Yol.  49.]  SOME  COAST-SECTIONS  AT  THE  LIZARD.  201 
teristic  network  of  magnetite,  and  a  few  grains  of  picotite.  The 
hornblende-schist  is  composed  of  pale-brown  hornblende,  colourless 
malacolite,  and  more  or  less  altered  felspar.  Another  specimen  from 
the  same  locality  illustrates  the  interbanding  of  the  two  types  of  rock 
in  a  still  more  perfect,  manner.  Numerous  laminae,  no  thicker  than 
sheets  of  cardboard,  alternate  with  each  other.  The  bands  of  schist 
are  composed  of  hornblende,  malacolite,  and  turbid  felspar.  In  some 
bands  the  hornblende  is  pale  green  in  colour,  in  others  brown. 
Detached  olivines  with  strings  of  magnetite  may  be  observed  along 
certain  planes,  and  by  the  increase  in  the  number  of  these  olivines 
and  in  the  thickness  of  the  zone  in  which  they  are  developed  bands 
of  peridotite  have  been  formed,  and  from  these  serpentine  has  been 
produced  in  the  usual  way.  As  the  olivine  increases  the  felspar 
diminishes,  but  the  hornblende  of  the  serpentine  is  absolutely  iden¬ 
tical  in  structure  and  mode  of  development  with  that  of  the  schist. 
The  hornblende  of  the  schist  associated  with  the  serpentine  is 
usually  brown,  and  not  green,  as  in  the  common  type  of  hornblende- 
schist  ;  but  we  have  found  brown  hornblende  in  the  schists  of  this 
locality,  even  when  they  are  developed  on  a  large  scale,  and  have  the 
macroscopic  characters  of  the  typical  hornblende-schist  of  the  Lizard. 
The  white  augite  (malacolite),  first  recognized  by  Lieut.-Gen. 
McMahon,  is  a  feature  of  these  rocks,  and  one  band  of  the  zone 
marked  a  (see  Map,  p.  203)  contains  it  to  the  exclusion  of  hornblende. 
A  hand-specimen  of  this  band  is  massive,  grey,  and  fine-grained. 
Under  the  microscope  it  is  seen  to  be  a  granular  aggregate  of  mala¬ 
colite,  altered  felspar,  and  iron  ores,  with  biotite  occurring  as  an 
unimportant  accessory.  This  rock  is  connected  with  the  normal 
schists  by  intermediate  varieties,  and  must,  therefore,  be  regarded 
as  forming  a  band  of  exceptional  composition.  The  serpentines 
interbanded  with  the  schists  belong  to  the  olivine-hornblende  variety. 
They  are  themselves  frequently  well  banded,  in  consequence  of 
variations  in  the  relative  proportions  of  the  two  principal  con¬ 
stituents  ;  and  this  banding,  so  far  as  we  have  been  able  to  determine, 
is  parallel  with  that  of  the  schist,  when  allowance  is  made  for  the 
effects  of  disturbance. 
So  far  we  have  been  referring  only  to  banding ;  but  occasion¬ 
ally  lenticles  of  serpentine  may  be  observed  in  the  schist,  and  when 
this  is  the  case  the  foliation-planes  in  the  schist  wind  round  the 
lenticles. 
It  is  no  part  of  our  present  purpose  to  enter  into  a  discussion  of  the 
causes  which  have  produced  the  banded  complex.  They  were  pro¬ 
bably  similar  to  those  which  have  given  rise  to  banded  gneisses  of 
igneous  character  all  the  world  over.  The  occurrence  of  banded 
peridotites  as  an  integral  part  of  gneissose  formations  is  known  in 
the  north-west  of  Scotland  and  in  Norway.1  The  last-mentioned 
occurrence  is  particularly  interesting,  because  the  peridotite  would 
give  by  alteration  a  serpentine  closely  resembling,  if  not  identical 
with,  that  of  the  district  under  consideration. 
1  W.  C.  Brogger,  ‘  Ueber  Olivin-fels  von  Sondmore,’  Neues  Jahrb.  1880, 
vol.  ii.  p.  187. 
