vanhisf,!  LAKE    SUPERIOK    REGION.  175 
That  below  the  Cherty  Limestone  of  the  Penokee  series  there  is  a 
great  physical  break  would,  in  the  face  of  the  evidence  at  present 
known,  be  hardly  doubted  by  anyone.  The  cherty  limestone,  forming 
a  single  line  of  outcrops,  although  nor  continuous,  now  rests  upon 
granite,  now  upon  gneiss,  now  upon  the  green  crystalline  schists. 
The  granite  is  definitely  known  to  be  later  than  the  schists  because  it 
intricately  intrudes  them,  but  it  never  intersects  the  cherty  limestone. 
This  basement  is  clearly  a  complex  upon  which  the  limestone  has 
been  deposited. 
Turning  now  to  the  Marquette  district:  Unconformable  contacts 
have  been  found  at  many  localities,  but  here  the  clastic  series  are 
folded,  and  certain  of  the  contacts  between  the  elastics  and  crystalline 
complex,  by  overlapping,  are  below  upper  members  of  the  clastic  series 
rather  than  truly  basal  contacts.  Of  the  two  localities  cited  by  Brooks 
for  the  unconformity  between  the  Huronian  and  Laurentian,  that  at 
Republic  mountain  is  clearly  between  the  lower  part  of  the  Marquette 
series  and  the  granite  gneiss-schist  complex,  while  that  at  Plumbago 
creek,  in  the  L'Anse  district,  is  certainly  below  a  high  horizon.  Of  the 
many  localities  cited  by  Roininger  and  Irving  in  which  there  are  con- 
tacts between  the  granite-gneiss-schist  complex  and  the  overlying  elas- 
tics, if  Brooks's  succession  be  accepted,  several  belong  well  down 
in,  if  not  actually  at,  the  base  of  the  Marquette  series.  At  these 
contacts  the  elastics  are  generally  conglomerates,  built  up  chiefly 
of  the  debris  of  the  underlying  rocks,  and  oftentimes  so  thoroughly 
cemented  as  closely  to  resemble  them  and  to  lead  to  the  conclusion,  if 
not  carefully  examined,  that  there  is  a  real  transition  between  the 
clastic  and  crystalline  rocks.  As  already  indicated,  this  was  at  first 
Rominger's  opinion,  and  the  apparent  transition  was  taken  to  indicate 
a  gradual  metamorphism  from  the  conglomerates  to  the  granite  or 
schists  as  the  case  might  be.  But  Rominger's  later  studies  led  him  to 
see,  as  did  also  Irving,  that  these  basal  conglomerates  are  recomposed 
rocks  resting  upon  an  earlier  formed  crystalline  and  often  granitic  base. 
In  the  Menominee  district  Brooks,  Rominger,  and  Irving  all  hold  that 
contacts  are  found  between  very  low,  or  the  lowest  members  of  the 
clastic  series  and  the  granite- gneiss  complex,  the  relations  being  those 
of  profound  unconformity.  The  actual  contact  described  by  Smyth 
(too  late  to  summarize  in  the  literature)  between  the  lowest  formation 
of  the  lower  Marquette  and  the  granite-gneiss  at  Republic  mountain 
is  the  clearest  case  on  the  south  shore.  Here  is  a  basal  conglomerate 
containing  numerous  water-worn  bowlders  and  pebbles  of  granite,  rest- 
ing directly  upon  the  granite  from  which  the  fragments  are  derived. 
As  shown  by  Irving,  the  magnitude  of  the  break  in  the  Penokee, 
Marquette,  and  Menominee  districts  is  not  lessened  whether  the  under- 
lying schist,  gneiss,  and  granite  are  igneous  or  sedimentary,  for  they 
had  reached  their  present  crystalline  condition  before  the  overlying 
rocks    were  deposited  upon   them,  a   condition  which    a  part   or  all 
