GENEKAL   ACCOUNT    OF    THE    PRE-CAMBRIAN    ROCKS.  51 
be  represented  by  coarse  banded  gneiss,  sometimes  with  limestone 
bands,  occupying  large  areas.  This  corresponds  to  the  Lewisian 
gneiss  of  England.  With  it  is  intimately  associated  another  group 
of  rocks,  consisting  of  quartzite,  limestone,  mica  schist,  and  quartz 
schist,  predominantly  of  sedimentary  origin.  This  is  certainly  older 
than  some  of  the  gneisses,  which  can  be  seen  to  pierce  it.  It  is  sim- 
ilar to  the  Dalradian  series  of  Scotland.  Resting  upon  the  gneisses 
unconformably  is  a  later  group  of  mica  schists,  phyllites,  quartz 
schists,  clay  slates,  quartzites,  and  schistose  conglomerates,  associated 
with  schists  probably  of  eruptive  origin.  The  age  of  this  group  is 
not  clear;  part  of  it  is  as  late  as  Silurian,  part  of  it  may  well  be  Al- 
gonkian.  The  similarity  of  a  part  of  these  rocks  to  the  Torridonian 
series  is  close. 
In  Sweden  a  similar  subdivision  of  the  pre-Cambrian  rocks  is  pos- 
sible. The  terms  Algonkian  and  Proterozoic  have  been  applied  by 
Tornebohm  to  cover  the  pre-Cambrian  sedimentary  rocks.  He  divides 
these  rocks  into  Upper  and  Lower  Algonkian.  His  upper  series  is 
doubtless  Algonkian  as  Ave  use  the  term,  but  it  is  not  certain  that  the 
lower  series  is  not  Archean,  at  least  in  part.  There  is  marked  differ- 
ence between  the  pre-Cambrian  on  the  eastern  and  western  sides  of 
the  Scandinavian  peninsula,  and  the  western  side  also  has  been  sub- 
jected to  much  more  metamorphism  than  the  eastern  side.  The  con- 
tent of  iron  ores  is  a  feature  which  emphasizes  their  similarity  to  the 
Lake  Superior  pre-Cambrian. 
FINLAND. 
Most  of  Finland  is  covered  by  pre-Cambrian  rocks  with  characters 
similar  to  those  of  Sweden. 
Sederholm,a  in  1007,  discusses  the  pre-Cambrian  geology  of  eastern 
"  Fenno-Scandia,"  especially  the  origin  of  the  granites  and  gneisses, 
and  presents  a  geological  map  of  "  Fenno-Scandia."  The  succession 
is  as  follows: 
Succession  of  pre-Cambrian  rocks  in  "  Fenno-Scandia." 
Names  of  the  subdivisions. 
Supercrustal  rocks. 
Infracrustal  rocks. 
Jotnian. 
Diabases,    sandstones,    labrador- 
ites,  conglomerates. 
Rapakivi  granites. 
Unconformity. 
a  Sederholm,  J.  J*.,  Om  Granil  och  Gneiss,  deras  uppkomst,  upptradande  och  utbred- 
ning  inom  urberget  i  Fennoskandia :  Bull.  Comm.  Geol.  de  Finlande,  No.  23,  1907.  (With 
English  summary  of  contents. 
