48 
PRE-CAMBKIAN    GEOLOGY   OF    NOKTH   AMERICA. 
The  results  of  their  long  labors  appear  in  an  excellent  memoir  pub- 
lished in  1907.a 
Their  succession  is  as  follows:6 
iv.  Eastern  schists- 
in.  Cambrian. 
Flaggy  quartz  schists,  quartz-biotite  granulites  and  gar- 
netiferous  muscovite-biotite  schists,  with  occasional  in- 
liers  of  deformed  or  reconstructed  Lewisian  gneiss. 
Zone  of  mylonized  rocks  usually  at  the  base  of  this  series. 
Great  disruption   line — the  Moine  thrust — which  has   driven   the  Eastern 
schists  (iv)  over  the  rocks  below  (in,  n,  i). 
3.  Dolomites  and  limestones,  with  certain  fossil  if erous 
zones. 
2.  Serpulite  grit  and  fucoid  beds  yielding  the  Olenellus 
fauna. 
1.  Quartzites  with  worm  casts  in  the  upper  portions  and 
false-bedded  grits  below. 
Unconformability — plane  of  marine  denudation. 
3.  Sandstones  and  dark  micaceous  shales. 
2.  Thick  series  of  coarse  sandstones  and  grits  with  con- 
glomerate bands. 
1.  Dark  and  gray  shales  with  calcareous  bands,  fine- 
grained sandstones,  and  grits  with  epidotic  grits  at 
the  base. 
Strong  unconformability — highly  eroded  land  surface. 
2.  A  great  series  of  igneous  rocks  intrusive  in  that  com- 
plex, in  the  form  of  dikes  and  sills. 
1.  A  fundamental  complex,  composed — 
n.  Torridonian. 
i.  Lewisian. 
(a)  Mainly  of  gneisses  that  have  affinities,  both 
chemically  and  mineralogically,  with  plutonic 
igneous  products,  and 
(&)  Partly  of  crystalline  schists,  which  may  be  re- 
garded as  probably  of  sedimentary  origin. 
As  to  the  importance  of  the  unconformity  between  the  Torridonian 
and  the  Lewisian,  Home  says : c 
One  of  the  most  impressive  features  in  the  history  of  the  Lewisian  gneiss  is 
the  abundant  evidence  of  prolonged  denudation  between  the  cessation  of  the 
terrestrial  movements  just  described  and  the  deposition  of  the  Torridon  sand- 
stone. During  the  protracted  interval  represented  by  this  denudation  the  gneiss 
plateau  formed  a  land  surface  which  was  carved  into  lofty  hills  with  craggy 
slopes  and  deep  valleys.  This  fragment  of  primeval  Europe  has  been  preserved 
under  the  pile  of  coarse  Torridonian  grits  and  sandstones'  which  is  now  under- 
going slow  removal  by  the  agents  of  waste.  The  observer  may  climb  one  of 
these  Archean  hills,  following  the  boundary  line  between  the  Lewisian  rocks  and 
the  younger  formation,  and  note,  step  by  step,  how  the  subangular  fragments  of 
hornblende  schist  that  fell  from  the  pre-Torridonian  crags  are  intercalated  in 
the  grits  and  sandstones,  thus  indicating  the  slow  submergence  of  the  old  land 
a  The  geological  structure  of  the  Northwest  Highlands  of  Scotland,  by  B.  N.  Peach, 
John  Home,  the  late  W.  Gunn,  C.  T.  Clough,  and  L.  W.  Hinxman,  with  penological 
chapters  and  notes  by  J.  J.  H.  Teall.  Edited  by  Sir  Archibald  Geikie.  Mem.  Geol.  Sur- 
vey of  Great  Britain,  1907. 
6  Op.  cit.,  pp.  9-10,  33. 
c  Op.  cit,  p.  4. 
