Yol.  49.] 
SOME  COAST-SECTIONS  AT  THE  LIZARD. 
205 
have  been  traced  50  yards  farther  south-east  (see  Map,  p.  203). 
The  fact  that  these  cut  the  banded  series  is  clearly  established  by 
tracing  the  junctions.  The  hade  of  the  dykes  is  nearly  at  right- 
angles  to  that  of  the  foliation-planes.  It  will  be  seen  by  the  map 
that  there  are  other  dykes  besides  those  which  have  been  especially 
referred  to.  Potstone,  similar  to  that  described  in  a  former  paper 
by  one  of  us,  has  been  observed  at  many  points  east  and  south-east 
of  the  locality  where  it  was  first  recognized.  It  is  well  seen  at  g, 
where  it  is  associated  with  schist  and  serpentine  in  such  a  way  as 
to  suggest  that  it  forms  a  part  of  the  banded  complex. 
In  describing  the  dykes,  we  have  frequently  referred  to  their 
passage  into  hornblende-schist.  In  the  porphyritic  varieties  the 
foliation-planes  wind  round  the  large  felspars  which  have  often 
been  squeezed  out  into  lenticular  folia.  Fluxion-structures  are, 
moreover,  strongly  marked  under  the  microscope.  Are  these  struc¬ 
tures  original  or  secondary  ?  In  previous  communications  one  of 
us  has  maintained  the  latter  view,  and  more  extended  observations 
have  not  yet  led  him  to  change  his  opinion.  A  description  of  a 
specimen  from  a  foliated  portion  of  one  of  the  dykes  near  Potstone 
Point  may  here  be  given  in  support  of  this  view. 
It  is  a  rock  possessing  linear  foliation.  White  porphyritic  fel¬ 
spars  still  showing  traces  of  idiomorphism,  but  usually  more  or  less 
rounded  and  lenticular,  lie  in  a  compact,  dark  greenish  matrix. 
Under  the  microscope  the  large  felspars  can  be  seen  to  have  suffered 
distortion  and  fracture  by  the  movement  which  produced  the 
fluxion-structure.  Seeing,  however,  that  these  felspars  were  almost 
certainly  present  in  the  magma  when  the  dyke  was  intruded,  their 
distortion  does  not  prove  that  the  rock  was  deformed  after  final 
solidification.  We  turn  then  to  the  groundmass.  This  presents  a 
somewhat  confused  appearance.  Lath-shaped  felspars  are  still 
recognizable,  but  it  is  clear  that  they  have  been  bent,  broken,  and 
converted  into  a  microcrystalline  aggregate  in  which  the  original 
form  is  partially  or  wholly  lost.  In  other  words,  cataclastic  struc¬ 
tures  are  as  clearly  discernible  in  the  felspars  of  the  groundmass  as 
they  are  in  those  which  occur  as  porphyritic  constituents.  It  is 
evident,  therefore,  that  the  deformation  which  produced  the  fluxion- 
structure  took  place  after  the  lath-shaped  felspars  had  been  pro¬ 
duced.  We  have  thus  pushed  the  operation  one  stage  nearer  that 
of  final  consolidation. 
ISfow,  the  two  generations  of  felspar  and  their  broken  fragments 
lie  in  a  fine-grained,  crystalline  aggregate,  of  which  a  pale-green, 
more  or  less  fibrous  hornblende  is  the  principal  constituent.  It  is 
in  this  aggregate  that  the  differential  movement  has  mainly  taken 
place.  Fluxion-structure  is  common  in  basaltic  lavas  and  occurs 
even  in  dykes,  but  in  no  case  known  has  the  unconsolidated  inter¬ 
stitial  matter,  which  allowed  the  structure  to  be  produced,  solidified 
as  an  aggregate  of  fibrous  hornblende;  whereas  such  hornblende 
unquestionably  arises  in  consequence  of  the  alteration  of  augite. 
To  make  the  case  still  stronger  we  want  evidence  that  the  original 
rock  was  a  dolerite,  and  that  it  did  not  possess  a  parallel  structure. 
