vanhise.]  LAKE    SUPERIOR    REGION.  89 
the  amygdaloid  as  due  to  the  fusion  of  the  lower  portions  of  the  sedi- 
mentary rocks. 
At  Presque  isle  is  a  little  isolated  knob  of  trap  which  has  been  up- 
lifted, as  is  shown  by  the  way  in  which  the  stratification  of  the  adjacent 
sedimentary  rocks  has  been  disturbed.  They  invariably  dip  at  a  high 
angle  in  all  directions  from  the  trap.  At  the  immediate  line  of  junction 
the  character  of  both  rocks  is  lost,  and  the  sedimentary  rocks  for  a 
distance  of  several  hundred  feet  have  been  shattered  while  retaining 
their  original  position,  and  were  again  cemented  by  an  injection  of  cal- 
careous matter. 
The  area  of  country  occupied  by  the  metamorphic  group  is  less  than 
by  the  Primary  or  Trap.  The  group  is  made  up  of  an  alternating  series 
of  talcose  and  mica-slates,  graduating  into  clay-slates,  with  quartz  and 
serpentine  rocks,  the  quartz  rocks  being  by  far  the  most  abundant. 
The  metamorphic  rocks  are  occasionally  traversed  by  trap  dikes. 
The  conglomerate  rock,  the  lowest  of  the  sedimentary  rocks,  is  inva- 
riably connected  with  or  rests  upon  the  trap  rock.  It  is  very  variable 
in  thickness  and  is  without  doubt  a  trap  tuff  which  has  accumulated  or 
deposited  around  the  conical  knobs  of  trap  during  their  gradual  eleva- 
tion. The  pebbles  of  the  rock  consist  of  rounded  masses  of  greenstone 
and  amygdaloid.  They  are  usually  firmly  cemented  by  calcareous  and 
argillaceous  material.  Eesting  conformably  upon  the  conglomerate  is 
a  mixed  conglomerate  and  sandrock.  This  mixed  rock  occurs  upon 
isle  Eoyale  and  was  seen  to  be  very  widespread  upon  the  south  shore. 
The  conglomeratic  part  of  the  mixed  rock  has  the  same  character  as  the 
conglomerate  rock.  Dikes  of  greenstone  are  found  in  this  mixed  rock, 
but  less  frequently  than  in  the  rock  below.  The  red  sandstone  is  the 
chief  rock  that  appears  upon  the  immediate  coast  of  the  south  shore  of 
lake  Superior.  The  primary,  metamorphic,  and  trap  rocks  are  almost 
invariably  surrounded  or  flanked  at  their  bases  by  this  sandrock.  The 
material  of  this  sandrock  differs  widely  from  the  conglomerate  rocks, 
for  these  are  made  up  of  materials  clearly  of  trappean  origin  and  very 
rarely  of  quartz-  while  the  red  sandstone  is  composed  of  materials  de- 
rived from  the  granitic  and  metamorphic  rocks,  in  which  quartz  occurs 
abundantly.  The  red  sandrock  is  less  frequently  traversed  by  dikes 
than  the  rocks  before  described,  although  they  are  sometimes  noticed 
traversing  the  whole  of  the  several  rock  formations,  including  the  red 
sandstone.  The  upper  or  gray  sandrock  conforms  to  the  limestone 
above  it,  and  rests  conformably  upon  the  uptilted  edges  of  the  red  sand 
rock  below. 
Winchell  (Alexander),98  in  1861,  gives  a  general  sketch  of  the 
geology  of  Michigan.  Among  the  stratified  rocks  are  placed  the  Azoic, 
while  the  unstratified  rocks  are  divided  into  Volcanic,  incln  din  g  lava,  trap, 
etc.,  and  Plutonic,  including  granite,  syenite,  etc.  The  Azoic  rocks  arc 
of  immense  thickness  and  are  interposed  between  the  crystalline,  plutonic, 
and  volcanic  rocks  and  the  lake  Superior  sandstone.    The  rocks  in 
