[Feb.  1893, 
102  PROF.  T.  G.  BONNET  ON  SOME  SCHISTOSE 
is  intrusive  in  the  schistes  a  cTiloritoide.  A  similar  resemblance  to 
some  of  these  Alpine  rocks  may  be  observed  in  an  amphibolite  from 
near  Le  Poldu  (Britanny)d  The  hornblende-schists  from  the 
Hebridean  series  of  Boss-shire,  where  much  affected  by  pressure, 
become  aetinolitic.2  Bo  also  are  the  ‘green  schists  from  the  south 
coast  of  the  Lizard  (where  the  rock  is  indubitably  much  affected  by 
pressure),  from  near  the  great  boundary-fault  at  Porthalla,  and  in 
one  case  at  Polkerris.3  But  the  ordinary  dark  hornblende-schists,  as 
already  described,  exhibit  quite  a  different  structure,  which  more 
nearly  resembles  that  of  the  foliated  part  of  the  dyke  in  Caerleon  Cove 4 
and  the  portion  of  the  Scourie  Dyke  figured  in  plate  xxi.  (1)  in 
Mr.  Teall’s  ‘  British  Petrography.’  In  these  (and  many  of  them 
show  a  well-marked  mineral  banding)  the  hornblende  is  more 
granular  and  normal  in  form.  So,  referring  to  the  plates  in  that 
book,  I  should  say  that  the  structure  figured  in  plates  xx.  (2)  and 
xxi.  (1)  was  due,  not  to  pressure,  but  to  a  fluxional  movement  during 
the  last  stage  of  consolidation.  That  figured  in  pi.  xx.  (1)  possibly 
may  have  been  produced  by  pressure,  but  of  this  I  am  doubtful. 
Thus  it  appears  to  me  that  an  augitic  rock  may  be  converted  into 
a  hornblendic  rock — 
(1)  By  simple  ‘  uralitization  ’  (without  foliation). 
(2)  By  the  same,  with  the  formation  of  some  aetinolitic  horn¬ 
blende,  generally  rather  minute,  often  fringing  larger  crystals 
(without  foliation). 
(3)  By  fluxional  movement  (causing  foliation)  followed  by  urali¬ 
tization. 
(4)  By  dynamo-metamorphism,5  followed  by  reconstitution,  the 
result  being  foliation. 
1  Quart.  Jcmrn.  Geol.  Soc.  vol.  xliii.  (1887)  p.  312. 
2  Since  the  above  paper  was  written  I  have  obtained  additional  evidence 
from  Scotland.  In  the  Pass  of  Killiecrankie  dioritic  dykes,  more  or  less 
schistose,  are  frequent,  some  of  which  present  interesting  resemblances  to  certain 
of  these  Alpine  ‘hornblende-schists.’  The  rocks  can  be  examined  in  situ  close 
to  the  Garry  and  occur  as  boulders  in  its  channel.  They  are  more  or  less 
foliated,  evidently  sometimes  contain  biotite,  and  not  unfrequently  red  garnet. 
Occasionally  the  former  presence  of  a  porphyritic  felspar  is  indicated  by  white 
spots,  in  other  parts  of  the  same  mass  garnets  are  abundant  (I  have  long  sus¬ 
pected  that  most  eclogites  are  diorites  in  which  garnet  has  taken  the  place  of 
felspar).  I  have  examined  microscopically  one  of  the  less  foliated  examples 
(from  a  dyke  above  the  bridge  in  the  village)  and  the  most  foliated  one  (from 
a  boulder) ;  both,  especially  the  latter,  strikingly  correspond  with  some  of  the 
rocks  described  in  this  paper,  the  hornblende  occurring  in  dark  green  prisms 
with  enclosures  (evidently  of  later  date  than  the  principal  crushing),  the  biotite 
being  newer  than  the  hornblende  and  'sometimes  suggesting  pseudomorphie 
replacement,  and  the  garnets  being  anterior  to  the  crushing. 
3  Quart.  Journ.  Geol.  Soc.  vol.  xlvii.  (1891)  pp.  480-482.  4  Ibid.  p.  493. 
5  This  seems  to  produce  the  most  complete  reconstitution  :  not  only  the  augite 
being  replaced  by  actinolite,  but  also  epidote  and  felspar  (the  latter  probably  of 
different  species  from  the  original  felspar)  appearing.  I  suspect  that  some  ol  the 
finer  granules  of  iron  oxide  sometimes  are  ‘  absorbed.’  It  is  noteworthy  that 
there  is  the  greatest  amount  of  biotite  and  the  least  of  actinolite  (indicative  of  a 
more  complete  exchange  of  constituents  between  the  augitic  and  felspatbie 
materials)  in  the  thin  dykes,  which  would  be  in  all  probability  more  crushed 
than  the  thicker  masses. 
