vanhise.]  LAKE    HURON    TO    LAKE    TEMISCAMANG.  37 
probable  equivalent  of  the  copper-bearing  group  of  lake  Superior. 
The  series  is  divided  into  rocks  of  sedimentary  and  rocks  of  eruptive 
origin.  The  sedirnentaries  consist  of  sandstones,  conglomerates,  slates, 
and  limestones.  The  greenstones  are  of  igneous  origin,  and  are  of  two 
classes,  intrusives  and  overflows.  The  intrusives  are  in  part  as  shi 
and  in  part  as  dikes.  The  various  kinds  of  sedimentary  beds  grade 
into  each  other,  while  the  greenstones  do  not  thus  grade  into  the  sedi- 
ments, and  therefore  present  a  strong  contrast  to  the  real  sedimentary 
beds.  The  dikes  and  overflow  sheets  arc  lithologieally  alike,  and  the 
dikes  reveal  a  history  which  has  two  or  three  episodes.  The  chief  dif- 
ference in  the  copper-bearing  rock  of  lakes  Union  and  Superior  seems 
to  lie  in  the  great  amount  of  amygdaloidal  trap  in  the  latter,  and  of 
white  quartz  or  sandstone  in  the  former,  but  there  are  strong  points  of 
resemblance,  so  it  is  highly  probable,  if  not  almost  certain,  that  they 
are  equivalent  and  beneath  the  lowest  fossiliferous  deposits.  On  the 
east  and  west  the  series  seems  to  repose  on  granite. 
Murray,38  in  1850,  gives  the  result  of  a  survey  of  the  Spanish  river. 
Upon  this  stream  he  finds  exposed  a  granitic  Or  metamorpnic  group  and 
a  quartz-rock  group.  The  latter  contains  quartzites,  slates,  and  con- 
glomerates, holding  sometimes  pebbles  of  jasper,  but  more  often  of  sye- 
nite or  granite,  as  well  as  limestones  and  dikes  and  beds  of  intrusive 
greenstones,  and  can  scarcely  be  less  than  10,000  feet  thick.  The  gra- 
nitic group  appears  to  rise  from  beneath  the  metamorpnic  group  at  two 
places. 
LOGAN,39  in  1852,  states  that  on  lake  Huron  the  Lower  Silurian  group 
rests  unconformable  upon  a  siliceous  series,  containing  one  band  of 
limestone  about  150  feet  in  thickness,  having  leaves  of  chert,  but  with- 
out discovered  fossils.  The  series  is  the  copper-bearing  rocks  of  that 
district,  is  interstratified  with  igneous  masses,  and  has  a  thickness  of 
at  least  10,000  feet;  it  is  supposed  to  be  the  Cambrian  epoch.  The 
gneissoid  group  is  probably  still  older,  and  its  condition  is  such  as  to 
make  it  reasonable  to  suppose  that  it  consists  of  altered  aqueous  depos- 
its. 
Murray,7  in  1857,  describes  several  of  the  more  important  streams 
between  Georgian  bay  and  lake  Nipissing.  They  embrace  two  of  the 
oldest  recognized  geological  formations,  the  Laurentian  and  Huronianj 
the  rocks  of  the  latter  are  more  recent  and  have  been  observed  to  pass 
unconformably  below  the  lowest  of  the  fossiliferous  strata  of  the  ►Silu- 
rian system.  The  contorted  gneiss  of  the  Laurentian  series,  with  its 
associated  micaceous  and  hornblendic  schists,  spreads  aver  the  country 
to  the  south  and  east,  while  the  slates,  conglomerates,  limestones, 
quartzites,  and  greenstones  of  the  Huronian  occupy  the  northern  and 
western  parts.  The  difference  in  lithological  character  between  the 
two  formations  is  always  sufficiently  apparent,  bui  though  both  were 
found  a  short  distance  apart,  the  immediate  point  of  contact  was  always 
