102  PRE-CAMBRIAN  ROCKS   OF   NORTH   AMERICA.  [bull.  86. 
Vermilion  regions,  but  resemble  those  of  the  Animikie  series  and  are 
therefore  perhaps  Huronian,  while  the  Gogebic  iron-bearing  strata  are 
not. 
Wadsworth,113  in  1890,  gives  a  general  account  of  the  geology  of 
the  Marquette  and  Keweenaw  districts  based  upon  his  own  and  other 
works.  The  Azoic  system  includes  fragmental  and  eruptive  rocks. 
Among  the  former  are  various  argillites  and  schists  of  the  Marquette 
district.  Among  the  eruptive  rocks  are  placed  the  jaspilites  and  their 
associated  ores,  with  the  exception  of  certain  soft  iron  ores  of  chemical 
origin.  The  Keweenawan  is  again  placed  as  a  part  of  the  Potsdam, 
since  the  first  lava  flow  found  on  Keweenaw  point  flowed  over  the 
Eastern  sandstone.  Subsequently  there  has  been  a  fault  line  or  fissure 
running  near  the  contact  of  the  sandstones  and  lavas.  This  fault  is 
regarded  as  normal  and  it  accounts  for  the  fact  that  sometimes  the 
lavas  and  sometimes  the  associated  conglomerates  are  brought  in  con- 
tact with  the  Eastern  sandstone  along  the  fault  line. 
Wadsworth,114  in  1891,  modifies  somewhat  the  foregoing  account  of 
the  Azoic  system.  A  portion  of  the  jaspilites  and  associated  iron  ores 
are  still  held  to  be  eruptive,  but  it  is  suggested  that  even  for  these 
supposed  nonfragmental  jaspilites  of  Ishpeming  and  Negaunee,  their 
present  relations  may  be  due  to  sedimentary  and  chemical  action  and 
the  squeezing  together  of  the  jaspilite  and  schist.  The  jaspilite  and 
ore,  with  the  associated  quartzites,  occurring  at  Cascade,  Kepublic, 
Humboldt,  and  a  part  of  those  at  Ishpeming  and  Negaunee,  as  well  as 
those  of  the  overlying  quartzites  and  schists,  are  sedimentary.  In  the 
Marquette  district  there  are  three  distinct  geological  formations  or  ages 
in  ascending  order  as  follows:  First,  the  hornblende-schist  and  granite 
of  Cascade  or  Palmer  and  the. nonfragmental  jaspilite  aud  ore  of  lsh> 
peniing  and  Negaunee — the  Cascade  formation.  Second,  the  frag- 
mental jaspilite  and  ore,  with  their  associated  quartzites  and  schists  of 
Cascade,  Republic,  Humboldt,  Ishpeming,  Negaunee,  and  elsewhere — 
the  Republic  formation.  Third,  the  overlying  conglomerates,  quartz- 
ites, and  schists  of  Cascade,  Republic,  Holyoke,  and  elsewhere — the 
Holyoke  formation. 
Above  the  detrital  Republic  formation  at  the  Cascade  range  is  another 
detrital  formation  which  contains  water- worn  debris  derived  from  the 
underlying  deposits  of  jaspilite  and  ore,  and  is  therefore  uncomforina- 
bly  above  it.  At  present  it  is  not  possible  to  determine  positively 
whether  there  are  really  three  formations  as  given,  or  from  four  to  six 
different  ones,  or  whether  the  three  may  be  reduced  to  two. 
Wadsworth,115  in  1891,  finds  that  the  Lower  Silurian,  containing 
Trenton  fossils  near  L'Anse,  overlies  the  sandstone  conformably,  both 
having  a  synclinal  structure^  which  tends  to  confirm  the  commonly 
received  view  of  the  Potsdam  age  of  the  Eastern  sandstone. 
Wadsworth,116  in  1891,  gives  observations  upon  the  South  Trap 
range  and  adjacent  sandstones.    Various  places  are  mentioned,  includ- 
