Yol.  49.]  4  GREENSTONES, ’  ETC.,  EROH  THE  PENNINE  ALPS.  103 
The  first  and  second  of  these  changes  (so  far  as  my  experience 
goes)  occur  in  regions  which,  offer  no  evidence  of  dynamo-meta¬ 
morphism  on  an  important  scale.  Of  course,  in  any  district  occupied 
by  ancient  roc-hs,  local  disturbances  may  have  produced  their  effects, 
so  that  a  structure  due  to  pressure  might  occur,  here  and  there, 
in  snc-h  a  neighbourhood  as  Coverack  Cove  or  the  coast  south  of 
Carrick-Luz  (Cornwall)  :  but  in  these  (to  take  them  as  an  example) 
I  believe  that  the  altered  gabbros  would  fall  under  one  of  the  first 
three  heads,  and  only  by  some  rare  chance  under  the  fourth.  IV e 
must  also  be  prepared  for  the  last  process  being  superimposed  on 
the  third,  as  already  mentioned  in  the  case  of  some  of  the  Lizard 
(hornblendic)  schists,  and  as  may  very  likely  have  happened  in 
parts  of  the  Sc-ourie  Dyke. 
Accordingly  I  believe  it  to  be  generally  possible,  in  cases  of  the 
genesis  of  a  hornblende-schist  from  an  augitic  rock  of  igneous  origin, 
to  distinguish  those  which  are  the  more  direct  product  of  dynamo- 
met  amorphism,  both  from  those  in  which  the  original  structure  is 
more  or  less  retained  (or  ordinary  epidiorites)  and  from  those  where 
the  foliated  structure  is  due  to  some  kind  of  fluxional  movement 
during  consolidation. 
I  may  remark  in  conclusion  that  the  formation  of  biotite  or 
chlorite  in  a  felspar-pyroxene  rock  probably  requires  a  greater 
amount  of  crushing  than  the  conversion  of  augite  into  actinolite. 
To  produce  the  first  two  minerals  there  must  be  an  exchange  of  con¬ 
stituents  between  the  felspars  and  pyroxenes  ; 1  biotite  comes  at  once 
from  the  partial  melting  of  hornblendite  by  an  acid  magma.2  In 
the  cases  above  described,  where  the  biotite  forms  a  kind  of  4  setting ' 
for  the  actinolite,  this  occurs  in  that  part  of  the  rock  where  the 
powder  of  the  felspars  and  pyroxenes  would  be  most  completely  mixed. 
The  thin  dykes  described  above  strongly  favour  this  conclusion,  for 
in  these  either  pulverization  would  be  most  complete,  or  the  two 
constituents  (if  the  rock  was  glassy  or  compact)  would  be  already 
mingled  in  a  state  of  fine  division,  and  it  is  in  these  that  we  find 
verv  much  chlorite  or  biotite  and  onlv  a  little  actinolite. 
*  V 
1  This,  as  I  believe  has  been  observed,  accounts  for  the  frequent  association 
of  epidote  and  saussurite. 
2  Hill  and  Bonney.  Quart.  -Journ.  G-eol.  Soc.  vol.  xlviii.  (1892)  pp.  127-lb7. 
