae  River,  on  the  Canadian 
Pacific  Railway,  for  80  miles  finds  Laurentian  rocks,  which  consist 
of  felsites  or  felsitic  quartzites,  thin-bedded  quartzites  which  hold 
angular  fragments  of  granite  and  gneiss,  diorite,  and  diabase,  with  a 
series  of  coarse  and  fine  fragmental  beds  varying  in  character  from  a 
fine  ash  to  coarse  agglomerate. 
Irving,20  in  1887,  summarizes  the  information  of  the  Canadian  Sur- 
vey with  reference  to  the  Huronian  of  Lake  Huron,  and  describes  a 
contact  near  Thessalon  River  between  the  underlying  gneissic  series 
