112  PRE-CAMBRIAN    GEOLOGY    OF    NORTH    AMERICA. 
tents  of  the  sandstone  are  identical  with  those  of  Nova  Scotia,  Con- 
necticut, Massachusetts,  and  New  Jersey,  belonging  to  the  New  Red 
sandstone  series;  and  that  the  Lake  Superior  sandstone  belongs  to 
this  age  has  been  confirmed  by  the  discovery  by  C.  F.  Merion  of  a 
tract  of  limestone  in  the  midst  of  the  sandstone  of  Keweenaw  Point 
near  L'Anse.  The  limestone  contains  Pentamerus  oblongus,  and,  ac- 
cording to  Whitney,  has  a  dip  of  30°,  while  the  overlying  sandstone 
is  horizontal  and  has  been  deposited  around  it.  The  sedimentary 
strata  have  undergone  great  change  by  the  action  of  the  trap  rocks. 
Along  the  line  of  the  junction  a  chemical  combination  of  the  materials 
of  the  sandstones  and  trap  rocks  took  place,  forming  the  vesicular 
trap  called  amygdaloid,  while  there  has  further  resulted  from  this 
action  a  brecciated  Or  trap  tuff,  consisting  of  broken  pieces  of  amygda- 
loid and  sandstone.  At  other  times  the  sandstone  is  indurated  into 
a  flinty  red  rock  resembling  jasper.  At  the  Copper  Falls  mine  is 
a  case  of  what  appears  to  be  an  Orthocera  in  the  breccia  of  amygda- 
loids  and  altered  limestones.  May  it  not  have  been  torn  from  a 
subjacent  bed  of  Silurian  limestone  by  the  agency  of  the  intruded 
trap  rocks?  At  the  coast  off  Lac  la  Belle  the  sandstone  in  contact 
with  trap  has  a  dip  to  the  south  of  30°,  while  at  Point  Isabelle  the 
sandstone  cliffs  are  nearly  horizontal. 
Locke,13  in  1850,  finds,  near  L'Anse,  that  the  trappean  rocks  contain 
fragments  of  slate  distributed  through  it  and  converted  into  a  horn- 
stone  when  in  small  pieces,  like  the  eruptive  granite  of  Pigwacket 
Mountain,  New  Hampshire.  At  point  No.  2,  west  of  Presque  Isle, 
is  a  junction  of  red  sandstone  and  syenite.  The  mass  of  syenite  in- 
tersected by  dikes  of  trap  is  under  the  sandstone  and  seems  to  have 
but  slightly  affected  it. 
Foster  and  Whitney,14  in  1850,  accompany  their  synopsis  of  their 
explorations  by  geological  maps  of  the  region  between  Portage  Lake 
and  Montreal  River,  Keweenaw  Point,  Isle  Royal,  and  the  region  be- 
tween Keweenaw  Bay  and  Chocolate  River. 
Whitney,15  in  1850,  finds  the  rocks  in  the  district  between  Portage 
Lake  and  the  Ontonagon  River  to  comprise  the  following:  First,  the 
red  sandstone  of  Lake  Superior,  the  age  of  which  can  not  be  deter- 
mined, as  it  is  destitute  of  fossils.  It  lies  directly  upon  the  granite 
rocks.  Second,  a  bed  of  fossiliferous  limestone  of  the  Lower  Silurian 
system,  which  occurs  in  an  isolated  position  and  has  but  a  limited  ex- 
tent, and  the  relations  of  which  to  the  sandstone  have  not  been  deter- 
mined with  certainty.  Third,  the  trappean  rocks.  Fourth,  granitic 
and  syenitic  rocks,  with  hornblende  and  greenstone.  The  farther  the 
red  sandstone  is  removed  from  the  trappean  rocks,  so  much  nearer 
do  its  strata  approach  to  the  horizontal  and  also  become  lighter  in 
color  and  more  fragile.  The  conglomerate  of  Keweenaw  Point  oc- 
curs mixed  and  intercalated  in  such  a  manner  with  the  sandstone  as 
