LAKE  SUPERIOR  REGION.  259 
conglomerates,  the  total  thickness  being  more  than  16,000  feet.  The 
total  thickness  of  the  series  at  Mamainse  and  Michipicoten  is  believed 
to  be  at  least  20,000  feet.  As  to  the  relations  of  the  horizontal  Sault 
sandstone  to  the  Upper  Copper-bearing  series,  a  place  was  found  on 
the  south  of  Point  aux  Mines  where  the  Mamainse  series  adjoins  the 
Laurentian  rocks.  The  lowest  member  of  the  former  is  unconform- 
ably  overlain  by  thin-bedded  bluish  and  yellowish  gray  sandstone, 
striking  N.  50°  E.,  and  dipping  18°  NW.  The  lowest  layer  is  a  con- 
glomerate with  granitic  and  trappean  bowlders,  and  is  followed  by 
thin-bedded  sandstones,  and  these  by  thin  shaly  layers. 
Macfarlane,-8  in  1868,  describes  the  rocks  of  the  north  and  east 
shores  of  Lake  Superior.  He  here  finds  four  formations — the  Lauren- 
tian, Huron ian,  Upper  Copper-bearing  rocks,  and  St.  Mary  sandstone. 
The  most  prevalent  rocks  of  the  Laurentian  series  are  of  a  massive 
crystalline  character,  more  of  a  granitic  than  of  a  gneissic  nature. 
Almost  equally  frequent  with  the  granitic  and  gneissic  rocks  are  ag- 
gregates of  rocks  which  can  be  described  as  brecciated  and  intrusive, 
gneissic,  granitic,  and  syenitic  rocks.  In  these  the  order  of  age  is 
always  from  basic  to  acidic.  In  one  case  fragments  of  hornblende 
schists  are  found  inclosed  in  syenitic  granite,  which  is  cut  by  granite 
dikes  of  different  ages.  It  is  believed  that  these  rocks  are  wholly  of 
igneous  origin,  representing  a  single  period  of  time — the  basic  rock 
first  solidified ;  they  were  then  rent  off,  broken  up,  and  the  crevices 
filled  with  more  siliceous  material,  which  gradually  solidified,  after 
which  occurred  another  general  movement  with  further  intrusion  of 
the  most  siliceous  materials. 
In  the  Huronian  series  is  placed  diabase,  augite  porphyry,  cal- 
careous diabase,  diabase  schist,  greenstone  and  greenstone  slate, 
chlorite  schist,  quartzite,  hematite,  greenstone  breccia,  and  slate  con- 
glomerate. The  slate  conglomerate  frequently  contains  granite  peb- 
bles which  are  in  roundish,  lenticular,  bent,  long-drawn-out  masses, 
with  a  diabase  schist  or  greenstone  slate  matrix.  These  rocks  locally 
have  a  sedimentary  appearance,  but  are  believed  to  be  due  to  the  sub- 
sequent intrusion  of  the  Huronian  rocks,  which  have  caught  granite 
fragments  in  them  and,  by  movement  and  heat,  have  softened  and 
much  distorted  the  contained  fragments.  It  follows  that  far  the 
greater  number  of  the  Huronian  rocks  are  regarded  as  purely  igneous. 
In  the  Upper  Copper-bearing  series  are  distinguished  melaphyre 
of  various  kinds — melaphyre  breccia,  porphyrite,  porphyritic  con- 
glomerate, felsite  tuff,  polygenous  conglomerate,  and  sandstone.  The 
polygenous  conglomerate  contains,  at  Mamainse,  fragments  chiefly 
of  granite,  gneiss,  quartzite,  greenstone,  and  slate,  while  some  of  the 
newer  contain  abundant  bowlders  of  melaphyre  and  amygdaloid. 
The  igneous  rocks  and  sandstones  are  regularly  interst  rati  lied  with 
