vanhise.1  LAKE    SUPERIOR    REGION.  75 
with  which  it  alternates.  At  the  line  of  junction  of  the  trap  rocks  and 
sandstone  the  two  are  interfused,  producing  the  metamorphic  rock 
amygdaloid,  which  resembles  the  vesicular  lavas  of  volcanoes,  but  has 
its  cavities  filled  with  a  great  variety  of  curious  and  interesting  min- 
erals. On  isle  Roy  ale  about  one  quarter  of  the  area  is  sandstone  and 
conglomerate  and  the  remainder  trap,  which  formed  ridges  extending 
the  whole  length  of  the  island. 
Whitney,61  in  1849,  describes  the  iron  ore  of  the  upper  peninsula  of 
Michigan  as  existing  in  the  form  of  solid  ridges  and  knobs  inter  stratified 
with  banded  jasper,  the  whole  evidently  of  igneous  origin. 
Agassiz,6'2  in  1850,  describes  the  outlines  of  the  shore  of  lake  Supe- 
rior as  largely  due  to  six  different  sets  of  dikes  of  different  mineral- 
ogical  character,  and  each  system  running  parallel  to  one  of  the  main 
shores  lines,  although  it  would  be  a  mistake  to  ascribe  the  form  to  any 
single  geological  event.  Its  position  in<  the  main  is  doubtless  deter- 
mined by  a  dislocation  between  the  primitive  range  north  and  the  sedi- 
mentary deposit  south.  The  rocks  of  the  north  shore  of  lake  Superior 
are  extensively  metamorphic.  The  new  red  sandstone  passes  into  por- 
phyries, into  quartzite,  granite  and  gneiss,  the  metamorphism  being 
more  or  less  perfect,  so  that  the  stratification  is  still  sometimes  pre- 
served or  passes  gradually  into  absolutely  massive  rocks. 
Jackson,63  Dickenson,  McIntyre,  Barnes,  Locke,  Foster  and 
Whitney,  Gtbbs,  Hill,  Burt,  and  Hubbard,  in  1850,  report  upon 
the  mineral  lands  south  of  lake  Superior  in  the  state  of  Michigan. 
Jackson,64  describes  the  red  sandstones  and  conglomerates  of  Ke- 
weenaw point  as  existing  there  anterior  to  the  elevation  of  the  trap 
rocks,  being  derived  from  the  deposition  of  fine  sand  and  pebbles  from 
preexisting  Primary  rocks,  such  as  granite,  gneiss,  or  mica- slate.  Por- 
phyry furnishes  a  large  portion  of  the  debris,  but  it  is  doubtful  if  this  is 
not  a  semi- fused  sandstone.  There  is  no  reason  to  believe  that  igneous 
agencies  had  anything  to  do  with  the  origin  of  the  pebbles  of  the  con- 
glomerate, for  they  are  rounded  by  the  action  of  water.  From  the 
circumstance  that  the  conglomerate  borders  the  trappean  rocks  it  is 
supposed  an  ancient  shore  may  have  existed  along  that  line.  It  is  cer- 
tain that  the  finer  sandstone  is  more  remote  from  the  trap  than  the  con- 
glomerate is,  and  that  it  is  less  uplifted  and  inclined  as  it  recedes  from 
the  trap  band.  Near  the  junction  of  the  two  rocks  the  strata  dip  25° 
or  30°,  while  remote  from  it  the  sandstone  is  nearly  horizontal.  The 
mineral  composition,  association,  and  contents  of  the  sandstone  are  iden- 
tical with  those  of  Nova  Scotia,  Connecticut,  Massachusetts,  and  New 
Jersey,  belonging  to  the  new  red  sandstone  series;  and  that  the  lake 
Superior  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  the  Anse.  The  limestone  contains  Pentameruq 
oblongm,  and  according  to  Whitney  has  a  dip  of  30°,  while  the  overly- 
ing sandstone  is  horizontal  and  has  been  deposited  around  it.    The 
