134  PRE-CAMBRIAN    ROCKS    OF    NORTH    AMERICA.  [bull. 5 
i 
SECTION   VI.      WORK   OF    THE    LATER   UNITED    STATES   GEOLOGISTS 
AND  ASSOCIATES. 
Hayden,190  in  1867,  in  his  sketch  of  the  geology  of  northeaster  \ 
Dakota,  describes  quartzites  along  the  James  river,  Yermilion  rivei 
and  at  Sioux  falls.     These  qnartzites  are  sometimes  conglomeratic.     O 
the  James  river  the  lines  of  stratification  are  nearly  obliterated,  but  th 
rock  appears  to  be  metamorphic.    The  pipestone  bed  on  Pipestone  cree.  I 
is  associated  with  the  quartzites  already  mentioned  and  this  rock  i 
undoubtedly  of  the  same  age.    At  Sioux  falls,  while  no  well  define* 
fossils  were  discovered,  upon  the  outer  surfaces  of  the  rocks  are  roundec 
outlines  of  what  appear  to  be  organic  remains,  but  the  peculiar  charac 
ter  of  the  quartzite  points  toward  the  Azoic  series.     The  formation  i  | 
tentatively  referred  to  the  Super- Carboniferous,  Triassic,  or  downwarc 
extension  of  the  Cretaceous ;  but  Hall's  opinion  that  this  rock  is  Hu 
ronian  is  entitled  to  great  weight. 
Irving,191  in  1883,  gives  a  systematic  account  of  the  Copper-bearing 
rocks  of  lake  Superior.  From  this  group  is  excluded  the  so-called  lowei 
group  of  Logan,  the  Animikie  group  of  Hunt,  and  also  the  horizontal 
sandstones  known  as  the  Eastern  and  Western  sandstones ;  although  il 
includes  the  dolomitic  sandstones,  with  accompanying  crystalline  rocks 
between  Black  and  Thunder  bays,  and  occupies  the  valley  of  the  Black 
Sturgeon  and  Nrpigon  rivers,  as  well  as  lake  Mpigon.  The  Keweenaw 
or  Copper-bearing  series  then  includes  the  succession  of  interbedded 
traps,  amygdaloids,  felsitic  porphyries,  porphyry-conglomerates,  and 
sandstones,  and  the  conformable  overlying  sandstone  typically  devel- 
oped in  the  region  of  Keweenaw  point  and  Portage  lake.  These  rocks 
have  their  most  widespread  extent  about  the  west  half  of  lake  Superior, 
but  also  occur  in  the  eastern  part  of  the  lake.  The  entire  geographical 
extent  in  the  immediate  basin  of  lake  Superior  is  about  41,000  square 
miles. 
The  eruptive  rocks  include  basic,  intermediate,  and  acid  kinds,  but 
there  is  no  such  chronological  relations  between  these  three  kinds  as  is 
found  to  be  the  rule  in  Tertiary  and  post-Tertiary  times.  In  the  Pali- 
sades of  the  Minnesota  coast  quartz-porphyries  are  found  both  over- 
lain and  underlain  by  basic  rocks  with  abundant  evidence  that  the 
porphyry  is  a  surface  flow.  The  same  phenomena  are  seen  at  other 
places.  Acid  flows  are  superimposed  upon  basic  flows,  flows  of  inter- 
mediate acidity  immediately  overlie  acid  flows,  flows  of  intermediate 
acidity  overlie  porphyritic  conglomerates,  flows  of  intermediate  acidity 
are  superimposed  upon  basic  flows,  basic  rocks  are  intersected  by 
acid  rocks,  basic  flows  overlie  acid  rocks,  basic  flows  overlie  those 
of  intermediate  acidity,  acid  rocks  are  intersected  by  basic  rocks. 
There  is  a  complete  absence  from  the  series  of  anything  like  volcanic 
ash.  The  detrital  rocks  of  the  series  are  composed  of  fragments  broken 
for  the  most  part  from  the  acid  rocks  of  the  series — that  is,  such  mate- 
