50  PRE-CAMBRIAN    GEOLOGY   OF    NORTH   AMERICA. 
northern  and  southern  districts  the  acidic  rocks  are  dominant.  More- 
over, it  is  stated  that  the  basic  rocks  are  oldest  and  are  intruded  by 
the  acidic  gneisses.  Thus  we  apparently  have  in  the  Archean  com- 
plex the  equivalent  of  the  Keewatin  and  Laurentian,  as  we  use  these 
terms  in  America,  with  like  relations. 
The  Scotland  area  also  is  one  which  illustrates  the  faulting 
deformation  of  the  pre-Cambrian  upon  a  great  scale,  which  also 
affects  the  post-Cambrian  rocks.  As  a  result  of  most  remarkable 
overthrust  faults  developed  in  the  post-Cambrian,  the  eastern  rocks 
were  driven  toward  the  west,  were  folded  over  one  another,  snapped 
across,  and  piled  up  in  successive  slices,  giving  gently  dipping  east- 
ward limbs  and  steeply  inclined  western  limbs.  The  more  Avesterly 
of  these  thrusts  detach,  bring  up,  and  drive  westward  portions  of  the 
old  floor  of  Lewisian  gneiss,  together  with  the  Torridon  sandstone 
and  many  of  the  fossiliferous  zones  of  the  Cambrian.  The  slices 
of  Lewisian  o-neiss  sometimes  exceed  1,000  feet  in  thickness,  and 
they  present  the  characteristic  types  of  these  rocks  as  developed 
in  the  undisturbed  area  to  the  west.  In  certain  localities  inversions 
occur  on  a  stupendous  scale,  as,  for  example,  to  the  north  and  south 
of  Strome  Ferry,  where  a  portion  of  the  old  Archean  floor  of  gneiss 
has  been  turned  upside  down  and  reposes  on  the  inverted  basal  beds 
of  the  Torridon  sandstone,  which  dip  at  gentle  angles  to  the  east- 
southeast. 
The  most  easterly  and  perhaps  the  most  powerful  of  these  disrup- 
tions, to  which  the  name  "  Moine  thrust  "  has  been  given,  differs  from 
all  those  to  the  west  in  two  important  points.  First,  the  materials 
overlying  that  plane  comprise  the  Eastern  schists,  which  possess  dif- 
ferent petrographical  characters  from  the  displaced  masses  to  the 
west.  Secondly,  in  some  instances  the  strata  overlying  this  plane 
have  been  driven  so  far  west — for  10  miles  at  least  in  the  Durness 
area — that  they  rest  almost  directly  on  the  undisturbed  Cambrian 
rocks.  Hence  arise  those  deceptive  sections  where  there  seems  to  be 
a  normal  sequence  from  the  fossiliferous  Cambrian  zones  into  the 
Eastern  schists. 
In  England  and  Wales  the  pre-Cambrian  occupies  small  areas  and 
its  stratigraphy  is  less  well  known. 
SCANDINAVIA. 
Scandinavia  exhibits  the  largest  continuous  tract  of  pre-Cambrian 
rocks  in  Europe.  They  may  be  regarded  as  an  extension  on  the  main- 
land of  those  of  Britain  and  are  believed  by  Geikie  to  be  similar  in 
general  geological  features.     In  western  Norway  the  Archean  may 
