52  PRE-CAMBRIAN   ROCKS   OF   NORTH    AMERICA.  [bull.  86. 
one  place  alone  transition  limestone,  with  perhaps  traces  of  gray  wacke. 
Third,  trap  or  overlying  rock,  the  most  of  which  is  amygdaloid ;  various 
kinds  of  porphyry  are  next  in  quantity ;  then  trap,  greenstone,  syenites, 
and  pitchstone.  Fourth,  the  medial  order,  the  only  rock  of  which  is 
the  Old  Eed  sandstone.  Then  follows  an  account  of  the  distribution 
of  each  of  these  orders.  The  amygdaloid  with  little  doubt  rests  upon 
the  syenite  and  granite,  although  the  junction  was  never  seen.  The 
amygdaloid  passes  into  greenstone  on  the  one  hand  simply  by  being 
divested  of  its  nodules,  and  into  porphyry  on  the  other.  The  Old  Bed 
sandstone  may  be  traced  from  one  extremity  of  the  lake  to  the  other. 
Its  existence  is  noticed  on  both  shores,  and  it  is  traced  across  the  lake 
by  many  of  the  islands,  so  as  to  leave  no  doubt  of  its  being  a  general 
formation  throughout  the  whole  of  the  basin  of  lake  Superior.  It  is 
generally  horizontally  stratified  or  nearly  so.  There  are  many  instances 
of  the  conjunction  of  the  sandstone  and  granite,  winch  serve  to  prove 
that  the  sandstone  was  deposited  after  the  granite  occupied  its  present 
position.  The  sandstone,  when  conglomeratic,  as  is  very  frequently 
the  case,  contains  fragments  of  the  trap  as  well  as  of  the  inferior  order, 
which  are  rounded  by  attrition,  and  it  is  therefore  plain  that  the  sand- 
stone is  later  than  the  trap  rocks.  Organic  remains  were  sought  in 
this  rock,  but  never  discovered.  It  is  placed  as  the  Old  Eed  because 
of  its  position  immediately  on  the  granite,  its  structure,  and  component 
parts. 
Bayfield,3  in  1845,  places  with  the  Primary  rocks  most  of  the  elas- 
tics on  the  north  shore  of  lake  Superior.  These  are  cut  by  various 
greenstones.  A  red  sandstone  forms  nearly  the  entire  southern  bound- 
ary of  the  lake.  In  places  it  is  shattered  by  the  upheaval  of  granite 
and  by  trap  rocks  which  enter  into  the  composition  of  its  conglomer- 
ates. At  Mpigon  bay  it  is  overlaid  by  an  immense  bed  of  greenstone. 
It  is  probable,  although  not  certain,  that  this  sandstone  underlies  the 
fossiliferous  red  sandstone  of  St.  Marys. 
Logan,4  in  1847,  in  a  report  on  the  geology  and  economic  minerals  of 
lake  Superior,  gives  an  account  of  a  rather  detailed  examination  of  the 
north  shore  of  lake  Superior  from  Pigeon  river  to  Sault  Ste.  Marie. 
Michipicoten  island  was  also  examined.  Lake  Superior  appears  to  be 
set  in  a  geological  depression,  which  presents  formations  of  a  similar 
character  on  both  the  north  and  south  sides,  dipping  to  the  center. 
The  series  on  the  north,  in  ascending  order,  consists  of  the  following: 
(1)  Granite  and  syenite ;  (2)  gneiss;  (3)  chloritic  and  partially  talcose 
and  conglomerate  slates;  (4)  bluish  slates  or  shales,  inter  stratified  with 
trap;  (5)  sandstones,  limestones,  indurated  marls,  and  conglomerates, 
interstratified  with  trap.  The  gneiss  is  succeeded  by  dark  green  slates, 
which  at  the  base  appear  to  be  occasionally  interstratified  with  beds  of 
the  subjacent  granite  and  gneiss.  These  slaty  beds  at  times  have  the 
quality  of  a  greenstone,  at  times  a  mica-slate,  and  a  few  are  quartz 
rocks.    Higher  in  the  series  are  conglomerates,  the  pebbles  of  which 
