Vol.  49.] 
£  GREENSTONES,’  ETC.,  FROM  THE  PENNINE  ALPS. 
101 
A  fourth  specimen,  from  the  Gorge  of  Gondo,1  when  examined 
macroscopically  and  microscopically,  only  exhibits  varietal  differ¬ 
ences  from  those  above  described. 
Examples  of  like  kind  from  other  parts  of  the  Alps  might  be 
added,  but  these  may  suffice.  They  suggest  the  following  con¬ 
clusions  : — 
(1)  That  basic  intrusive  rocks,  presumably  once  dolerites  or 
basalts,  can  be  converted  into  foliated,  possibly  even  slightly  banded 
schists,  in  which  no  recognizable  trace  of  the  original  structure 
remains. 
(2)  That  in  an  early  (possibly  the  first)  stage  of  the  process  the 
primary  constituents  of  the  rock-mass  are  crushed  or  sheared,  and 
thus  their  fragments  frequently  assume  a  somewhat  ‘  streaky  ’  order  ; 
that  is  to  say,  the  rock  passes  more  or  less  into  the  mylonitic 
condition. 
(3)  That  next  (probably  owing  to  the  action  of  water  under 
great  pressure)  certain  of  the  constituents  are  decomposed  or 
dissolved. 
(4)  That  in  consequence  of  this,  when  the  pressure  is  sufficiently 
diminished,  a  new  group  of  minerals  is  formed  (though  in  some 
cases  original  fragments  may  serve  as  nuclei). 
(5)  That,  of  these,  hornblende  is  the  earliest  formed,2  closely 
followed,  if  not  accompanied,  by  epidote  :  next  comes  biotite  (the 
growth  of  which  often  suggests  that  by  this  time  the  pressure  was 
ceasing  to  be  definite  in  direction 3),  and  lastly  the  water-clear 
felspar  and  quartz. 
In  all  these  cases  the  hornblende  occurs  either  in  very  elongated 
prisms  or  in  actual  needles  (in  other  words,  is  more  or  less  actino- 
litic).  The  inference  that  this  form  of  the  mineral  and  pressure 
frequently  stand  in  the  relation  of  effect  and  cause  is  supported  by 
not  a  few  instances  in  my  collection.  Thus  the  glaucophane  in  the 
amphibolite  of  the  He  de  Groix  4  commonly  occurs  in  rather  long- 
bladed  prisms,  and  the  general  aspect  of  the  rock  recalls  some  of 
the  above  described,  less  fissile  ‘  hornblende-schists  ’  from  the  Alps. 
The  whole  region  has  obviously  been  subjected  to  great  pressure, 
and  I  think  it  highly  probable  that  the  amphibolite  a  glaucophane 
1  Seen  at  the  roadside  a  little  above  the  Alte  Kaserne.  It  has  apparently 
been  injected  between  the  beds  of  the  cale-mica-schists  and  subsequently  sub¬ 
jected  to  great  pressure  together  with  the  surrounding  rocks.  It  is  nowhere 
more  than  7  feet  in  thickness,  and  in  the  cliff-face  west  of  the  chalets  of  Alpigen 
it  is  seen  to  break  across  the  bedding  of  the  surrounding  schists  and  finally  to 
die  out. — J.  Eccles. 
-  The  rutile,  zircon,  and  some  of  the  iron  oxides  are  probably  original  con¬ 
stituents — the  sphene  may  in  some  cases  be  secondary.  Calcite  of  course,  when 
present,  would  form  at  a  late  stage. 
3  For  the  present  the  question,  whether  the  ‘  chlorite  ’  is  an  alteration- 
product  of  biotite  or  independently  produced,  may  be  left  open.  In  some  cases 
i  think  it  the  former.  Boubtless,  much  would  depend  upon  the  amount  of 
alkali  originally  present  in  the  rock  or  introduced  by  water. 
4  Quart.  Journ.  Gfeol.  Soc.  vol.  xliii.  (1887)  pp.  302-804.  See  also  the  figure 
of  the  Anglesey  glaucophane-schist,  Teall,  ‘  Brit.  Petrogr.’  pi.  xlvii  (1).  In  my 
specimen  of  glaucophane-sshist  from  Japan  the  mineral  is  in  very  long  prisms. 
