270  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
domes.  These  relations  are  taken  to  mean  that  the  surrounding 
schistose  rocks  represent  sedimentary  beds  which  have  been  thrust 
aside  by  the  entering  granite.  Along  the  contacts  of  the  Laurentian 
and  Coutchiching  are  found  such  minerals  as  andalusite,  staurolite, 
and  garnet.  Besides  the  granite  masses,  which  cut  all  three  of  the 
previous  series  and  thus  are  later  than  all,  are  also  numerous  diabase 
and  trap  dikes,  which  cut  the  series  mentioned  and  the  granite 
besides. 
In  gall,251  in  1888,  in  describing  the  mines  and  mining  of  Lake 
Superior,  finds  the  rocks  to  consist  of  Laurentian  gneisses  and  granite, 
within  which  are  found  considerable  areas  of  plutonic  and  volcanic 
rocks  and  metamorphic  slates,  considered  to  be  Huronian,  while  over- 
lying these,  chiefly  about  Thunder  Bay  and  Lake  Nipigon,  are  the 
sedimentary  and  volcanic  rocks  of  the  Animikie,  Nipigon,  and 
Keweenian  groups,  which  are  in  an  approximately  horizontal  posi- 
tion and  contrast  markedly  with  the  steeply  inclined  or  almost  ver- 
tical older  rocks.  The  Animikie  formation  is  divisible  into  an  upper 
and  a  lower  portion.  The  chief  character  of  the  lower  division  is  the 
preponderance  of  siliceous  rock,  such  as  chert  and  jasper,  which  are 
often  accompanied  by  ferruginous  dolomite  with  magnetite ;  while 
the  upper  division  is  formed  for  the  most  part  of  black,  soft,  argil- 
laceous argillites,  which  are  occasionally  dolomitic  and  ferruginous, 
and  sometimes  contain  silica  in  such  proportion  as  to  approach  the 
character  of  the  lower  division.  The  thickness  of  the  Animikie  is 
placed  at  12,000  feet.  The  traps  of  the  Animikie  are  concluded  to  be 
intrusive,  frequently  breaking  as  they  do  across  the  beds.  In  one 
case  a  sheet  is  seen  to  divide  into  three  tongues.  The  dark  color  of 
the  upper  division  of  the  Animikie  is  due  to  the  presence  of  carbon. 
Patches  of  basal  conglomerates  are  occasionally  found  at  the  base  of 
the  Animikie,  lying  in  hollows  in  the  old  Archean  sea  bottom,  the 
fragments  consisting  in  general  of  granitic  material. 
Selwyn,252  in  1890,  announces  the  discovery  by  Ingall  of  traces  of 
a  fossil  in  the  Animikie  rocks.  A  part  of  the  impressions  are  pro- 
nounced by  Matthew  to  be  similar  to  Eophyton,  while  for  others  the 
names  T aonichnites  and  Ctenichnites  are  proposed.  Some  of  them 
are  of  similar  origin  with  characteristic  tracks  in  the  Cambrian  rocks 
of  the  St.  John  group  of  New  Brunswick. 
Lawson,253  in  1890,  discusses  the  internal  relations  and  taxonomy 
of  the  Archean  of  central  Canada.  The  Keewatin  and  Coutchiching 
are  again  described,  and  the  characteristic  contacts  which  they  have 
with  the  Laurentian.  To  the  upper  division,  the  Keewatin  and 
Coutchiching,  since  they  are  sedimentary  rocks,  the  principles  of 
stratigraphical  geology  apply,  and  to  cover  these  two  series  is  pro- 
posed the  term  Ontarian,  of  systemic  value.  The  principles  applica- 
ble to  the  lower  division,  the  Laurentian,  are  those  of  eruptive  geol- 
